Category Archives: Software Defined Radio

A review of the Icom IC-705 QRP Portable SDR Transceiver

The following review was first published in the February 2021 issue of The Spectrum Monitor magazine:


It sometimes seems that one of the biggest enemies of a radio enthusiast these days is RFI (radio frequency interference), which is to say, human-originated noise that infiltrates––and plagues––vast chunks of our radio spectrum.

Yet I believe RFI has, in a sense, also managed to energize––and even mobilize––many radio enthusiasts. How? By drawing them out of their houses and shacks into the field––to a local park, lake, river, mountain, woodland, or beach––away from switching power supplies, light dimmers, street lights, and other RFI-spewing devices.

Shortwave and mediumwave broadcast listeners have it easy, comparatively speaking. They can simply grab a favorite portable receiver, perhaps an external antenna, then hit the field to enjoy the benefits of a low-noise environment. In that a portable receiver is something of a self-contained listening post, it’s incredibly easy to transport it anywhere you like.

Ham radio operators, on the other hand, need to pack more for field operations. At a minimum, they need a transceiver, an antenna, a power source, not to mention, a mic, key, and/or computing device for digital modes. Thankfully, technology has begun miniaturizing ham radio transceivers, making them more efficient in the use of battery power, and integrating a number of accessories within one unit.

Photo from the 2019 Tokyo Ham Fair

Case in point: in 2019 at Tokyo’s Ham Fair, Icom announced their first QRP (low-power) radio in the better part of two decades: the Icom IC-705.

Introducing the Icom IC-705

 

It was love at first sight among fans of Icom when the 2019 announcement was made. Why? The instant thrill came courtesy of the IC-705’s resemblance––in miniature––to the IC-7300, one of Icom’s most popular transceivers of all time. Not only that, but the IC-705 sported even more features and a broader frequency range than the IC-7300. What wasn’t to love?

But of course, unlike the IC-7300, which can output 100 watts, the IC-705’s maximum output is just 10 watts with an external 12V power source, or 5 watts with the supplied Icom BP-272 Li-ion battery pack. Nevertheless, enthusiasts who love field radio––this article’s writer being among them––were very pleased to see Icom design a flagship QRP radio that could take some portable operators to the next level. Power was traded for portability, and for field operators, this was a reasonable trade.

And since, again, the IC-705 has even more features, modes, and frequency range than the venerable IC-7300, I felt it important to note them up front. Here are a few of its most notable features, many of which are not available on its bulkier predecessor:

  • VHF and UHF multimode operation
  • D-Star mode
  • Built-in GPS
  • Built-in Wifi connectivity
  • Built-in Bluetooth connectivity
  • Portable size
  • Battery power

The receiver design is similar to the IC-7300 below 25 MHz in that it provides a direct conversion. Above 25 MHz, however, it operates as a superheterodyne receiver. While the user would never know this in operation, it’s a clever way for Icom to keep costs down on such a wideband radio.

At time of publishing, there are no other portable transceivers that sport all of the features of the Icom IC-705. It has, in a sense, carved out its very own market niche…At least for now.

I’ve owned the IC-705 since late September 2020, and I still haven’t fully explored this radio’s remarkable capabilities. It’s really a marvel of ham radio technology, and I’m having fun exploring what it can do.

One conspicuous omission

Let’s go ahead and address this promptly. The IC-705 does have one glaring shortcoming.  It lacks one feature that is standard on the larger 100-watt IC-7300: an internal antenna tuner (ATU).

To be frank, I was a little surprised that the IC-705 didn’t include an internal ATU, since it otherwise sports so many, many features. Not having an internal ATU, like a number of other general coverage QRP transceivers in its class, definitely feels like a missed opportunity. With an ATU, the ‘705 would truly be in a class of its own.

I’m sure Icom either left the internal ATU out of the plan due to space limitations––perhaps wanting to keep the unit as compact as possible?––or possibly to keep the price down? I’m not sure.  At release, the price was $1300 US, which is undoubtedly on the higher side of this market segment; at that price point, it might as well have included an ATU.

With that said, not having an internal ATU is still not a disqualifier for me. Why? Because I have a number of resonant antennas I can add on when in the field, a remote ATU at home, and a couple of portable external ATUs, as well. Yes, it would be helpful to have it built in––as on my Elecraft KX1, KX2, and KX3, or on the ($425) Xiegu G90––but for me it’s not a deal-breaker.

One other minor omission? A simple tilt stand or foot. I do wish Icom had included some sort of foot on the bottom of the IC-705 so that it could be propped up for a better angle of operation. Without a tilt stand or foot, the IC-705 rests flat on a surface, making its screen a bit awkward to view. Of course, a number of third-party tilt stands are available on the market. And if you have a 3D printer or access to one, you can find a wide variety of options to simply print at home. I printed this super simple tilt foot, which works brilliantly.

But why not include one, Icom?

My 3D printed tilt foot

But while the IC-705 lacks a tilt foot, it actually sports a number of connection points on the bottom, including a standard tripod mount. Thank you, Icom, for at least including that (other radio manufactures please take note)!

Initial impressions

Funny: the IC-705 is the first new transceiver I’ve purchased with a color box.

If you’ve ever owned or operated the Icom IC-7300, you already know how to operate many of the functions on the IC-705. The user interfaces on the touch screens are identical. Features that are unique to the IC-705 are easy to find and follow the same standard Icom user-interface workflow.

Having less front faceplate real estate, the IC-705 has less buttons than the IC-7300––about 11 less than its big brother, to be exact. However, the twin passband, gain, multi-function knob and encoder are in the same positions and layout as on the IC-7300.

And if you’ve never used an IC-7300 before, no worries: this is one of the more user-friendly interfaces you’ll find on a ham radio transceiver.

The build of the IC-705 is excellent. It’s not exactly hardened for the elements––there is no waterproof rating or dust rating, for example––but it gives the impression of a solid little radio, likely to withstand a bit of less-than-delicate handling. Yet even though it’s designed to be a portable field radio, I’ll admit that the front panel and especially the color touchscreen feel a little vulnerable. I do worry about damaging that touchscreen while the radio travels in my backpack.

The Icom LC-192

On the topic of backpacks, Icom released a custom backpack (the LC-192) specifically for the IC-705, Icom AH-705 ATU, antennas, and accessories. I did not consider purchasing this backpack, although I’m sure some operators would appreciate it, as it has dedicated compartments for supplies and the radio can be attached to the floor of the backpack’s top compartment. Again, I passed because I’m a bit of a pack fanatic and tend to grab gear that’s more tactical and weatherproof.

IC-705 and Elecraft T1 ATU at Toxaway Game Land

While its in my Red Oxx or GoRuck backpack, I house the IC-705 in a $14 Ape Case Camera insert. Eventually I want to find a better solution, but this does help pad the IC-705 while in my backpack and certainly fits it like a glove––hopefully protecting that touchscreen.

A number of third-party manufacturers have designed protective “cages” and side panels for the IC-705, but I’ve been a bit reluctant to purchase one because I feel they may add too much weight and bulk to the radio.

To the field!

Sandy Mush State Game Land

The day after I received my Icom IC-705, I took it to the field to activate Sandy Mush State Game Land for the Parks On The Air (POTA) program. Typically, when I review a new radio, I spend a few hours with it in the shack before taking it to the field. In this case, however, I felt comfortable enough with the IC-705 user interface, so I decided to skip that step entirely––I was eager to see if this little radio would live up to expectations.

The previous evening, I’d connected the IC-705 to my 13.8V power supply, so the BP-272 battery pack was fully-charged and attached to the IC-705. There was no need for an external battery to be connected.

[Tip: Click here to view my YouTube playlist of field activities with the IC-705.]

