Tag Archives: FunCube Dongle Pro+

SDR Primer Part 2: Exploring the world of SDRs for $200 or less

The $22 RTL-SDR paired with a Raspberry Pi and employed as an ADS-B receiver/feeder.

The following article originally appeared in the July 2018 issue of The Spectrum Monitor magazine:


Welcome back to the world of SDRs

Last month we covered Part One of our three-part primer on software-defined radios (SDRs). While last month’s Part One focused on the nomenclature and components of a functioning SDR system, Part Two will take a look at some affordable SDR station options that will propel you into the world of SDRs for less than $200 US. We’ll cover Part Three in November, and we’ll dive a little deeper into the rabbit hole and cover higher-end SDRs and ham radio transceivers with embedded SDRs.

SDRs are affordable

Photo by Kody Gautier

If there’s one thing I’d like you to take away from this part of our primer, it’s that SDRs are truly affordable. For less than the price of a typical full-featured shortwave portable, you can own an SDR that covers almost all of the listening spectrum, and that does so with excellent performance characteristics.

We’re lucky to live in a time of phenomenal radio innovation. When I first jumped into the world of SDRs, the least expensive SDR that covered any of the bands below 20 MHz was about $500. That was only a few years ago, in 2010 or so.

Yet in the past three years, affordable SDRs have become the dominant radio product on the market.  And these modestly-priced products have made the barrier of entry into the SDR world crumble overnight.

Today, even a $100 SDR has more features, more frequency range, and more functionality than a $1000 SDR from just a decade ago.  Times have changed dramatically; indeed, the pace of innovation in this craft is simply amazing.

Before we begin looking at some choice sub-$200 SDRs, I’d just like to direct your attention to the first part of our SDR Primer (click here to read). Specifically, I’d like you to note one element I discussed in that article:  the vital importance identifying your goals as an SDR owner. In other words, how do you plan to use your SDR? If you’re only seeking an SDR to listen to local ham radio repeaters, track cubesat satellites, or gather ADS-B information from aircraft, a $25 SDR will more than suffice. If you wish to use the SDR as a transceiver panadapter, or you wish to chase weak signal DX on the HF bands, then I’d suggest you invest a bit more.

I’d also like to remind you, as I noted in the previous article, that this primer will be limited in the SDRs I highlight. The reason for this is simple:  there now exists a vast ocean of SDRs on the market (just search eBay for “SDR” and you’ll quickly see what I mean) so all models simply can’t be included in this introductory foray. I’ll be focusing here on several SDRs that cover the HF spectrum and above. I’ll also focus on SDRs with which I have personal experience, and which I consider to be “enthusiast” grade among a healthy community of users. Of course, this part of the primer will only include HF-capable receivers that cost a total of $200 or less.

Let’s take a look at what’s on the market in order of price, starting with the most affordable.

$10-$25: The RTL-SDR dongle

No doubt, many of you reading this primer have purchased an RTL-SDR dongle. Over the years, I’ve owned three or four of them and have even purchased them for friends. These dongles originally appeared on the market many years ago as mass-produced DVB-T TV tuner dongles based on the RTL2832U chipset. Very soon, users discovered that with just a little hacking, the dongle was capable of much, much more than its original intended purpose.

The dongle resembles a USB memory stick. On one end, you’ll find a standard USB connector.  On the other, you’ll find an antenna port, typically SMA, to which one connects an antenna. Although it goes without saying, here’s a friendly reminder: make sure you’re choosing an antenna to match the frequency range you’re exploring!

I’ve seen this older model of RTL-SDR being sold for $9 at Hamvention.

Early RTL-SDR dongles couldn’t cover the HF bands or lower, but many models can now cover a gapless 500 kHz all the way to 1.75 GHz.

