Category Archives: Ham Radio

Reading an interval signal in the waterfall

I’ve been doing a lot of SWLing with the new Icom IC-705. I suppose I’ve not much to post here other than to simply say: I think Radio Exterior de España‘s interval signal looks brilliant on the ‘705 waterfall. I captured this at the end of their scheduled broadcast around 22:02 UTC today.

Of course, the audio was pretty nice, too. Their interval signal is unmistakable:

I’ll admit: I’m loving the native recording capabilities of the IC-705. This came straight off of the MicroSD card. Bandwidth was set to 9 kHz.

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The HobbyPCB IQ32 transceiver fills a special niche in the ham radio world

The following review was first published in the September 2020 issue of The Spectrum Monitor magazine:


The HobbyPCB IQ32 transceiver fills a special niche in the ham radio world

This summer, I’ve been exploring the world of general coverage QRP transceivers. I’ve been taking my LnR Precision LD-11, Elecraft KX3 and KX2 into the field; and I’ve just finished a comprehensive review of the Xiegu G90. I also have a TX-500 and IC-705 arriving in the near future [update].

Yes, I’ll admit, I’m a devotee of the “all-in-one” nature of the latest model portable QRP transceivers.

Most of the QRP transceivers now on the market are products of large, popular ham radio manufacturers. Usually, a company will come up with a product concept, follow through with their market research, then design, develop, and produce the radio. In fairness, that’s an over-simplification of the process, but let’s just call it a “top down” design approach––meaning, the product idea is generated within the company, and is often based upon customer feedback.

Not all ham radio products come about this way, though. Some have more “grassroots” or collaborative origin.

The HobbyPCB IQ32

(Image Source: HobbyPCB)

I first noticed the HobbyPCB IQ32 transceiver at the Dayton Hamvention a few years ago. I checked it out carefully at their booth, and recall a crowd gathering around their table. Noting this, I decided, at a later time, I would also find an opportunity to check out the radio in more detail.

A couple of months ago, I was working on my list of General Coverage QRP Transceivers and asked for help filling in details of any radios I’d forgotten. A reader commented and reminded me that the IQ32 was, indeed, general coverage.

At this point, I reached out to HobbyPCB and asked for a loaner unit to explore for a few weeks. The company very kindly sent one my way some weeks ago, and I’ve been testing it on the air ever since.

Form factor

When I received the IQ32 package, I was surprised by how lightweight this transceiver is:  a mere 1.5 lbs (700 grams) packs it all in one compact package.

The chassis is made of aluminum and incredibly sturdy. It even includes side panel extensions to protect the front faceplate and knobs.

The IQ32 sports a 3.2″ color LCD touch-screen display large enough to contain all of the functions, a spectrum display, and even an area for text––both transmitted and received in PSK31 and CW. The display is reminiscent of the uBITX V6 I recently reviewed. It is recommended that the operator uses a blunt plastic stylus (or retracted ballpoint pen) for navigating the color screen, since several of the  menu settings, memories, and the like require some fairly precise tapping. The graphic user interface (GUI) feels a bit like what I’d expect to find on a piece of test equipment: a bit old school, but nonetheless quite functional.

The main encoder and selector knobs are lightweight and made of some sort of plastic or nylon. They work quite well––but if I owned an IQ32, I believe one of the first things I’d do is replace those with a lightweight aluminum equivalent.

As I mentioned earlier, the weight of the IQ32 is very reasonable at 1.5 lbs. I don’t think I’d even notice it packed in a backpack.

The IQ32, like the recently released Lab599 TCX-500, lacks an internal speaker. However, my unit came with a speaker microphone, which works fine.

The right side panel of the IQ32 has a toggle power switch, power amplifier connection, power port (5mm X 2.1mm, positive tip), PS2 keyboard connector, USB Type A, and a BNC antenna port. The left side has a 3.5mm I/Q Output, 3.5mm headphone jack, 3.5mm speaker/mic port,  and a 3.5mm CW key input.

The IQ32 also has two legs that can be adjusted so that the radio will prop up at a comfortable angle for operation. The legs can be a bit finicky to adjust and keep in place, so I preferred using an angled radio support I use for my Elecraft KX3.

A collaboration

The IQ32 also feels like a project joint effort, bringing to mind the old chocolate-peanut butter cup commercial of a bygone era: “My chocolate got mixed with your peanut butter!” And or, “My peanut butter got mixed with your chocolate!”