Getting on the air that day was very straightforward; indeed, the set-up couldn’t have been more simple: radio plus antenna. I connected the IC-705 to a Vibroplex EFT-MTR end-fed 40, 30, and 20-meter resonant antenna, thus an external antenna tuner was not required.

The Vibroplex/End-Fedz EFT-MTR antenna

Next, I plugged in the included speaker/mic, spotted myself to the POTA network, and started working stations. I asked for audio reports and all were very positive using only the default audio settings. Obviously, the small hand mic works quite well. I did quickly decide to unplug one of the two connectors of the speaker mic (the speaker audio side) so that the received audio wouldn’t be pumped through the hand mic, using the much better IC-705 front-facing speaker.

In the field that day, I had a few objectives in mind:

  • See how well the supplied hand mic works for SSB contacts, thus intended to ask for audio reports
  • Check out full break-in QSK operation in CW mode
  • Measure exactly how long a fully-charged Icom BP-272 Li-ion battery pack would power the IC-705 under intense operation

SSB

SSB at Lake Norman State Park

I was very quickly able to sort out how to record and use the voice memory keying features of the IC-705. There are a total of eight memory positions that can be recorded to the internal microSD card. It’s very simple to use one of the memories in “beacon” mode––simply press and hold one of the memory buttons and the recording is transmitted repeatedly until the user presses the PTT to disengage it. This is incredibly helpful when calling CQ; I typically set mine to play “CQ POTA, CQ POTA, this is K4SWL calling CQ for Parks On The Air.” I’ve also set a five-second gap between playback, allowing for return calls. As I’ve mentioned before, voice-memory keying is incredibly useful and saves one’s voice when calling CQ in the field.

The voice and CW-memory keying features of the IC-705 are robust enough that they could be used in a contest setting to automate workflow. One important note: voice-memory keying saves recordings to the internal MicroSD card. If that card is removed, formatted/erased, or if the file structure is altered, the voice-memory keyer will not recall recordings.

CW

CW at South Mountains State Park

Next, I plugged in my paddles and started calling “CQ POTA” in CW.

As with the voice-memory keyer, CW-memory keying was incredibly easy to set up. Once again, the user once has eight memory positions. As the keyer plays a pre-recording sequence, the IC-705 will display the text being sent.

One of the questions I’m asked most by CW operators about the IC-705 is whether the radio has audible relay clicks during transmit/receive switching. Radios with loud relay clicks can be distracting. My preference these days is to operate in full break-in QSK mode, meaning, there is a transmit/receive change each time I form a character––it allows me space to hear someone break in, but results in much more clicking.

The IC-705 does have relay clicks, but these are very light––equal in volume to those of other Icom transceivers, neither louder nor softer. These clicks, fortunately, are not too distracting to me, and to be fair, I find I don’t even notice them as I operate. With that said, transceivers like my Elecraft KX2 and Mission RGO One use PIN diode switching, which is completely quiet.

Battery Life

Tapping the battery icon will open a larger battery capacity monitor.

My third objective at the first field outing was to test how long the Icom BP-272 Li-ion battery pack would power the IC-705 while calling CQ and working stations in both SSB and CW for an entire activation.

After nearly two hours of constant operation, the BP-272 still had nearly 40% of its capacity.

I didn’t expect this. I assumed it might power the IC-705 for perhaps 90 minutes, max. Fortunately, it seems at 5 watts, one BP-272 could carry you through more than one POTA or SOTA (Summits On The Air) activation. I was pleasantly surprised.

Four months later…

POTA activation at Tuttle Educational State Forest

Since that initial field test, I’ve taken the IC-705 on easily thirty or more individual POTA activations. I’ve also used it at home to chase POTA stations and rag chew with friends.

In short, I’ve found that the IC-705 is a brilliant, robust portable transceiver for SSB and/or CW and a pleasure to operate.

Herein lies the advantage of purchasing a radio from a legacy amateur radio manufacturer: it’s well-vetted right out the door, has no firmware quirks, and is built on iterations of popular radios before it.

I’ve found that IC-705 performance is solid: the receiver has a low noise floor, the audio is well-balanced, the AGC is stable at any setting, and it’s an incredibly sensitive and selective radio.

Digital modes

POTA activation at Lake Jame State Park

One huge advantage of the IC-705 is that it, like the IC-7300, has a built-in sound card for digital modes. This eliminates the need for an external sound card interface. After you’ve read the installation guide, and installed Icom’s USB drivers, simply plug the IC-705 into your computing device via USB cable and you can directly control the ‘705 with popular applications like WSJT-X.

I have not used the IC-705 for digital modes while in the field, but I have done so in the home shack. It was one of the easiest radios I’ve ever set up for FT8 and FT4.

I’m not the biggest digital mode operator, but if you are into it, I expect you’ll be very pleased with the IC-705. It must be one of the most portable, uncomplicated transceivers for digital mode operation currently on the market. I know a number of POTA activators have been using the IC-705 for FT8 and FT4.

D-Star

Being perfectly honest here, I have a chequered history with the D-Star digital voice mode. I purchased an Icom ID-51a and D-Star hotspot several years ago because a local ham pretty much convinced me it was the coolest thing since sliced bread.

And in truth? It is rather amazing.

But at the end of the day I had to admit to myself that I’m an HF guy, and found the user interface and operating procedures just a bit too other-worldly. I kept the ID-51a for perhaps a year, then sold it, along with the hotspot.

Although I knew the IC-705 had D-Star built in, I really hadn’t given it a second thought. But since I’m a reviewer, I simply had to check it out. I still had my D-Star credentials from some years ago, so I set up the IC-705 and connected the transceiver to the Diamond dual band antenna on top of my house.

Fortunately, I was able to hit our only local D-Star repeater and connect on the first go. Note that, like the ID-51a, the IC-705 can use your GPS coordinates, then automatically find the closest D-Star repeater and load the frequency and settings from the default database on the IC-705 MicroSD card.

After reviewing a YouTube video demonstration, I was on the air with D-Star and found the user interface much easier to use than that of the ID-51a. It really helps having a large touch screen.

I’ll admit it: I’m warming back up to D-Star, and I have the IC-705 to thank for that.

Some day, I plan to use D-Star on HF, as well. I acknowledge that it might take some pre-arranging, but perhaps I could even make a D-Star POTA––or better yet, SOTA––contact, if the stars align. It’s certainly worth the experiment.

Let’s talk about broadcast listening

Radio Exterior de España’s interval signal on the IC-705’s waterfall display

Although I’m a pretty active ham radio operator, I’m an SWL and broadcast listener at heart. One of the appealing things about the IC-705 is its excellent receiver range (0.030-470.000 MHz) and multiple operating modes, as well as its adjustable bandwidth.  Broadcast listeners will be happy to know that the AM bandwidth on the IC-705 can be widened to an impressive 10 kHz, which is certainly a stand-out among general coverage transceivers.

After turning on the IC-705 for the very first time, I tuned to the 31-meter band and cruised the dial. I felt like I was using a tabletop receiver: for such a small transceiver, the encoder is on the large side, and the controls are ergonomically designed. The spectrum display and waterfall are amazingly useful.

The front-facing speaker on the IC-705 is well-designed for audio clarity on the ham radio bands. It’s not a high-fidelity speaker, but it’s adequate and has enough “punch” to perform well in the field. Speakers on portable QRP radios are typically an afterthought and are terribly compromised due to space constraints within the chassis. The IC-705’s speaker design feels more deliberate, akin to what you might find on a mobile VHF/UHF rig. Broadcast listeners, in other words, will certainly want to hook the IC-705 up to an external speaker––or, better yet, use headphones––for weak-signal work.