So, what can you do with an RTL-SDR dongle?  In short, quite a lot! Here are a few of this simple device’s many applications and uses in our hobby.  It can:

  • become a police radio scanner
  • monitor aircraft and ATC communications
  • track aircraft with ADS-B decoding and read ACARS short messages
  • scan trunking radio conversations.
  • decode unencrypted digital voice transmissions such as P25/DMR/D-STAR.
  • track maritime boat positions like a radar with AIS decoding.
  • track and receive weather balloon data
  • connect to VHF amateur radio
  • decode APRS packets
  • receive and decode GPS signals
  • utilize its rtl-sdr as a spectrum analyzer
  • receive NOAA weather satellite images
  • and so much more––! This list is not fully comprehensive by any means.  Check out this list of projects at RTL-SDR.com.

And, of course, you can listen to any signals between 500 kHz up to 1.75 GHz––essentially, most of the radio listening landscape.

Is $25 still a little high for your budget? RTL-SDR dongles can be found for as low as $10 US, shipped, on eBay. While the cheapest of these dongles may suffice for some radio applications, I’m partial to the dongle produced by RTL-SDR.com, since they’re built in a tough metal enclosure, have thermal pad cooling, as well as extra ESD protection. Amazon has an RTL-SDR.com dongle starter package with antenna options for about $26. That’s, what, the price of three hamburgers? Two orders of fish and chips? And worth it.

Many third-party SDR applications support the RTL-SDR dongle, but my favorite is SDR# (click here to download).

So, the major pros of this little SDR are 1) obviously, the price; 2) many, many uses; and 3) the fact that it’s the most popular SDR on the market, with a massive online user base.

What about negatives? Well, to be frank––aside from the dongle’s budget-busting versatility––the fact is that “you pay for what you get.” You’re investing just $10-$27 in this receiver, so don’t expect exceptional performance especially on anything lower than 50 MHz. On HF, for example, the RTL-SDR could easily overload unless you employ external filtering.

Indeed, I’ve never used the RTL-SDR for HF DXing, but I currently have three dongles in service 24/7:  two as ADS-B receivers, and one as a receiver for the LiveATC network. And these work hard. Indeed, It’s a workhorse of a device!

I suggest you grab an RTL-SDR and use it as an accessible step into the world of SDRs, and as an affordable single-purpose tool to unlock the RF spectrum!

Click here to check out the RTL-SDR blog SDR dongle via Amazon (affiliate link).

$99: The SDRplay RSP1A

When you invest a modest $99 US (or $120 shipped), and purchase the RSP1A, you take a major step forward in the SDR world.

UK-based SDRplay is an SDR designer and manufacturer that focuses on enthusiast-grade, budget wideband SDRs. SDRplay designs and manufactures all of their SDRs in the United Kingdom, and over the past few years, they’ve developed a robust user community, extensive documentation, and, in my humble opinion, some of the best tutorial videos on the market.

SDRuno windows can be arranged a number of ways on your monitor.

Although the RSP series SDRs are supported by most third-party SDR applications, SDRplay has their own app: SDRuno. Moreover, SDRuno is a full-featured, customizable application that takes advantages of all of this SDR’s performance potential and features. I should mention that installing the RSP1A and SDRuno is a pure plug-and-play experience:  just download and install the application, plug in the RSP1A to your computer, wait for the USB driver to automatically install, then start SDRuno. Simplicity itself.

While the RSP1A is SDRplay’s entry-level wideband SDR, it nonetheless plays like a pro receiver and truly pushes the envelope of performance-for-price, and for other SDR manufacturers, sets the bar quite high. The RSP1A is a wideband receiver that covers from 1 kHz all the way to 2 GHz; equally pleasing the longwave DXer, HF hound, tropo-scatter hunter, and even radio astronomer. This affordable SDR really covers the spectrum, quite literally. Not only does the RSP1A cover a vast frequency range, but its working bandwidth can be an impressive 10 MHz wide and via SDRuno, the RSP1A will support up to 16 individual receivers in any 10 MHz slice of spectrum. All this for $99? Seriously? I assure you, yes.

Think of the RSP1A as the sporty-but-affordable compact car of the SDR world. It delivers performance well above its comparatively modest price, and is fun to operate. In terms of DX, it gets you from point A to point B very comfortably, and is a capable receiver which will help you work even weak signals––and very reasonably!

If you’re looking to explore the world of SDRs, would like a capable receiver with great LW/MW/HF reception to do it with, but also want to keep your budget in check, you simply can’t go wrong with the RSP1A.