Curious about this seeming blend of radio ideas, I reached out to Jim Veach (WA2EUJ) at HobbyPCB for more information; he gave me a little history behind the IQ32.

Jim writes:

The IQ32 is the fusion of two products: the HobbyPCB RS-HFIQ, and the STM32-SDR. 

The RS-HFIQ was designed to be a 80-10M, 5W soundcard-based SDR––similar to the popular Softrock SDRs with some expansions and revisions. 

The STM32-SDR was designed to work with a soundcard-based SDR and [thus] eliminate the need for a PC and provide stand-alone operation. 

Inside the IQ32 is a mostly stock RS-HFIQ (in fact, we offered an upgrade kit so RS-HFIQ owners could go the IQ32 route) and a custom version of the STM-32 […] specifically for the IQ32.

The original development of the STM32 [began] a few years ago when PSK31 was the digital mode du jour and [the] PS2 keyboard roamed the land. The firmware team recently released the current FW, which greatly expanded the CW modes and reworked the memory structure based on user input.

And there you have it: even though this unique little rig has been around for a few years, I’m impressed that they continue to refine it and upgrade the firmware. Indeed, if the community of IQ32 users grow, they may be able to do even more.

On the air

To be clear, my intention here isn’t to conduct a comparative review of the IQ32. I simply want to convey what I’ve learned in the process of playing with the rig and trying out some of its unique features.

Immediately after unboxing the radio, I hooked it up to my main skyloop antenna, plugged in the power supply that accompanied the radio, then plugged in the handheld speaker mic.

I discovered rather quickly that the IQ32 user interface takes a different approach than any other transceiver I’ve ever tested. Instead of one main user interface window in which you navigate modes, frequencies, and perhaps alter spectrum and bandwidth settings, the IQ32 has a different screen layout for each mode. It’s as if each mode––SSB, PSK31, CW, etc.––has its own “page.”

Despite the very minimal controls, you can adjust many of the IQ32s settings, macros, and memories in a very granular way via the settings pages using a stylus for fine control of the screen. On the flip side, during operation, it can be frustrating when adjustments need to be made quickly between the AF Gain, RF Gain, CW Speed, and AGC, as they all use the same multi-function knob and switching between them requires several screen taps––not as quick a process as one might prefer.

Indeed, the IQ32 isn’t immediately as intuitive as most commercially-marketed radios.  But once you fully understand the settings and modes pages, it becomes easy to navigate. Note: I would advise any future owner of an IQ32 to read the manual in advance. I did this, and it certainly helped. I should add here that the IQ32 manual is one of the most comprehensive I’ve read––especially considering its collaborative roots.

Now, let’s talk modes.

SSB

Since the IQ32 requires a PS2 keyboard for PSK31, and optionally for CW, I tried my hand at SSB first.

After learning how to switch modes and filter settings, I hopped on the air. Instead of calling CQ, I decided instead to seek a park activator in the POTA program via the POTA spots website. Within 10 minutes, I made contact with two parks: one in Pennsylvania and one in Florida on the 40 and 20 meter bands, respectively. While both parks gave me a “5×9” report, I seriously doubt it was accurate based on their own signal strength. (Some park activators, like contesters, only give 5×9 reports.)

Still, my success in contacting these two parks told me that the mic settings were probably suitable and that the audio had enough punch on 5 watts to be heard. To confirm, I called CQ a few times and listened to my own signal at a KiwiSDR site in Maryland. The signal was about 5×5, but the audio was clear, clean, and had excellent fidelity.

Over the past few weeks I’ve worked dozens of stations across North America with the IQ32.

PSK31

One of the very unique features of the IQ32 is its ability to natively encode and decode PSK31. This was the second mode I was eager to try.

To use PSK31 on the IQ32, a PS2 keyboard (or USB keyboard with PS2 adapter) must be connected. I searched my shack in vain for a PS2 keyboard, but fortunately, my friend Vlado (N3CZ) came to the rescue and let me borrow one of his keyboards.

Again, note: IQ32 beginners should certainly plan to read the PSK31 section of the IQ32 manual prior to attempting a PSK31 QSO.  For starters, you’ll want to enter in your personal information into the tags settings so that you can use your keyboard function keys to automatically send CQs and to answer calls. The manual will also walk you through any other necessary settings.