While the received audio isn’t on par with a receiver like the Drake R8B, it’s pretty darn good for a portable general coverage transceiver. The audio is what I would call “flat,” but you are able to adjust the received audio in EQ settings to adjust them to your taste. Audio is well-tailored for the human voice, so I’ve found weak signal IDs are actually easy to grab on the air.

Audio samples

One of the brilliant things about the IC-705 is the fact that it has a built-in digital recorder. Both transmitted and received audio can be recorded in real time and saved to a removable MicroSD card. I made audio recordings of two broadcast stations on the 31-meter band as samples: the Voice of Greece (9420 kHz) and Radio Exterior de España (9690 kHz). The Voice of Greece was moderately strong when I made the recording and Radio Exterior was quite strong. Click on the links to download the .mp3 files for each recording:

Voice of Greece

Radio Exterior de España

I’ve also used the built-in digital recorder to record long sessions of my favorite shortwave, AM, and FM stations. Even with the recorder on, I can typically achieve hours of listening on one battery charge and need no other power supply.

Want more audio samples?
Check out our survey results from an Icom IC-705 blind audio test.

In short? The IC-705 makes for an excellent portable shortwave, mediumwave, and FM broadcast band-recording receiver.

Charging ahead…

The supplied BP-272 battery pack snaps snugly on the back of the IC-705

Power supply is always a concern when taking a transceiver on travels. Most transceivers need a 12-13.8 volt external supply, or an external battery, one that will eventually need to be charged.

This is not the case with the IC-705, because while it can be charged or powered via a 12-13.8V source, it can also be charged via a common 5V USB power supply. Simply insert any USB phone-charging cable into the MicroUSB port on the side of the IC-705, and it will charge the fully-depleted attached BP-272 battery pack in just over four hours.

Indeed, I traveled to visit family one week, and had plotted two park activations both en route and on the way back home. After my first activation, I quickly realized I forgot the supplied IC-705 power cord that I’d normally use to hook the IC-705 up to one of my LiFePo batteries. I was quite disappointed, expecting that I’d missed this opportunity.  Then I remembered USB charging: I simply plugged the IC-705 up to my father’s phone charger, and in four hours, the battery was completely recharged.

To my knowledge, there are no other transceivers that have this capability without modification. A major plus for those of us who love to travel lightly!

Summary

POTA activation at the Zebulon Vance Historic Birthplace

Every radio has its pros and cons. When I begin a review of a radio, I take notes from the very beginning so that I don’t forget my initial impressions. Here’s the list I formed over the time I’ve spent evaluating the Icom IC-705.

Pros:

  • Frequency range
    • TX: 160 – 6 meters, 2M, 70cm
    • RX: 0.030-470.000 MHz
  • Modes include SSB, CW, AM, FM, DV, RTTY
  • 4.3 inch color touchscreen that’s (surprisingly) readable in full sunlight
  • Multiple means to power/charge:
    • Icom BP-272 battery pack (supplied) for 5 watts output
      • Can be charged via 12V power supply or
      • 5V USB phone charger with standard MicroUSB plug (admittedly, I wish they would have adopted now standard USB-C rather than MicroUSB)
    • External battery for 10 watts of output
  • Top-shelf receiver performance (see Rob Sherwood’s assessment)
  • Wireless LAN connectivity that even allows for native remote control (not tested)
  • Built-in Bluetooth
  • Built-in GPS
  • Built-in Digital Recording
  • Full D-Star functionality
  • RTTY can be sent (using macros) and received/decoded natively
  • Multiple standard connection points on base for mounting (see con)
  • Supplied speaker mic is compact and has programmable buttons
  • Frequency stability is less than ± 0.5 ppm (–10°C to +60°C; 14°F to 140°F)
  • The IC-705 ships with an abridged owner’s manual; I recommend downloading the full version via Icom

Cons:

  • No internal ATU option
  • No built-in tilt stand (see pro)
  • Some minor ergonomic issues:
    • Angled speaker/mic connectors can be challenging to insert as they are too close to the recessed area behind front face, especially for those with larger fingers and/or if in chilly conditions in the field
    • MicroSD card also difficult to access––I use needle-nose pliers to remove and insert

Conclusion

POTA activation of Second Creek Game Land

I purchased the Icom IC-705 with the idea that I would review it and then sell it shortly thereafter. Much to the dismay of my (rather limited) radio funds, I find that I now want to keep the IC-705…indefinitely.

I didn’t think the IC-705 would fit into my QRP field radio “arsenal” very well because I tend to gravitate toward more compact radios that I can easily operate on a clipboard on my lap when necessary. My Elecraft KX2 (TSM November 2016), Elecraft KX1, LnR Precision LD-11 (TSM October 2016), and Mountain Topper MTR-3B probably best represent my field radio interests.

But I’m loving the versatility and overall performance of the IC-705. It’s providing an opportunity to do much more than most of my QRP radios allow.

Here are just a few of the things I’ve done with the IC-705 thus far:

  • Activated numerous parks in SSB and CW
  • Connected to a local D-Star repeater and talked with a fellow ‘705 owner in the UK
  • Listened to ATC traffic (and recorded it)
  • Listened to NOAA weather radio
  • Listened to and recorded local FM stations
  • Enjoyed proper FM DXing
  • Recorded GPS coordinates during a POTA/WWFF activation
  • Made numerous digital mode contacts by connecting the IC-705 directly to my Windows tablet
  • Made a 2-meter SSB contact

POTA activation of the Blue Ridge Parkway

Indeed, there are more features on this transceiver than I can fully cover in one review; truly, I consider that a very good thing.

So if you’re looking for a portable transceiver that can truly take you on a deep dive into the world of QRP HF, VHF, UHF, and even satisfy the SWL in you, look no further than the Icom IC-705.

Well played, Icom.

More Icom IC-705 articles, information, and resources:


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VisAir HF DDC/DUC Transceiver: Randy purchased one exclusively for shortwave radio listening

Many thanks to SWLing Post contributor, Dan Robinson, who recently shared a message he received from his friend Randy regarding the VisAir HF DDC/DUC Transceiver:

I recently acquired a VisAir transceiver from Russia. It is an amazing SDR unit developed by two amateur radio operators. It is about the same size as the RDR55, but at about 1/3 the cost. While it does not have FM or amateur 2/6 meter, GPS, and a couple of features, this VisAir has other features not found on the RDR55 such as dual receivers, waterfall, receiving audio equalizer, CW decoder, etc. It is a true SDR receiver. The user manual was in Russian and I had to break it into thirds so that I could get it translated into English. Interestingly, the user interface is completely in English despite its Russian origins. While designed primarily for amateur radio operators, it works especially well on the shortwave bands.

[…]I have really been enjoying this “transceiver” and as you imagine, I use only the receiver portion of the unit. It has two antenna connectors and you can configure these however you prefer. I set one as a receive antenna and the other as a transmit antenna to avoid accidentally hitting the antenna match or some function and sending power into my equipment. I also disabled the transmitter portion to further protect against any accidental transmissions.

Unfortunately, virtually all the YouTube videos and information are in Russian and also its use is shown only on the amateur radio bands, but I can tell you that this is a very nice SW DX receiver with lots of interesting user defined menus whereby the unit can be modified to match the user’s preferences. Here is a website with some information on the unit.

As you know, I have enjoyed using a wide variety of communications receivers from simple beginner’s units to the more complex and highly esteemed units built to exacting standards for government use. This VisAir is built by two guys in Russia and amazingly it was designed by them in 2017 and not a whole team of design engineers such as found at Yaesu, Kenwood, and Icom. From what I understand, the unit sells in Russia in rubles for the equivalent of about $1800 USD. Unfortunately it is not exported to the USA and it only comes with a 220 VAC power supply and so I operate it exclusively off of DC current without any issue. It is my understanding that this low production transceiver has sold between about 200 – 300 units and virtually all of these were in Russia. To my knowledge, I am the only person in the USA with this unit. Further, it is my understanding is that there is a wait list of about 2 years to obtain the unit. The VisAir is upgraded via firmware and my unit has the latest firmware installed.