Check out the RSP1A via:

$167 US (125 GBP): FUNcube Dongle Pro+

Many years ago when I ventured into the world of SDRs, one of the only affordable SDRs which covered the HF bands was the FUNcube Dongle Pro+.

The Funcube Dongle Pro+, which resembles the RTL-SDR “stick” type dongle, was originally designed as a ground receiver for the FUNcube Satellite (cubesat) project initially made possible by AMSAT-UK and the Radio Communications Foundation (RCF). The original Funcube dongle did not cover any frequencies below 64 MHz, but the Funcube Dongle Pro+ added coverage from 150 kHz to 1.9 GHz with a gap between 240 MHz and 420 MHz.

In full disclosure, I’ve never owned a FUNcube Dongle Pro+, but I have used them on several occasions. I believe you would find that it is prone to overloading if you use a longwire antenna that’s not isolated from the dongle. In other words, during such use it seems to be subject to internally-generated noise. In my experience, the Pro+ worked best when hooked up to an external antenna fed by a proper coaxial cable.

To be clear, with the advent of SDRplay and AirSpy SDRs, the FUNcube Dongle Pro+ is no longer the budget SDR I would most readily recommend.

Still, the Pro+ is a very compact dongle that has a great history, and around 2012 really pushed the performance-for-price envelope. It still has many dedicated fans. No doubt, this product has had a huge influence on all of the sub $200 SDRs currently on the market, thus we owe it a debt of gratitude.

Click here to check out the FUNcube Dongle Pro+.

$169 US: SDRplay RSP2 & RSP2 Pro ($199):

The SDRplay RSP2 Pro

In 2016, after the remarkable success of the original RSP, SDRplay introduced the RSP2 and RSP2 Pro SDRs. The RSP2 is housed in an RF-shielded robust plastic case and the RSP2 Pro is enclosed in a rugged black painted steel case. In terms of receivers and features, the RSP2 and RSP2 Pro are otherwise identical

The RSP2 and RSP2 Pro provide excellent performance, three software-selectable antenna inputs, and clocking features, all of which lend it to amateur radio, industrial, scientific, and educational applications; it is a sweet SDR for $169 or $199 (Pro version). I know of no other SDRs with this set of features at this price point.

The RSP2 series has the same frequency coverage as the RSP1A. Of course, to most of us, the big upgrade from the SDRplay RSP1A is the RSP2’s multiple antenna ports:  2 x 50-Ohms and one High-Z port for lower frequencies.

The SDRplay RSP2 with plastic enclosure.

As with all of SDRplay’s SDRs, their own application, SDRuno, will support up to 16 individual receivers in any 10 MHz slice of spectrum.

Bottom line? Since the RSP2 has multiple antenna ports––and two antenna options for HF frequencies and below–the RSP2 is my choice sub-$200 SDR to use as a transceiver panadapter. (Spoiler alert: you’ll also want to check out our summary of the recently released $279 RSPduo from SDRplay in this review or in Part 3 of our primer before pulling the trigger on the purchase of an RSP2 or, especially, an RSP2 Pro!)

Check out the RSP2 via:

$199 US: AirSpy HF+

Sometimes big surprises come in small packages. That pretty much sums up the imminently pocketable AirSpy HF+ SDR.

The HF+ has the footprint of a typical business card, and is about as thick as a smartphone. Despite this, it’s a heavy little receiver––no doubt due to its metal alloy case/enclosure.

AirSpy’s HF+ was introduced late 2017. Don’t be surprised by its footprint which is similar to a standard business card to its left, this SDR is performance-packed!

Not to dwell on its size, but other than my RTL-SDR dongle, it’s by far the smallest SDR I’ve ever tested. Yet it sports two SMA antenna inputs: one for HF, one for VHF.

The HF port is labeled as “H” and the VHF port as “V”

When I first put it on the air, my expectations were low.  But I quickly discovered that the HF+ belies its size, and is truly one of the hottest sub $500 receivers on the market! Its HF performance is nothing short of phenomenal.