Once I had everything set up, I started calling CQ on the 20 meter band; unfortunately I had no luck snagging a station. This had less to do with the radio and much more to do with the mode, which has, alas, fallen out of popularity since the advent of FT8. It’s a shame, really, because although PSK31 is a digital mode, it feels much more like a proper QSO than FT8, in my opinion. While I have a lot of respect for FT8, with PSK31, you can, as we hams say, “rag-chew”––a much more personal interaction.

And rag-chewing is exactly what I did. I contacted a friend, we set a sched for a PSK31 QSO, and it was, indeed, fun. The IQ32 has a screen with enough text space so that it’s easy to follow and to read. In fact, with this radio, I don’t feel like a computer is needed.

With the keyboard attached, PSK31 just works…and works quite well. I really like the way this feature has been implemented in the IQ32.

CW

Truly, the IQ32 actually has a lot to offer the CW operator. The IQ32 supports Iambic keyer modes A and B, with speeds up to 35 wpm. You can also adjust the weight of the dits and dahs. The IQ32 doesn’t support full break-in QSK, however: there is a slight delay after sending before the relay puts the radio back into receive mode. At present, this delay is not manually adjustable but is, rather, based on the selected keyer speed.

I’ve been very pleased using the IQ32 in CW mode with my Begali paddles and Vibroplex single lever paddle.

Of course, a really unique feature of this rig is that it provides the operator with the means to use the PS2 keyboard to send CW, just as you can with the PSK31. At present, there is no CW decoder, but for those who feel their fist isn’t quite up to par, you can surprise the operator on the other end by sending perfectly formed and spaced CW by simply typing it on the keyboard.  Herein lies a very unique feature and application for the IQ32.

Indeed, as a frequent Parks On The Air (POTA) field activator, I rely very heavily on memory keyers to call CQ, send a park number, as well as give my thanks and 73s to those who contact me. Using a pre-programmed message means that I then have time to log a station while it sends, and to ensure my code is cleaner when I send park numbers––especially since I don’t exactly excel at sending strings of numbers!

With the IQ32, I find I can program full CW messages to play when I simply press one of the function keys on the keyboard. This gives me much better flexibility and control than, say, the built-in memory keyer on my venerable Elecraft KX2.

With the IQ32, a CW op would actually have the choice of never even touching a key, and just sending all messages with the keyboard. While I could never see myself doing that (as I quite enjoy sending CW with a key), the flexibility of pre-programming an array of CW memory messages and having them conveniently at hand is nonetheless quite appealing.

As a CW operator, I’m quite pleased with the IQ32. My only wish would be for a slightly shorter relay hang time for use in contesting or on Field Day.

The IQ32 Niche

While I wouldn’t necessarily recommend the IQ32 as a first transceiver to a newly-minted ham, I can certainly envision a niche market for this unique rig.

For one, I think the IQ32 could satisfy those operators who desire a very clean and stable transmitter. The IQ32 sports a Class A 5-watt power amplifier with individual low-pass filters for each band that exceed FCC requirements for spectral purity. It also has a Temperature-Compensated Crystal Oscillator (TXCO) for frequency stability––truly, this is not common in a radio of this price class.

For another, the IQ32 could be used as a driver for a transverter when operating on VHF or UHF. Another of its unique and useful features is that the user can set an offset to display the transverter output frequency rather than the IQ32-driven frequency.

 

 

And, finally, let’s face it: I know of few other radios that you can take to the field, hook up a keyboard, and natively send and decode PSK-31 transmissions. My KX2 can do this to a degree, but I have to input the text as CW, and the number of characters in the display is quite limited. The IQ32 is robust enough to permit you to carry on PSK-31 rag-chews, if you wish. If this is your thing, you’ll definitely want to play with this rig.

Being able to send CW with a keyboard and pre-programmed messages also means CW operators could make their workflow much more efficient in either the shack or the field.

In conclusion, I’ll admit that the IQ32 isn’t as intuitive as other radios and that the ergonomics leave room for improvement. But it’s still a cool little radio. If, after having read this tour of the IQ32, you feel like you’re in this radio’s niche market, then definitely reach out to HobbyPCB: I’ve found their customer care and support to be absolutely benchmark.