When I got information about the transceiver to consider for purchase, there was only a Russian user manual available. I have access to an online PDF translator, but it can only accept up to 10 MB files and so I had to break the Russian manual into 3 sections, translate each section into English, and then stitch the 3 sections back together to make a complete English manual (which is too large to email as a whole). Attached are sections 2 and 3 of this English user manual for the VisAir:

You can look at the manual and see what features are available with this transceiver. While the translator worked nicely overall in getting the manual from Russian into English, there are issues whereby the illustrations have Russian language information and these did not translate, but this did not thwart me from understanding and using the VisAir as most of the Russian information relates to connecting the transmitter to microphone and other devices.

As with most all low production units from small producers, the user manual is good at pointing out controls, but lacks in explaining what is the purpose of settings or offering suggestions on the settings other than telling you what is a “default” setting from the factory. I found this same dilemma with the manuals for the Fairhaven RD500, the Reuter RDR55, the Kneisner & Doering KWZ30, etc. But an experienced DXer can generally figure out operations and establish the appropriate settings with a little time. For the first 3 days of operation, it was a discovery for me as I kept learning about new features that I didn’t know about previously and weren’t highlighted in the user manual. It was like reading the user manual for my Toyota Highlander in that there are options and controls that are found in menus and not particularly obvious at first glance or with casual use.

Randy

Thank you, Randy, for sharing your comments about the VisAir transceiver here on the SWLing Post. Looks like a fascinating tabletop SDR.

Click here to check out VisAir’s website.

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Guest Post: Using Carrier Sleuth to Find the Fine Details of DX

Many thanks to SWLing Post contributor, Nick Hall-Patch, for sharing the following guest post:


Using Carrier Sleuth to Find the Fine Details of DX

by Nick Hall-Patch

Introduction 

Medium wave DXers are not all technical experts, but most of us understand that the amplitude modulated signals that we listen to are defined by a strong carrier frequency, surrounded on either side by a band of mirror image sideband frequencies, containing the audio information in the broadcast.

Most DXers’ traditional  experience of carriers has been in using the BFO of a receiver, using USB or LSB mode, and hearing the  decreasing audio tone approaching “zero beat” of the receiver’s internal carrier compared with the DX’s carrier frequency as one tuned past it.  This was often used as a way of detecting that a signal was on the channel, but otherwise wasn’t strong enough to deliver audio.  Subaudible heterodynes,  regular pulsations imposed on the received audio from a DX station, could indicate that there was a second station hiding there, with a slightly different carrier frequency,  And, complex pulsations, or even outright low-pitched tones could indicate three or more stations potentially available on a single channel.

With the advent of software defined radio (SDR) within the last 10 years or so, the DXer has also been able to see a graphical representation of the frequency spectrum of the carrier and its associated sidebands.  (Figure 1)  Note that the carrier usually remains stable in amplitude and frequency, unless there are variations introduced by propagation, but that the sidebands are extremely variable.

Figure 1

Figure 2

In addition, by looking at a finer resolution of the SDR’s waterfall display, one might see additional carriers on a channel that are producing heterodynes (audible or sub-audible) in the received audio (Figure 2).  Generally speaking, a DX signal with a stronger carrier will be more likely to produce readable audio, although there are exceptions to that rule.

Initially, DXers wanted to discover the exact frequency of their DX, accurate to the nearest Hertz.  Although only a small group of enthusiasts were interested, they have produced a number of IRCA Reprints (https://www.ircaonline.org and click the “Free IRCA Reprints” button) over the years under the topic of “precision frequency measurement” (e.g. T-005, T-027, T-031, T-079, T-090) describing their use of some reasonably sophisticated equipment for the day, such as frequency counters.

So, why would this information be at all important?  In effect, the knowledge of the exact frequency of a carrier was used to provide a fingerprint for a specific radio station.    Usually, this detail was used by DXers who were trying to track down new DX, and wanted to determine whether a noisy signal was actually something that had been heard before, so would not waste any more time with it.  The process of finding this exact frequency has since been made much easier by being able to view the carrier graphically in SDR software, assuming that the SDR has been calibrated before being used to listen to and record the DX.   Playing back the recorded files will also contain the details of the exact frequency observed at the time of recording.  And, because the exact frequency of DX has become much easier to determine using SDRs, more and more DXers seem to be using this technique.

At present, Jaguar software for Perseus is the one being used by many to determine frequency resolution down to 0.1Hz, both in receiving and in playback.   But, if you have recorded SDR files from hardware other than Perseus, it is possible to get that resolution also, using software called Carrier Sleuth, from Black Cat Systems, available for both Mac and Windows, at a cost of US$20.

This software will presently take as input, sets of RF I/Q files generated by SpectraVue, SdrDx, Perseus (which includes files recorded by Jaguar), Studio One / SDRUno, Elad, SDR Console, and HDSDR.  It then outputs a single file with a .fft extension, that provides the user with a set of waterfalls, similar to those displayed by SDR programs.  The user decides ahead of time which frequency or set of frequencies (including all 9kHz or all 10kHz channels) will be output, and these will be displayed as individual waterfalls. one for each chosen frequency.  These waterfalls can be stepped through from low frequency to high frequency, or chosen individually from a drop down menu.

Let’s start by looking at a couple of output waterfalls and work out what can be done with them, then step back to find out how to generate them, and what other data is available from them.  Finally, we’ll do a quick comparison with two other programs that can produce similar output, and discuss the limitations in all three programs.

Example outputs from Carrier Sleuth

An example showing the original intent of Carrier Sleuth, determining precise carrier frequencies, is shown in Figure 3, a waterfall from 1287kHz on the morning of 28 November 2020.  At 1524UT, a woman mentions “HBC” and “Hokkaido” in the original recording, so, it’s JOHR, Sapporo.   Although there are a number of vertical lines representing carriers in this graphic, only one has a strong coloration, indicating at least 25dB more strength than any other carrier at the time of the ID, and about 50dB more than the background level.     The absolute values of time, signal strength, and carrier frequency precise to 0.1Hz, can be found by mousing over the desired point in the waterfall and then reading the numbers in the upper right corner of the display, (encircled in Figure 3).  In this case, the receiver’s reference oscillator had been locked to an accurate 10MHz clock, disciplined by GPS, so the frequency indicated in the software is not just precise, but should also be accurate.   Similar accuracy could be obtainable by the traditional method of calibrating the SDR to WWV on 10 or 15MHz.

Carrier Sleuth indicates 1287.0002kHz, within 0.1Hz of that observed by a contributor to the MWoffsets list about 7 weeks earlier (https://www.mwlist.org/mwoffset.php?khz=1287). If you look closely, there is a slight wobble on the frequency, but the display is precise enough that it can indicate that, despite the wobble, JOHR does not wander away from that frequency of 1287.0002kHz.

Figure 3

But let’s face it, tracking carriers to such accuracy is a specialist interest (though admittedly, the medium wave DXing hobby is full of specialist interests, and this one is becoming more mainstream, at least among Jaguar users).  However, if I played back a file from another morning, and found a strong carrier on a slightly different frequency from 1287.0002kHz, it might be an indication that some new Chinese DX was turning up, and that the recorded files would be worth a closer listen at that particular time.