The HF+ is not a wideband receiver like the FunCube Dongle Pro+ or RSP series by SDRplay. Rather, the HF+ covers between 9 kHz to 31 MHz and from 60 to 260 MHz only; while this is a relatively small portion of the spectrum when compared with its competitors, this was a strategic choice by AirSpy. As AirSpy’s president, Youssef Touil, told me,“The main purpose of the HF+ is [to have] the best possible performance on HF at an affordable price.”

Mission accomplished.  Like other SDRs, the HF+ uses high dynamic range ADCs and front-ends but enhances the receiver’s frequency agility by using high-performance passive mixers with a robust polyphase harmonic rejection structure.  The HF+ was designed for a high dynamic range, thus it is the best sub-$200 I’ve tested for strong signal handling capability on the HF bands.

You can very easily experiment and customize the HF+ as well; easy access to the R3 position on the circuit board allows you to make one of several published modifications. “During the early phases of the design,” Yousef explains, “R3 was a placeholder for a 0 ohms resistor that allows experimenters to customize the input impedance.” He goes on to provide in-depth clarification about these mods:

“For example:

  • A 300 pF capacitor will naturally filter the LW/MW bands for better performance in the HAM bands
  • A 10µH inductor would allow the use of electrically short antennas (E-Field probes) for MW and LW
  • A short (or high value capacitor) would get you the nominal 50 ohms impedance over the entire band, but then it’s the responsibility of the user to make sure his antenna has the right gain at the right band
  • A custom filter can also be inserted between the SMA and the tuner block if so desired.”

Since the introduction of the HF+, it has been my recommended sub-$200 receiver for HF enthusiasts. If you want to explore frequencies higher than 260 MHz, you’ll have to look elsewhere. Also, note that longwave reception is not the HF+’s strong suit––although modifications to R3 and future firmware upgrades might help with this! Additionally, the HF+’s working bandwidth is 660 kHz; quite narrow, when compared with the RSP series, which can be widened to 10 MHz.

AirSpy also designed the free application SDR# to take full advantage of their receivers’ features and performance.

The AirSpy application (a.k.a. SDR#)

Installing the HF+ and getting it on the air is pure plug-and-play. While SDR# is a powerful and fluid SDR application, I actually use SDR Console more often, as it supports most of my other SDRs as well, and offers advanced virtual receiver and recording functionality.

If you’re an HF guy like me, the HF+ will be a welcome addition to your receiver arsenal. It’s a steal at $200.

Click here for a full list of AirSpy distributors.

Conclusion

If you haven’t gathered this already, it’s simply a brilliant time to be a budget-minded radio enthusiast. Only a few years ago, there were few, if any, enthusiast-grade sub-$200 SDR options on the market.  Now there are quite a number, and their performance characteristics are likely to impress even the hardest-core weak-signal DXer.

Still, some hams and SW listeners reading this article will no doubt live in a tougher RF environment where built-in hardware filters are requisite to prevent your receiver from overloading. Or perhaps you desire truly uncompromising benchmark performance from your SDR. If either is the case, you may need to invest a little more of your radio funds in an SDR to get exactly what you want…and that’s exactly where I’ll take you November in the final Part Three of this SDR primer series.  Stay tuned!

Stay tuned for more in Part Three (November). I’ll add links here after publication.

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London Shortwave’s innovative PocketCHIP-powered field portable SDR

Many thanks to SWLing Post contributor, London Shortwave, who recently shared his latest SDR project: a field-portable, ultra-compact, SDR spectrum recording system based on the PocketCHIP computer.

London Shortwave has built this system from the ground up and notes that it works well but is currently limited to the FunCube Dongle Pro+ at 192 kHz bandwidth. There is no real-time monitoring of what’s being recorded, but it works efficiently and effectively–making spectrum captures from the field effortless. The following is a video London Shortwave shared via Twitter:

Click here to view via Twitter.

The PocketCHIP–the device his system is built around–is a $69 (US) handheld computer with color display:

Click here to view the PocketCHIP website.

I think this field portable SDR system is absolutely brilliant!