All in all, I’ve had a lot of fun tinkering with this unique general coverage QRP transceiver; I expect others like me will, too. Many thanks to HobbyPCB and the IQ32 crew for letting me take a deep dive into this very special little rig!

Click here to check out the IQ32 at HobbyPCB.


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Taking the Icom IC-705 to the field for a battery endurance test

I recently posted results from my listening endurance test with the new Icom IC-705 QRP general coverage transceiver. I’ve been on a mission to see just how long the supplied BP-272 Li-ion battery pack can hold up with a full charge in real-world conditions.

Thursday, I took the IC-705 to the field and activated a park using only the charged battery pack. After nearly 2 hours of constant operation (calling CQ and working stations) the BP-272 still had nearly 40% of its capacity.

That’s better than I expected, especially knowing the BP-272 is the slim, lower capacity battery pack.

I have to admit: that was a particularly fun activation because propagation finally gave me a break and I worked stations from the Azores to Oregon on a mere five watts of power.

Click here to read my full field report at QRPer.com.

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Radio Waves: The “Weird Wide Web” of SW, VOA Whistleblower Complaint, KiwiSDR v RaspberrySDR, and the Portable Operations Challenge this weekend

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 Steve Lord, Michael Guerin, and the Southgate ARC for the following tips:


Propaganda, Pirates and Preachers: The Weird Wide Web Of Shortwave Radio (The Dork Web)

The world of Shortwave is a world of state-backed propaganda, cults, pirates, and spies. You’ll find every form of freakery and geekery on air. Digital, analogue, even stuff where you can’t tell if it’s digital, analogue, bad music or interference.

[…]In a world of constant connections Shortwave radio may seem anachronistic. But there’s something special in Shortwave and I’d like to show it to you. With a tiny bit of effort and at zero cost you can explore this world from the comfort of your own home.

How Shortwave Shaped Lives

Of all the things I expected to get into, Shortwave radio wasn’t one of them. As a kid I’d listen to my dad’s old valve radio. Strange voices from distant lands floated through the air. Shortwave’s audio quality was terrible even by early 80s standards. There was something magical in hearing distant voices from across Europe and beyond.

I got back into Shortwave listening earlier in the UK lockdown period. Over the past few months I’ve heard stations from as far as Florida, Cuba, Botswana, North Korea and China. I’ve heard signals broadcast from Ascension island in the Atlantic to Tinian island in the Pacific.

Some people will tell you that Shortwave is dead. While it’s passed a 20th century peak there’s plenty happening. In 2002 the National Association of Shortwave Broadcasters estimated that hundreds of millions of households around the world had Shortwave-capable receivers.[]

Six senior Trump admin officials file whistleblower complaint over Voice of America CEO (The Hill)

Six senior Trump administration officials filed a whistleblower complaint with the State Department’s inspector general over allegations that Michael Pack, CEO of the U.S. Agency for Global Media (USAGM), violated federal law and abused his authority, according to a copy of the complaint reported by Politico on Wednesday.

The 32-page complaint includes allegations from six members of the Senior Executive Services at the USAGM accusing Pack, who was confirmed as head of the agency which oversees the state-run network Voice of America in June, of engaging in conduct that “constitutes an abuse of authority and gross mismanagement.”

The six officials who filed the complaint were all placed on administrative leave Aug. 12.

The complaint alleges Pack, who was appointed by Trump, wanted to force out the complainants because they were part of the “Deep State” and had “played a role in the delay” of Pack’s confirmation to his position at the USAGM.

The complaint alleges Pack ordered a close aide to conduct research on the voting history of agency employees, including one of the complainants, Matthew Walsh, the deputy director for operations who was placed on administrative leave. The research “was to be utilized in evaluation of career civil servants’ abilities to carry out the duties of their positions,” the complaint states.[]

KiwiSDR vs RaspberrySDR— a tale of two SDRs (Hackaday via Southgate ARC)

Once you move away from the usual software defined radio (SDR) dongles, you have only a few choices unless you want to drop some serious cash. One common hobby-grade SDR is the KiwiSDR. This popular unit runs Linux and can receive up to 30 MHz. The platform uses a dedicated A/D converter, an FPGA, and BeagleBone computer. Success of course breeds imitators, and especially when you have an open source design like the Kiwi, you are going to find similar devices with possibly different end goals. That’s how the RaspberrySDR came to be. This is a very similar unit to the KiwiSDR but it uses a Raspberry Pi, along with a handful of other differences. What’s different? [KA7OEI] tells us in a recent blog post.