Figure 4

In fact, I’ve found Carrier Sleuth to be useful in digging out long haul DX after it’s been recorded, as both trans-Arctic and trans-Pacific DX at my location in western Canada can be spotty at the best of times.  This means spotty as in a “zero to zero in 60 seconds” sort of spotty, because a signal can literally fade up 10 or 15dB to a readable level in 20 seconds, perhaps with identifiable material, then disappear just as quickly.   My best example so far this season was on 1593kHz, early in the UTC day of 16 November 2020, when a Romanian station on that channel paid a brief visit to my receiver in western Canada.  An initial inkling of that showed up in a Carrier Sleuth waterfall, a blotch of dark red at 0358UT, and indicated by the yellow arrow in Figure 4; that caused me to go back to the recorded SDR files that had generated these traces.

The dark blotch indicates a 10dB rise and fall in signal strength including about 60 seconds of rough audio, which turned out to be the choral version of the Romanian national anthem (RCluj1593.wav).  That one carrier and another one both started up at 0350UT, the listed sign-on time for Radio Cluj, which does indeed begin the broadcast day with that choral anthem.   Which one of the Radio Cluj transmitters was heard is still an open question, due to the lack of carrier sleuths (computerized or otherwise) on the ground in Romania,  but the more powerful one listed is a mere 15kw, so I will take either.

Finally, for those who have interest in radio propagation, the Carrier Sleuth displays can reveal some odd anomalies, for example, Figure 5 which displays both Radio Taiwan International (near 1557.000kHz on 28 November, but varies from day to day), and CNR2 (1557.004kHz)  carriers as local sunrise at 1542UT approached in Victoria, BC.

Figure 5

The diffuseness of the carriers is striking, as is their tendency to shift higher in frequency at local sunrise.  This doesn’t seem to be some strangeness in the original SDR recording, as there appear to be unaffected weak carriers on the channel.  For comparison, Figure 3 shows the same recorded time and date, but on 1287kHz, and JOHR’s carrier is pretty stable, but there are others on that channel that show the shift higher in frequency around local sunrise.  As one goes lower in frequency, these shifts became smaller and less common on each 9kHz channel, and disappear below about 1000kHz.    On later mornings, however, the shifts could be found right down to the bottom of the MW band.  Certainly, these observations are food for further thought.

Many of the parameters in Carrier Sleuth are adjustable by the user, for example, the sliders at the top of the screen can allow adjustment of the color palette to be more revealing of differences in signal strength.   The passband shown is also easily changed, and in fact, setting  the passband width to 400Hz, instead of my usual 50Hz , and creating another run of the program on 1557kHz, shows very clearly the sidebands of the “the Rumbler”, a possible jammer on the channel  (Figure 6).  Incidentally, a lot of the traces around 1557.000kHz in Figure 5 may well be part of “the Rumbler” signal as well, as filtering of the audio doesn’t seem to improve readability on the channel.

Although the examples here are taken from DXing overseas signals from western Canada, there is no reason why similar techniques may  not be applied to domestic DXing, particularly during the daytime, when signals can be weak, but can fade up unpredictable for brief periods.

Figure 6

How to create these waterfall displays in Carrier Sleuth?

So, how can you get these displays for yourself?  A “try before you buy” version of the program is available at http://blackcatsystems.com/software/medium_wave_carrier_display_app.html  and both the website and the program itself contain a quite detailed set of instructions.    However, the 25 cent tour can be summarized this way:

You start with a group of supported SDR data files, previously recorded, and use “Open I/Q data files” in the File drop down menu. Figure 7 shows the window that will open to allow you to choose any number of the files from your stored SDR files, by clicking the Add Files button  circled in red.  Then choose one of the options inside the green circle in Figure 7.  They are explained in more detail in the help write up; note that the “Custom Channel” can be specified to considerably more precision than just integer kHz values, e.g. 1205.952     The rest of the settings you will probably adapt to your needs as you gain experience.   Finally, set an output file name using the Set Output File button, and hit the “Process” button at the bottom of the window. There are a couple of colored bars in the upper right hand corner of the display that indicate progress, along with number of seconds left, although these are not always visible.

Figure 7

The generation of these waterfalls takes time.   A computer with a faster CPU and more memory will speed things up.  There is, however, an important limitation of the program.  It is specified for 32-bit systems, and although it will run with no problem on 64-bit systems, individual input I/Q files are therefore restricted to 2GB or less.   Many SDR users now choose to create larger files than this, and Carrier Sleuth will not handle them.  Another possible limitation can occur when processing 32M FFTs, which are useful for delivering very fine frequency resolution of the carriers displayed.   The program really requires in excess of 4GB of memory to handle the computation needed to deliver this fine a scale.  Unfortunately, both the 2GB file size limitation and insufficient memory limitation deliver generic error messages, followed by program termination, which leaves the inexperienced user none the wiser about the true problem.

This might be a good place for a word about FFT size and Resolution Bandwidth (RBW).  The FFT is a mathematical computation that takes as its input the samples of digital data that an SDR generates (or those samples that  have been saved in recorded files), and generates a set of “bins”, which are individual numbers representing signal strength at a defined number of consecutive frequencies spaced across the full bandwidth being monitored by the SDR. You could think of these bins as a series of tiny consecutive RF filters, spread across the band, each delivering its own signal strength.   As we are trying to look at fine scale differences in frequency when using a program like Carrier Sleuth, it is important that these little “RF filters”, or bins, each have a very narrow bandwidth.  This value is called “Resolution Band Width” (RBW), and preferably should be a fraction of a Hertz to get displays such as those shown in Figures 3 through 5.

The “FFT Length” is the number of bins that the FFT display contains, and is equal to the number of I/Q samples (either from the SDR or recorded file) that are used for the input to its computation.  The relationship between FFT Length, the bandwidth of the SDR or of the original recorded I/Q file, and the RBW is fairly simple:

Because the MW DXer is usually looking at data with 1MHz or more bandwidth, this equation tells us that to get a smaller than 1Hz RBW, we will need to have an FFT length of well over  one million bins, so it would be wise to use an FFT length at least 8M(illion).   If you are looking at a recorded file that is from an SDR using a lower bandwidth, then a lower FFT length will do the job to get a smaller RBW.

A downside of using a long FFT length is that the time resolution of the FFT becomes poorer, resulting in a display in Carrier Sleuth that will appear to be compressed from top to bottom compared with what was seen when recording the SDR file, and with correspondingly less response to fast changes in signal strength.   However, using a 16M FFT Length on a recording of the MW band results in a time resolution of about 12 seconds, so it should not be a deal breaker for most.

Producing signal strength plots 

A further specialist activity for some DXers is recording signal strength on specific channels, and then displaying the progress of signal strength versus time, often to indicate when openings have occurred in the past  (say, at transmitter sunset),  and perhaps allowing one to predict such openings in the future.    But, the world has come a long way from the noting down of S-meter readings at regular time intervals, both in deriving signal strength and in plotting the results.  Read on for an example.

Figure 8

Carrier Sleuth recently added the capability of creating files containing signal strength versus time for specified frequencies, and, depending on the size of RBW, to deliver that signal strength as observed in a passband as narrow as 0.05Hz, or as wide as 10Hz.   The program extracts the signal strength information from one of the FFT files that it has already generated from a selection of SDR I/Q files.   In Figure 5, two stations’ signals, from Radio Taiwan International, and from CNR2, were featured in the display.   With roughly 4Hz difference between the two signals, it is easily possible with Carrier Sleuth to derive signal strength from each one, specifying a bandwidth of, say 1.2Hz, to account for the propagation induced drifts and smearing of the carriers, not to mention any drift in either the receiver or transmitter.