Homegrown innovation

London Shortwave has done all of the coding to make the FunCube Dongle Pro + work with the PocketChip computer. Even though live spectrum can’t be monitored in the field, the fact that it’s making such a clean spectrum recording is all that really matters.

All London Shortwave has to do is head to a park with his kit, deploy it, sit on a bench, read a good book, eat a sandwich, then pack it all up. Once home, he transfers the recording and enjoys tuning through relatively RFI-free radio.

A very clever way to escape the noise.

The kit is so incredibly portable, it would make DXing from any location a breeze. You could easily pack this in a carry-on item, backpack or briefcase, then take it to a park, a national forest, a lake, a remote beach–anywhere.

What I really love about this? He didn’t wait for something to be designed for him, he simply made it himself.

Thanks again, London Shortwave. We look forward to reading about your radio adventures with this cool field SDR!

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eBay Deal: Funcube Dongle Pro Plus SDR $100 shipped

eBay-FunCube

Many thanks to SWLing Post contributor, Mario Filippi, who points out this Funcube Dongle Pro Plus with a BuyItNow price of $100 on eBay.  The seller appears to have a long eBay history and a 100% rating.

FunCubeDonglePro

Mario and I were both tempted at one point to snag the Pro + at this price, but neither one of us needs another SDR.  Please, someone buy it before I change my mind and buy it in a moment of weakness! 🙂

Click here to view on eBay.

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Sean’s recording of an International Space Station EVA

ISSSean Gilbert, WRTH’s International Editor, recently shared this audio he originally recorded on June 19, 2014. Sean writes:

With all the interest in space and the ISS at the moment, I thought I would share a recording I made on 19 June 2014 @ 1715 UTC. This is from the Russian part of the ISS and the audio (which is in Russian) is of the cosmonauts talking during a spacewalk (EVA as they are known). The person speaking is actually in space, outside of the ISS. The audio begins about 2 mins into the recording and lasts for about 5 mins.

[Listen via the embedded player below, or click here for the MP3 version.]

[…]This was received on 143.625MHz NFM (+/- a few kHz due to doppler shift). Receiver here was a Funcube Dongle Pro + into a 2 element circular polarised turnstile in the attic. Signal was lost at a distance of 2000km (to the East of my location in IO92ma) at 3 degree elevation. Altitude of ISS was 418km above earth. 

Sean-Gilbert-ISS-Screen-Cap-Spectrum

The image [above] shows a grab of the signal, exhibiting doppler shift due to the ISS orbit in relation to the earth.

 […]I would be interested to know what they are saying. […]To me this was far more exciting than receiving SSTV pictures from the ISS. I may never hear another EVA – I am just thankful that I found this as it was an announced/schedules EVA.

That is very cool, indeed, Sean! At some point, I must make an effort to venture up to the VHF neighborhood and attempt to hear the ISS.

I hope there’s a Russophone reader out there who can help Sean interpret the EVA dialog! Please comment!

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Guest Post: London Shortwave’s guide to mitigating urban radio interference

London-Urban-CityMany thanks to SWLing Post contributor, London Shortwave, who is kindly sharing this guest post–a brilliant article he recently posted on his own website.

I’m very grateful: one of the most common questions I’m asked by readers is how to cope with the radio interference so many listeners and amateur radio operators experience in high-density, urban areas. If this is you, you’re in for a treat–just keep reading:


Dealing with Urban Radio Interference on Shortwave

by London Shortwave

Shortwave radio listening is an exciting hobby, but for many of us city dwellers who either got back into it recently or tried it out for the first time not long ago, the first experience was a disappointing one: we could barely hear anything! Station signals, even the supposedly stronger ones, were buried in many different types of static and humming sounds. Why does this happen? The levels of urban radio frequency interference, or RFI, have increased dramatically in the last two decades and the proliferation of poorly engineered electronic gadgets is largely to blame. Plasma televisions, WiFi routers, badly designed switching power adapters and Ethernet Over Powerlines (also known as powerline network technology, or PLT) all severely pollute the shortwave part of the radio spectrum.

Does this mean we should give up trying to enjoy this fascinating medium and revert to using the TuneIn app on our smartphones? Certainly not! There are many angles from which we can attack this problem, and I shall outline a few of them below.