Other than the obvious difference of the computer and all that it entails, the RaspberrySDR has a higher speed A/D (125 MHz vs 66 MHz) and 16-bits of resolution instead of the Kiwi’s 14 bits. This combines to give the Raspberry a wider receive range (up to 60 MHz) and — in theory — better performance in terms of dynamic range and distortion.

[KA7OEI] measures a few key parameters on both devices and arrived at some surprising conclusions. The Kiwi appears to boost signals near its cutoff frequency to compensate for losses in the system. The Raspberry — using adapted software — looks as though it does the same trick, but does it around the Kiwi’s cutoff frequency, which is lower. Probably a software fix could take care of that, of course.

There are also tests of image rejection and front-end overloading. The tests revealed a few problems with signal strength measurement and some other problems with the RaspberrySDR. The biggest issue, though, was that the 16-bit A/D didn’t seem to have better performance. Without proper design, throwing more bits at a problem isn’t always helpful and this appears to be a good example of that.

In the end, the Raspberry looks like a cheap clone of the Kiwi with some benefits, but also some drawbacks. The blog post also covers some open source issues where Kiwi is now saying some parts of their code will only be binary in the future and there has been some difficulty finding all of the Raspberry’s files. If you are looking to buy one, you might not find the name “raspberrysdr” but [KA7OEI] suggests searching for “New 16bit 62M real-time bandwidth network shared SDR receiver” which does turn up some results.

Of course, you can always use a Pi with a more conventional dongle, and that works well enough. If you want to make a Pi just transmit, you can do that with little more than a wire, although the quality might not be perfect.

https://hackaday.com/2020/09/30/kiwisdr-vs-raspberrysdr-a-tale-of-two-sdrs/

Portable Operations Challenge (Southgate ARC)

The final rules for the FMH Portable Operations Challenge are now posted on the POC webpage at foxmikehotel.com/challenge/. N1MM+ users, need to select FMHPOC as the contest and VKContest Logger users just POC.

The organisers wish all other contests taking place this weekend success and lots of fun – the bands will be busy again and we’re hoping propagation plays along.

We hope many amateurs give this new-style contest a go whether from a home QTH station or out portable.

Ed DD5LP


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Icom IC-705: Let’s see how long it’ll receive with supplied BP-272 Li-ion battery pack

The shortwave radio listener part of me might actually be more excited about the Icom IC-705 than the ham radio operator part of me.

The IC-705 has a number of features for ham radio operators who also enjoy broadcast listening. For example, it sports:

  • a general coverage receiver,
  • good performance specs,
  • notch filtering (both manual and automatic),
  • Icom twin passband filtering,
  • an AM bandwidth filter maximum width of 10 kHz
  • built-in digital recording of both received and transmitted audio,
  • audio treble/bass adjustments,
  • and battery power from Icom HT Li-ion battery packs

The Icom IC-705 ships with an BP-272 Li-ion battery pack and since the announcement last year about the IC-705, I’ve been curious how long the BP-272 could power the IC-705 in receive only.

A real-world RX test

Yesterday morning, I resisted the urge to hunt POTA and SOTA stations with the IC-705 and, instead, spent the day simply listening.

I started the experiment with a fully-charged BP-272 7.4V 1880 mAh battery pack (the pack supplied with the IC-705). At 9:00 in the morning, I unplugged the IC-705 from my 12V power supply and ran the receiver all day on just the battery pack.

I made some practical changes to maximize play time: I turned on the screen saver, turned off GPS, set the LCD backlight auto adjustment to 2%, and set the screen timer to turn off after 1 minute.

I ran the volume somewhere between low and moderate and only raised it to what I would consider very loud a few times to copy weak signals. I listened to AM, SSB, and FM signals across the spectrum, but primarily cruised the HF bands.

Of course, I never transmitted with the IC-705 during this period (saving that for the next test).

I probably could have done more to decrease current drain, but frankly I wanted this to be based on how I’d likely configure the rig for use on an SWL DXpedition.

Results

I unplugged the IC-705 from the 12V power supply at 9:00 local and the radio auto shut down at 16:39 local: a total of 7 hours, 39 minutes.