The program creates a .csv file (text with comma delimiters) of signal strength versus time for all the frequencies chosen from an individual FFT file, but does not plot them.  There are several programs that can create plots from CSV files   For example, an Excel plot generated from Figure 5 is in Figure 8, showing peaks in those signals that occurred both before and after local sunrise at 15:42UTC.   Note that the user is not restricted to the signals found on just one of the waterfalls that are found in the FFT file, but can pick and choose dozens of signals found anywhere in those waterfalls.    (Note also that one can choose locations on any waterfall where there is no signal trace, in order to provide a “background level versus time” in the finished plots, if desired)

The process used to generate this CSV file involves searching through the FFT waterfalls for signal traces that are likely candidates for adding to such a file.   On the first candidate found, the user right clicks the mouse on the trace, at the exact frequency desired; this will bring up an editable window.   The window will show the chosen frequency as well as any subsequent ones that will be chosen, then the overall selection is saved to a text file after editing, so that the user can move on to generating the CSV file.

That file is created by going to the File drop down menu, and choosing “Generate CSV File”, where the text file produced earlier can be chosen.  Once that file is selected, the CSV file is immediately generated, and can then be manipulated separately as the user chooses.

Are there comparable programs?

Displaying waterfalls in SDR programs playing back their own files is nothing new, though not that many can do it at as fine a scale as Carrier Sleuth does, and most programs are not optimized to handle such a variety of input I/Q files.

One that does read a fair number of different kinds of SDR files is the SDR Console program; this includes Data File Analyser (64-bit only) which also can display carrier tracks to a high resolution, so let’s take a quick look at what Analyser does.  If you are familiar with SDR Console, and are reasonably experienced with the way it handles your SDR or plays back files from your favored SDR software, then these online instructions https://www.sdr-radio.com/analyser will help you get started with Analyser

This program will input a group of SDR files, then display an equivalent to a single one of the waterfalls output by Carrier Sleuth, displaying the carrier traces in reverse order, with time running from bottom to top of the display. Figure 9 shows the equivalent of Carrier Sleuth’s display of the 1287kHz carrier traces shown in Figure 3.    Analyser has a convenient sliding cross hair arrangement (shown in the yellow oval) to reveal time and frequency at any point in the display, but the actual signal power available at that point must be derived from the rough RGB scale along the left hand border. Analyser is apparently capable of about 0.02Hz resolution when reading from full bandwidth medium wave SDR files, but the default is to display exact frequency only to the nearest Hertz. The “Crosshairs” ribbon item has a drop down of “High-Resolution”  which displays to the nearest milliHertz however, though that will be limited by the actual RBW of the generated display.   The graphic display can be saved as a project after the initial generation of the signal traces, which allows the user to return to the display without having to generate it all over again, equivalent to opening one of Carrier Sleuth’s FFT files.

A useful facility in Analyser is the ability to click “Start” in the Playback segment of the ribbon above an Analyser display, then mouse over and click on a signal trace; this action will play back the audio for that channel in SDR Console, at that point in time.

It is possible to generate a signal strength plot of signal strength versus time for any individual frequency in the waterfall display, and to save that plot as a CSV file (“Signal History”).   But, the signal strength is that found only in a +/- 0.5Hz passband around the chosen frequency, with no other possibilities.  If you want to generate a plot for another frequency on the same waterfall, then you will need to run the process again, and if you want a plot for another frequency in the SDR files, then you need to generate another waterfall, which, depending on your computer’s capability, could take some time.   On an i3 CPU-based netbook with 4GB of memory, it took 30 minutes to produce one frequency’s worth of traces from data files scanning three hours.  On the same machine, Carrier Sleuth could deliver all 9kHz channels in 1hr20min from the 3 hours of files.  However, it also took 1hr20min to play back just one channel in Carrier Sleuth, which is not so efficient. (further note:   Nils Schiffhauer has developed a technique to speed up Data Analyser processing, by first using Console’s Data File Editor on full bandwidth MW recorded files; details will likely appear at https://dk8ok.org)

To conclude then, SDR Console’s Analyser will produce a display of a single channel faster than Carrier Sleuth will, and will play back the audio associated with that channel, while also having the capability to plot and record signal strength for a single given frequency within that display, but only on 64-bit computers.  It can also handle SDR files larger than 2GB in size, and will run more quickly if a NVIDIA graphics card has been installed.   Analyser is also strict about sequence of files.  If there is the slightest gap between one file finishing, and the next file starting in time sequence, it regards that as a new set, that will need to be processed separately.

Where Carrier Sleuth is more useful is that once an FFT file has been generated, it is easy to quickly check multiple channels for interesting openings during the recorded time period. It can also provide very precise frequencies of carriers, and is able to generate a file of signal strengths versus time from multiple frequencies, including those frequencies that are separated by barely more than the RBW.  For the MW band, that can be near 0.1Hz, often beyond the capability of transmitters to be that stable.  See Figure 10, which shows signal strength traces from JOCB and HLQH both on 558kHz, and separated in frequency by 0.1Hz.    At 1324UTC, JOCR dominates with men in Japanese, and at 1356UTC, the familiar woman in Korean dominates, indicating HLQH.

Figure 9

Figure 10

Incidentally, another program that seems to offer a similar functionality to Carrier Sleuth and SDR Console’s Analyser is, of course, Jaguar, which has made a point of displaying 0.1Hz readout resolution when using the Perseus SDR, and in playing back Perseus files, but…only Perseus.  There is a capability called Hi-Res in Jaguar Pro that can be applied when playing back files; this also displays fine scale traces of frequency versus the passage of time.  Steve VE6WZ, sent the example shown in Figure 11, zeroing in on his logging of DZAR-1026.  As with Analyser, clicking on a certain point in the display plays back the audio at that time, but it is unclear at this point whether the display can be saved, or whether it is generated only for one individual channel, and then is lost.

Figure 11

+   +   +   +   +   +   +   +   +   +   +   +

Availability

Carrier Sleuth  http://blackcatsystems.com/software/medium_wave_carrier_display_app.html

Analyser (SDR Console)   https://www.sdr-radio.com/download

Jaguar   http://jaguars.kapsi.fi/download/ (these are the Lite versions; to unlock the Pro version, purchase is needed)

(this article first appeared in International Radio Club of America’s DX Monitor)


Many thanks, Nick. This is amazing. What a brilliant tool to find nuances of a DX signal. I can’t help but marvel at the applications we enthusiasts have available today. Thank you for sharing!

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Radio Waves: New Quantum Receiver, Virus and Distance Learning by Radio, BBC Woofferton Early Days, and Hello Morse

Radio Waves:  Stories Making Waves in the World of Radio

Because I keep my ear to the waves, as well as receive many tips from others who do the same, I find myself privy to radio-related stories that might interest SWLing Post readers.  To that end: Welcome to the SWLing Post’s Radio Waves, a collection of links to interesting stories making waves in the world of radio. Enjoy!

Many thanks to SWLing Post contributors Andrea, Kim Andrew Elliott, Dave Porter, and Phillip Novak for the following tips:


New quantum receiver the first to detect entire radio frequency spectrum (Phys.org)

A new quantum sensor can analyze the full spectrum of radio frequency and real-world signals, unleashing new potentials for soldier communications, spectrum awareness and electronic warfare.

Army researchers built the quantum sensor, which can sample the radio-frequency spectrum—from zero frequency up to 20 GHz—and detect AM and FM radio, Bluetooth, Wi-Fi and other communication signals.

The Rydberg sensor uses laser beams to create highly-excited Rydberg atoms directly above a microwave circuit, to boost and hone in on the portion of the spectrum being measured. The Rydberg atoms are sensitive to the circuit’s voltage, enabling the device to be used as a sensitive probe for the wide range of signals in the RF spectrum.

“All previous demonstrations of Rydberg atomic sensors have only been able to sense small and specific regions of the RF spectrum, but our sensor now operates continuously over a wide frequency range for the first time,” said Dr. Kevin Cox, a researcher at the U.S. Army Combat Capabilities Development Command, now known as DEVCOM, Army Research Laboratory. “This is a really important step toward proving that quantum sensors can provide a new, and dominant, set of capabilities for our Soldiers, who are operating in an increasingly complex electro-magnetic battlespace.”