Get a good radio

The old adage “you get what you pay for” certainly holds true even when it comes to such “vintage” technologies as shortwave radio. Believe it or not, a poorly designed receiver can itself be the biggest source of noise on the bands. That is because many modern radios use embedded microprocessors and microcontrollers, which, if poorly installed, can generate interference. If the receiver comes with a badly designed power supply, that too can generate a lot of noise.

So how does one go about choosing a good radio? SWLing.com and eHam.net have fantastic radio review sections, which will help you choose a robust receiver that has withstood the test of time. My personal favourites in the portable category are Tecsun PL310-ET and Tecsun PL680. If you want a desktop radio, investigate the type of power supply it needs and find out whether you can get one that generates a minimal amount of noise.

It is also worth noting that indoor shortwave reception is usually best near windows with at least a partial view of the sky.

Tecsun PL310-ET and Tecsun PL680, my two favourite portable shortwave radios.

Tecsun PL310-ET and Tecsun PL680, my two favourite portable shortwave radios.

Identify and switch off noisy appliances

Many indoor electrical appliances generate significant RFI on the shortwave bands. Examples include:

  • Plasma televisions
  • Laptop, and other switching-type power supplies
  • Mobile phone chargers
  • Dimmer switches
  • Washing machines / dishwashers
  • Amplified television antennas
  • Halogen lighting
  • LED lighting
  • Badly constructed electrical heaters
  • Mains extension leads with LED lights

Identify as many of these as you can and switch them all off. Then turn them back on one by one and monitor the noise situation with your shortwave radio. You will most likely find at least a few offending devices within your home.

Install an outdoor antenna

If you have searched your home for everything you can possibly turn off to make reception less noisy but aren’t satisfied with the results, you might want to look into installing and outdoor antenna. That will be particularly effective if you live in a detached or a semi-detached property and have a garden of some sort. Of course, you will need a radio that has an external antenna input, but as for the antenna itself, a simple copper wire of several metres will do. An important trick is making sure that the noise from inside your home doesn’t travel along your antenna, thus negating the advantage of having the latter installed outside. There are many ways of achieving this, but I will suggest a configuration that has worked well for me in the past.

Fig.1 Schematic for an outdoor dipole antenna.

Fig.1 Schematic for an outdoor dipole antenna.

I have used a three-terminal balun (positioned outdoors), and connected two 6 metre copper wires to its antenna terminals to create a dipole. I then connected the balun to the radio indoors through the feed line terminal using a 50? coaxial cable. In the most general terms, the current that is generated in the antenna wires by the radio waves flows from one end of the dipole into the other, and a portion of this current flows down the feed line into your radio. The balun I have used (Wellbrook UMB130) is engineered in a way that prevents the radio noise current from inside your house flowing into the receiving part of the antenna.

Wellbrook UMB130 balun with the feed line terminal disconnected

Wellbrook UMB130 balun with the feed line terminal disconnected

Antenna preselectors

There is a catch with using an outdoor antenna described above — the signals coming into your radio will be a lot stronger than what would be picked up by the radio’s built-in “whip” antenna. This can overload the receiver and you will then hear many signals from different parts of the shortwave spectrum “mixing in” with the station you are trying to listen to. An antenna preselector solves this problem by allowing signals from a small yet adjustable part of the spectrum to reach your radio, while blocking the others. You can think of it as an additional tuner that helps your radio reject unwanted frequencies.

Fig.2 Schematic of a preselector inserted between the outdoor antenna and the receiver

Fig.2 Schematic of a preselector inserted between the outdoor antenna and the receiver

There are many antenna preselectors available on the market but I can particularly recommend Global AT-2000. Although no longer manufactured, many used units can be found on eBay.

Global AT-2000 antenna coupler and preselector

Global AT-2000 antenna coupler and preselector

Risk of lightning

lightning

Any outdoor antenna presents the risk of a lightning strike reaching inside your home with devastating and potentially lethal consequences. Always disconnect the antenna from the receiver and leave the feed line cable outside when not listening to the radio or when there is a chance of a thunderstorm in your area.