Honestly? I’m fairly impressed with this number mainly because it’s based on the smaller battery pack. The supplied BP-272 pack has 1880 mAh of capacity. The optional BP-307, on the other hand, has 3150 mAh of capacity.

If I decide to keep the IC-705, I will be very tempted to purchase a ($130 US) BP-307 pack as well.

Next test: How long can the IC-705 last on battery during a POTA activation?

As early as today, I will see just how long the BP-272 pack can operate the IC-705 during a POTA activation. This will be a true challenge on the smaller battery pack since POTA activations require a lot of transmitting (constant CQ calls and exchanges). There’ll be no lack of calling CQ on a day like today when propagation is so incredible poor.

Follow the tag IC-705 for more updates.

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How to build an automatic remote antenna switch


Many thanks to SWLing Post contributor, Kostas (SV3ORA), for sharing the following guest post which originally appeared on his radio website:


How to build an automatic rig/antenna switching system

by Kostas (SV3ORA)

When I started collecting vintage rigs, I ended up in a line of rigs on my bench, that were sitting there, disconnected from any mains cables or the antenna. I wanted these rigs to be ready to fire at any time I wanted to, without having to connect/disconnect cables all the time. I also wanted to be able to compare different rigs performances at the flip of a switch, which is the only way this can be done on the HF quick fading conditions. For power cables, the solution was to leave them connected in the mains plugs all the time. My rigs that have an internal PSU, have mechanical switches, so they are isolated from the mains when they are switched off. The rigs that are powered by an external PSU, depend on the external PSU main switch for isolation (in case they haven’t mechanical switches on them), which in my case is mechanical and switches off the mains power, when the PSU is switched off.

However, for the RF cables, this was a different story. Having only one antenna and multiple rigs, means that you have to connect each rig to the antenna every time you want to operate each rig. This is not only boring and time consuming (you have to reach the back of the transceivers to connect/disconnect the connectors), but eventually causes the connectors of the coaxial cable and the rigs to wear out. I decided to make things better and make an RF rig selector for my rigs. This RF rig selector has been described in this link.

The current antenna I use is fine for transmitting, but in the noisy neighbourhood where I live, it picks up a lot of noise. I have tried many solutions, without significant effect in the noise level. This is why I decided to use a separate antenna for receiving, from that used for transmitting. This antenna will be some kind of loop probably, so as to be immune to noise or insensitive to the direction of the noise. It will be placed in a different location than the transmitting antenna, a location which will be less noisy. Unfortunately, the space I have for the TX antenna lies in a very noisy location in my property. So a separate RX antenna, in another physical location is a must. This means that a separate coaxial for the RX antenna must be used. Thankfully, the RX coaxial can be very small in diameter, passing easily through the sides of the windows, without extra holes.

To satisfy all of my requirements, I developed the circuit shown above. The circuit is able to switch a common antenna to four different rigs. Why four? Because this was the capacity of my switch and the number of connectors I had available. If you have a greater capacity switch and more connectors, expand the circuit to your needs.

The circuit of the shack switch, allows for 4 separate rigs to be selected, and two antennas, one for RX and one for TX. TX/RX antenna selection is being done automatically (split antenna operation) and controlled by the PTT of any of the rigs connected. This feature can be bypassed by the switch, so that the TX antenna can be used for both RX and TX. The same switch allows also RX operation with passive RX antennas of active ones. When in the active RX antenna position, power is passed to the remote RX preamplifier through the RX coaxial cable, using a bias-T circuit. The values of the bias-T circuit have been chosen very large, so as active RX antennas that operate at LF and lower could still be used. The RF relay defaults in the TX antenna, so that if there is a power failure, or if the circuit is not supplied with power, you can still receive (and transmit) with the TX antenna. The other way around, would be fatal for both the transceiver and the RX antenna (If you transmitted accidentally into it).

The PTT circuits are based on my transceivers. Unfortunately, there is no “standard” for the PTT circuits, each rig has its own way, so the PTT circuits must be thought for each of them. I followed an “inhibit” approach for the PTTs. That is, all the PTT switches are connected in series and DC is passed through them. If any of the rigs transmits, the PTT switch is opened and the circuit switches to the TX antenna. For the rigs that do not have an internal relay but output DC on TX instead, an additional small relay is used (for greater isolation and lossless switching). The only drawback of this “inhibit” topology is that the PTTs of all the rigs must be connected to the circuit simultaneously. If you want to exclude a rig of course, you may short circuit it’s PTT connector in the circuit. The PTT circuits as I said, are non-standard, so you might want to change the circuit to your needs, but anyway you got the idea.