The Rydberg spectrum analyzer has the potential to surpass fundamental limitations of traditional electronics in sensitivity, bandwidth and frequency range. Because of this, the lab’s Rydberg spectrum analyzer and other quantum sensors have the potential to unlock a new frontier of Army sensors for spectrum awareness, electronic warfare, sensing and communications—part of the Army’s modernization strategy.

“Devices that are based on quantum constituents are one of the Army’s top priorities to enable technical surprise in the competitive future battlespace,” said Army researcher Dr. David Meyer. “Quantum sensors in general, including the one demonstrated here, offer unparalleled sensitivity and accuracy to detect a wide range of mission-critical signals.”

The peer-reviewed journal Physical Review Applied published the researchers’ findings, Waveguide-coupled Rydberg spectrum analyzer from 0 to 20 GigaHerz, co-authored by Army researchers Drs. David Meyer, Paul Kunz, and Kevin Cox[]

Virus and distance learning by radio (1937, 1946) (AE5X Blog)

Six to eight decades ago polio was one of the most feared diseases in the US. In 1952 alone, 60,000 children were infected, 3000 died and many more were paralyzed.
The most severe outbreaks were in 1937 and 1946. My father was a victim of the 1946 epidemic, suffering minor paralysis in one leg as a child.

In 1937, many schools around the country closed, as did public pools, movie theaters and parks. But the Chicago public school system took an innovative approach.

During that period, 80% of US households contained a radio. This allowed 325,000 children in grades 3-8 to continue their education at home via radio lessons aired by six Chicago radio stations (WENR, WLS, WIND, WJJD, WCFL, WGN) that donated time for the purpose.

Program schedules for each day were printed in the morning paper. Home with more than one radio & more than one child often set up radios in different rooms so that each child could hear the appropriate grade’s lesson.

This continued for one month…until schools reopened in late September of that year.

Curriculum was developed by teachers and monitored over the air by school officials. After each episode, a limited number of teachers were available for phone calls. A large number of the calls were from parents distressed that they could not clearly receive the broadcasts.[Continue reading…]

BBC Woofferton Early Days (Ludlow Heritage News) [PDF]

Very few structures are left in the Ludlow area which can be traced back to the Second World War. However, look five miles south of the town towards the rise of the hills and a tracery of masts can be seen. Go closer, and a large building can be found by the road to Orleton, surrounded now by a flock of satellite dishes, pointing upwards. The dishes are a sign of the recent past, but the large low building was made for the war-time radio station aimed at Germany.

This little history attempts to tell the story of the British Broadcasting Corporation’s transmitting station at Woofferton near Ludlow in Shropshire during the first years of its existence. When and why did the BBC appear in the Welsh border landscape with a vast array of masts and wires strung up in the air? The story begins in 1932, when the BBC Empire Service opened from the first station at Daventry in Northamptonshire. Originally, the service, to link the Empire by wireless, was intended to be transmitted on long-wave or low frequency. But, following the discovery by radio amateurs that long distance communication was possible by using high frequency or short waves, the plan was changed. Later in the decade, the BBC expanded the service by also broadcasting in foreign languages. Although Daventry had a distinguished name in the broadcasting world, it was never technically the best place for a short-wave site, being on a hill and close to a growing town.

This article can be found in the Ludlow Heritage News: click here to download the full PDF.

 

Hello Morse: A collection of AI and Chrome experiments inspired by Morse code on Android Gboard (Google)

Developer Tania Finlayson found her voice through Morse code. Now she’s partnering with Google to bring Morse code to Gboard, so others can try it for accessible communication.

Morse code for Gboard includes settings that allow users to customize the keyboard to their unique usage needs. It works in tandem with Android Accessibility features like Switch Access and Point Scan.

This provides access to Gboard’s AI driven predictions and suggestions, as well as an entry point to AI-powered products, like the Google Assistant.[]

 


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New RX-888 MK II SDR Receiver on the Way

Jinze (Justin) Peng, developer of the high performing, high value RX-888 SDR, has just announced an improved “MK II” version.

I’ve been very pleased with my original RX-888 in all performance aspects, and it’s wideband demodulation and IQ WAV recording have opened up new DXing possibilities (small capacity hard drives need not apply :^)

The new receiver is now appearing on eBay and AliExpress.

Details:

We are pleased to announce the second-gen of RX888. RX888 mkII is the new generation of RX888 with the following improvements and enhancements:

1. Add a tunable (variable) attenuator in the HF path, which can tune from 0 to -31.5dB.

2. Change the fixed LNA of RX888 to a VGA, which gives the -10dB to +33dB range. VGA applies to both HF and VHF.

3. Use the newer generation of tuner chip R828D instead of R820T2.

4. Use an enhanced version of 64M LPF to improve image rejection further.

5. A jumper can select the internal reference clock or an external 27Mhz reference clock.

The primary motivation is giving users smaller granularity control on the RF front-end and a big dynamic range to fit the demands of both strong and weak signals receiving. The tunable range is -41.5dB to +33dB for HF and 0db to 55dB for VHF, which covers most use cases.

During the mkII development, we are working very closely with the original author of BBRF103, IK1XPV, on his new universal driver. The new driver supports RX888 and RX888 mkII now. The new driver can download here: https://github.com/ik1xpv/ExtIO_sddc. And we expect the power of open source will significantly improve the software support and the lifetime of RX888.

Guy Atkins is a Sr. Graphic Designer for T-Mobile and lives near Seattle, Washington.  He’s a regular contributor to the SWLing Post.

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Build an affordable (but stealthy) Magnet Wire Vertical Loop antenna to mitigate condo QRM

Many thanks to SWLing Post contributor, TomL, who shares the following guest post:


Magnet Wire Vertical Loop Antenna

by TomL

For those of you in a noisy condo like me, the environment does not give me many options.  I was experimenting with a YouLoop on the wooden porch with somewhat acceptable results.  For its size, it is an excellent performer, especially on the lower bands.  Here is a very interesting review of the YouLoop, including close-up pictures of the innards of the phase inverter and 1:1 balun, by John S. Huggins.  However, it is not waterproof and I was concerned about the ice and snow ruining it.  I could tape up the connectors with waterproof tape but I also wanted  something with a bigger capture area.  A magnet wire stealth antenna might be just the thing!

I just happened to have a waterproof 1:1 ATU balun from Balun Designs that I was going to use for future Amateur Radio use whenever I get around to passing the next level test; it is total overkill for what I intended to use it for.  It would make a good connection point and (this one) also acts as an RF choke as well.  One can make a 1:1 balun by buying the right Type of ferrite core and winding it yourself.  Here is just one idea from Palomar Engineers.

So I dusted it off, went to a local store to get a 100 foot spool of 26 gauge magnet wire and tested it strung up around my living room. It came out to be a rectangle about 42 feet in circumference.  Results were usable. I expected lots of noise and there is a great deal across the bands, so only the strongest shortwave stations were received. However, I was surprised by how strong the mediumwave band was and good to listen to without an amplifier.

I am ambivalent towards trying to perfectly match the impedance since this is a broadband receive-only antenna and the impedance will vary greatly over MW and SW bands.  And I don’t want to mess with a remotely controlled tuned loop since this antenna was destined for the outdoor porch.  I tried a Cross Country Wireless preselector at my desk but had some mixed results.  I later found out, by disconnecting things in series, that the preselector inline raised the noise level about 5 dBm, so I took it out for now. Perhaps it needs more internal shielding or the connecting cable is bad.

Polarization is an issue, too.  I have read that most man-made noise (QRM) is vertically polarized, so why would I use a vertically oriented loop?  Then I saw David Casler’s video on loop antennas where he explains that connecting a vertical loop antenna at the bottom or the top makes it horizontally polarized (connecting the coax on the side makes it vertically polarized).  I never knew that!  Horizontal polarization will mitigate some of the offending QRM as well as match the polarization of mediumwave band transmitters.  Furthermore, I read that a horizontal loop will have poor signal pickup at low frequencies because it is not high enough off the ground, similar to a horizontal dipole. For now, a vertical loop connected to facilitate horizontal polarization is what I want.

A note about wire size. People make a big deal about it but those are mostly amateur radio people.  Transmission depends on efficiency so things like wire size, skin effect, standing waves, and other things matter (see here, for example).  With a receive-only antenna it is OK to use very thin wire.  Resonance can matter if you want the last ounce of signal strength with an antenna tuner, like in high-Q type loops where the bandwidth is very narrow and you are using a multi-turn loop with variable capacitor and a pick-up coil of wire to the receiver.  Comparatively, my simple loop is depending more on a single turn of wire, the aperture size, length of wire for its performance, and carefully isolating the feedline coax using RF chokes at both ends.

Here is one example of a strong station from Cuba I was able to record because WLW was off the air for some unexpected reason.

Radio Reloj, Cuba 870 kHz (At the end, you can hear WLW come back online with CBS news):

Side note about Radio Reloj on Wikipedia, the strange format seems to fit well with a totalitarian regime, including a “corrector” who “corrects the content/writing errors to meet the requirements”.  Read the wiki link for yourself.  Not a society I want to live in, thank you very much!

Example of 80 meter band performance – Greetings to a new person from members of the “Awful, Awful, Ugly Net”, 3855 kHz:

Encouraged by the results, I “installed” the magnet wire around the support beams of the wooden porch, wrapping it carefully to create a square loop. Holding it in place is a brick at each bottom corner since I am not allowed to nail anything into the Association-owned porch.  The length came out to about 32 feet (8 feet per side), so I trimmed it and connected to the balun.  I also added an RF choke at the Airspy HF+ input from Palomar Engineers which helped bring noise down a couple of S-units.   That might not sound like a lot but by also shutting off the living room air filter and an AC switch with “wall-wart” AC power adapters on it, I was able to reduce the noise a little bit more.  There is still a lot of noise from the neighbors, so it is not a perfect situation.

Here are two examples of reception with the outside installation.

Gateway 160 Meter Radio Newsletter, broadcast (in AM) by WA0RCR every Saturday on 1860 kHz:

Side note about the Radio Newsletter.  I stumbled on it when using the YouLoop and found that some of the content is very interesting and informative.  Of course it is geared mostly towards amateur radio but some of the news items are of general radio interest as well. It airs 1pm Saturday through 2am Sunday, USA Central Time.  Obviously, many segments repeat during that lengthy timeframe and reception depends on propagation from Missouri.

KDDR 1220 kHz, West Fargo, ND station ID (presumably “nighttime” power of 327 watts):

The shortwave bands are still a noisy disaster but signal levels are higher compared to the YouLoop.  Only the strongest stations come in like WRMI, WHRI, Radio Espana, Radio Habana, and CRI. And I can hear the loudest amateur radio operators.

Just for grins, here is Radio Rebelde on 5025 kHz when band conditions were above average:

Another phenomenon I am looking into is the reception pattern of a vertical loop.  Less than 1/10th wavelength, the null is through the center of the loop.  At one wavelength, the null manifests in the plane of the wire loop.  They are too close to phase them but switching between two directional loop antennas might improve reception depending on frequency.  We shall see in the future.

At least for now, I have a decent mediumwave band which performs better than the useful CCrane Twin-Ferrite amplified loop antenna that was used in the (noisy) indoors, I can hear the 160 & 80 meter amateur bands better, and the reception of the strongest shortwave broadcasters are more predictable.  Not bad for four dollars of wire!


Brilliant, Tom! Again, I love how you’ve not only made an inexpensive antenna, but you’ve even done it within your HOA regulations. You’re right, too: if you’re not transmitting into an antenna, it blows the experimentation door wide open! Thank you once again for sharing your project with us.

Click here to check out all of Tom’s guest posts and portable adventures!

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Is AM synchronous detection a crucial portable radio feature?

Many thanks to SWLing Post contributor, Mike, who writes with the following question:

How important is AM Sync for a portable radio? Is it essential or a deal breaker?

That’s a great question, Mike, and one I don’t think I’ve directly addressed it here on the SWLing Post oddly enough.

Synchronous detection is actually a fairly deep topic to explore–and everyone has their own opinion–but I get the impression that you’d like a simple answer, so I’ll try to keep this as brief as possible. You might follow the comments section of this post as I’m sure some SWLing Post readers will share their thoughts on synchronous detection and how important it is for them.

So what is Synchronous Detection?

I like this concise Wikipedia answer:

In electronics, a synchronous detector is a device that recovers information from a modulated signal by mixing the signal with a replica of the un-modulated carrier. This can be locally generated at the receiver using a phase-locked loop or other techniques. Synchronous detection preserves any phase information originally present in the modulating signal. Synchronous detection is a necessary component of any analog color television receiver, where it allows recovery of the phase information that conveys hue. Synchronous detectors are also found in some shortwave radio receivers used for audio signals, where they provide better performance on signals that may be affected by fading. To recover baseband signal the synchronous detection technique is used.

How does synchronous detection help shortwave, mediumwave, and longwave listeners?

As the Wikipedia article notes above, sync detection can help “provide better performance on signals that may be affected by fading.”

In short: a solid synchronous detector can help stabilize an AM signal which then can help with overall signal intelligibility.

In some modern portable radios, at least, this could come at the expense of audio fidelity (see caveat below).

I use sync detection when the bands are rough, noisy, and QSB (fading) is affecting signals.

A good sync detector will help clean-up and stabilize the signal so that you can hear voice information with less listener fatigue. Sync detectors are also great tools for grabbing station IDs when propagation is less stable. If you have a receiver with selectable sideband synchronous detection, it can also be used as a tool for eliminating adjacent signal interference.

Caveat? Sync detectors vary in terms of quality.

The PL-880 has a synchronous detection “hidden” function. I’m sure it’s hidden because it’s so ineffective. The PL-880 is a fantastic portable, but don’t bother using the sync detector.

Many modern DSP portables sport synchronous detection, but they’re not terribly stable and the audio fidelity can take a big hit as well. Poor sync detectors can make audio sound “tinny” and narrow.

If a sync detector isn’t effective a providing a stable lock on a signal, then it’s pretty much useless. Why? If it can’t maintain a stable lock, it’ll produce very unstable shifting audio, often with the occasional heterodyne sound popping in as well. In those cases, it’s better to turn off synchronous detection.

Benchmark legacy tabletop receivers and modern Software Defined Radios (SDRs) typically have solid, effective sync detectors. Indeed, I rarely have the AM synchronous detector disengaged on my WinRadio Excalibur–that particular SDR and application enhance audio fidelity through sync detection.

I find that I use sync detection less with my Airspy HF+ Discovery and SDRplay RSPdx, for example, because the OEM applications natively does a brilliant job managing unstable signals.

In terms of portables, I’ve always considered the sync detector of the Sony ICF-2010, Sony ICF-SW7600GR, and PL-660/PL-680 to be pretty solid. I’m sure readers can suggest even more models.

Is sync detection an essential feature on a portable radio?

Not for me. But I do admit that I value the radios I own that sport a good sync detector.

For some SWLs and DXers, however? It might very well be a deal-breaker if a radio doesn’t have a sync detector, or if its sync detector doesn’t function well.

What do you think?

Is the lack of sync detection a deal-breaker for you? When do you employ sync? Please comment!

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