Notice the connections in the circuit. One section of the RF switch (on the left) is used for the positive wire (central conductor of the coaxial) and another for the negative (braid of the coaxial). Why is that? This is because I canted to add a special feature to the switch. That is, the ability to disconnect the antenna from any rig when the rigs are not used. Previously, I used to disconnect the antenna coaxial from the transceiver when I was away, so as to protect the transceiver from antenna static discharges and possibly destroy it’s front end circuits. Now, with a single flip of the switch, I am able to do so. Because I wanted the switch to operate on different types of antennas (balanced or not) I decided to short circuit both poles of the antenna at this position, to equalize their charges.

But equalizing their charges was not enough. I had to find a way to let these charges go to the ground, so that the antenna is discharged. Directly grounding the short circuit, did not seem a good thing to do, because the whole TX wire antenna on the roof would be grounded. Whether this is a good idea to avoid lightings or not, I do not know. So I decided to keep the short circuited antenna floating and instantly discharge it only when adequate static charge is built upon it. For this purpose, I used a neon tube, permanently connected to the switch NC (not-connected) position. When the switch is in the non-connected position, the tube lights up and discharges the antenna (both poles) if an appropriate amount of static charges has been built upon it. When the switch is in any of the selected rigs connections, the tube is disconnected, preventing it from lighting up when you transmit into the antenna. Note that this configuration, requires that the output (antennas) coaxial connectors must be isolated from the metal chassis of the RF switch!

Isolation of the output antenna connectors has been done with a PVC sheet and isolated screw rings. Also note the usage of BNC connectors on TX and SMA on RX. I used BNC connectors for various reasons. They are excellent connectors with quick lock/unlock features. You do not need to screw them (and wear them out) and once fit in place they are not unscrewed. Once fitted in place, they allow for rotating the connection without unscrewing the cable or bending it. They can handle 100W easily. Despite all these features, they are much smaller in size and lighter. Their reduced size fits easily to reduced diameter cables like the RG-58 and similar. In an RF switch where there are lots of cables connected, this does make a difference. They are also very common and very cheap. There are even types that do not require soldering at all to fit a coaxial to them. I use BNC connectors even at my antenna side, as they have been proven to be quite waterproof. The types of BNC connectors I choose are not silver plated. Despite silver plated connectors are better, in the long term they are corroded by humidity and become much worst than the nickel plated connectors. The connectors I used are nickel plated with gold plated central conductors. I have found these types to be much more durable over the years, despite being cheaper. The same goes for the RX SMA connector, but I used an SMA connector there so as to accommodate thinner coaxial cables for RX.

The BNC connectors used, are the square flange types. I used this type of connectors because when they are fitted onto the chassis, they cannot be unscrewed, unlike the single-hole types. For the RX though, I used an SMA connector because it is even smaller and it can accommodate smaller diameter cables. The coaxial cable used for the internal switch connections on TX, is the RG-223. This cable is silver-plated (both the central conductor and the braid), it has double braid for increased shielding, it is of the same diameter as the RG-58 and it has a bit lower loss. The cable loss is negligible though for such small pieces of cable. The same type of cable has been used for the internal switch-relay connections as well as for the connections of the selector to the rigs. Appropriate lengths of RG-223 cables were cut and fitted with BNC connectors at one side and the appropriate rig connectors at their other side. For the RX antenna, you may use the thinner diameter cable you can find. I used a small piece of very thin coaxial (taken out of the WiFi card of an old laptop) and passed this piece through the side of the windows of the shack and through the mosquito net of the windows. No extra holes are required that way! For the rest of the RX cable, you can use whatever cable diameter you want, but I tried to use the smallest diameter I could find, so that the cable is as much phantom as possible.

All the coaxial rig cables are grounded at the connectors side. I used a piece of coaxial braid and fitted it to the connectors screws. Then I soldered the braids of the coaxial cables onto this piece. Notice the black ring screw isolators at the antenna connector, to isolate it from the chassis. Speaking about the chassis, do not use a plastic chassis for the RF switch, use only a metal one! The picture below, as well as all the next pictures, show the RF cables arrangement, but note that the circuit in these pictures is not complete yet.

The coaxial cables are soldered onto the switch contacts. Where a ground connection is required, a piece of braid accomplishes this. Do not use thin wires, the device has to allow for at least 100W of HF RF power to pass through it. I have tested the switch with 200W of power and there were no problems at all. The neon tube directly connects to the appropriate switch contact and to the chassis.

The most important part of an RF switch is of course the switch itself. For 100W of HF RF power, I would suggest you to use a porcelain switch. I had a 5-positions 4-sections small porcelain switch, which I used. I connected two sections at each side in parallel (adjacent pins connected together). That is, two sections in parallel for the positive wire and two sections in parallel for the braid. I did that for various reasons. First, by using two contacts for each connection instead of one, you increase the power handling capability of the switch. Then, you ensure a sure-contact throughout the years. Any corrosion or wearing on the switch contacts would cause contact problems eventually. By using two contacts for each connection instead of one, you double the probability for a good contact. After all, I had a switch with more sections, so why not make a good use of them?

The completed selector is shown above. The relay was been taken out of an old CB radio. Use the best quality relay you can afford, as this will be switched quite often and it must handle at least 100W of RF power.

The results from the RF switch operation are quite satisfying. The overall construction is kept small and low profile. The switch makes a good contact despite being small. The automatic discharger seems to work well. On receive, there is some RF leakage, as I expected, in the near by cables, which is noticed in the higher HF bands or in very strong signals. The very sensitive receivers we use, are able to detect that. This RF leakage occurs even when the switch is in the NC position, where the antenna is disconnected and floating. So, to be honest I have not figured out if the leakage is from the switch or from the external cables in the shack. On TX, there is of course severe leakage from the transmitting coaxial to the rest of the ports. This IS expected. There is leakage even without using any selector at all, in the nearby receivers, when a transmitter operates at such high powers. There is nothing you can do about it really, unless your receiver has a mute capability, which I did not bother to take care of.

The TX/RX switching is taken care automatically and this is very useful and relaxing for the operator as he does not have to worry about anything. The active or passive RX antenna selector and the feature to disable the auxiliary RX antenna are really useful and you can do many antenna and rigs comparisons on-the-fly with it, by the flip of a switch. Depended on the noise level and the sensitivity you want to achieve, the switch will provide you the most optimal RX conditions instantly!

The most important thing though, is that the goal of this project was achieved. I am able to switch the antenna to whatever rig I want at the flip of a switch. And before I go away, at the flip of a switch I can isolate and automatically discharge the antenna when needed. This is so much more convenient than having to connect and disconnect cables all the time. I can also now use a separate antenna for RX, which greatly improves reception in my case. This antenna is automatically switched by any rig I have and I do not have to worry about anything. I can also do comparisons between different antennas on RX, which is crucial in deciding which antenna is better for receiving. All these features make this little simple to build circuit, so useful and an integral part of the shack.


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The Icom IC-705 has landed at SWLing Post HQ

Yesterday, I received my new Icom IC-705 QRP transceiver (along with two FT-60R HTs) from Universal Radio.

I got home pretty late yesterday afternoon so haven’t had a lot of time to put the IC-705 on the air.

I did tune to the Voice of Greece and REE last night and, must say, was pretty impressed with AM mode.

This morning, I also worked two CW stations and one in SSB on the 40 meter band from my home.

Very early days, but I get the impression the IC-705 receiver is top shelf. At least, I like what I’m hearing.

So far, the only negative I’ve mentally noted is the difficulty in propping up this radio for use on a desk. It’s a little awkward. No doubt, a number of 3rd party solutions will soon emerge. I’m personally hoping someone will design a 3D printed stand/cradle.

Indeed, a 3D-printed front panel cover would also be nice because I do worry about the touch screen display being damaged in my backpack. Being a bit of a picky backpack geek, I did not opt for the custom Icom LC-192 backpack (completely subjective: just not my style and not waterproof). The IC-705 can be secured in the LC-192 so that the front panel is well-protected.

The IC-705 backlit display is very easy on the eyes–I hope it’s as easy to read in sunlight outdoors. We’ll soon find out because I’m certainly taking it to the field!

IC-705 Unboxing Photos

By request, here are some “unboxing” photos (click to enlarge):

Follow the tag IC-705 for more updates.


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