Get a magnetic loop antenna

A broadband loop antenna (image courtesy of wellbrook.uk.com)

A broadband loop antenna (image courtesy of wellbrook.uk.com)

The outdoor long wire antenna worked well for me when I stayed at a suburban property with access to the garden, but when I moved into an apartment well above the ground floor and without a balcony, I realised that I needed a different solution. Having googled around I found several amateur radio websites talking about the indoor use of magnetic loop receive-only active antennas (in this case, “active” means that the antenna requires an input voltage to work). The claim was that such antennas respond “primarily to the magnetic field and reject locally radiated electric field noise”[*] resulting in lower noise reception than other compact antenna designs suitable for indoor use.


Interlude: signal to noise ratio

In radio reception, the important thing is not the signal strength by itself but the signal to noise ratio, or SNR. A larger antenna (such as a longer copper wire) will pick up more of the desired signal but, if close to RFI sources, will also pick up disproportionately more of the local noise. This will reduce the SNR and make the overall signal reading poorer, which is why it is not advisable to use large antennas indoors.


The other advantage of a loop antenna is that it is directional. By rotating the loop about its vertical axis one can maximise the reception strength of one particular signal over the others, once the antenna is aligned with the direction from which the signal is coming (this is termed “peaking” the signal). Similarly, it is possible to reduce the strength of a particular local noise source, since the loop is minimally sensitive to a given signal once it is perpendicular the latter’s direction (also known as “nulling” the signal).

It is further possible to lower the effect of local noise sources by moving the antenna around. Because of the antenna’s design, the effect of radio signals is mostly confined to the loop itself as opposed to its feed line. Most local noise sources have irregular radiation patterns indoors, meaning that it is possible find a spot inside your property where their effects are minimised.

Many compact shortwave loop antennas require an additional tuning unit to be attached to the loop base (much like the preselector described above) but broadband loops do not. Wellbrook ALA1530S+ is one such antenna that is only 1m in diameter, and it was the one I chose for my current apartment. I was rather impressed with its performance, although I found that I need to use a preselector with it as the loop occasionally overloads some of my receivers when used on its own. Below is a demo video comparing using my Tecsun PL680’s built-in antenna to using the radio with the Wellbrook loop.

As you can hear, there is a significant improvement in the signal’s readability when the loop is used.

Experiment with a phaser

Although the loop antenna dramatically reduces the levels of ambient RFI getting into the radio,  I also have one particular local noise source which is way too strong for the loop’s nulling capability. Ethernet Over Powerlines (PLT) transmits data across domestic electrical circuits using wall socket adapters, as an alternative to wireless networking. It uses the same frequencies as shortwave, which turns the circuits into powerful transmitting antennas, causing massive interference. One of my neighbours has PLT adapters installed at his property, which intermittently become active and transmit data. When this happens,  it is not merely noise that is generated, but a very intense data signal that spreads across the entire shortwave spectrum, obliterating everything but the strongest stations underneath. Fortunately, a mature piece of radio technology called antenna phasing is available to deal with this problem.

Fig.3 The principle of antenna phaser operation (adapted from an original illustration in Timewave ANC-4's manual)

Fig.3 The principle of antenna phaser operation (adapted from an original illustration in Timewave ANC-4’s manual)

Signal cancellation using phase difference

A phaser unit has two separate antenna inputs and provides one output to be connected to the radio’s external antenna input. The theory of phase-based signal cancellation goes roughly as follows:

  • The same radio signal will arrive at two different, locally separated antennas at essentially the same time.
  • The phase of the signal received at the first antenna will be different to the phase of the same signal received at the second antenna.
  • This phase difference depends on the direction from which the signal is coming, relative to the two antennas.
  • The phaser unit can shift the phases of all signals received at one antenna by the same variable amount.
  • To get rid of a particular (noise) signal using the phaser unit:
    • the signal’s phase at the first antenna has to be shifted by 180° relative to the signal’s phase at the second antenna (thus producing a “mirror image” of the signal received at the second antenna)
    • its amplitude at the first antenna has to be adjusted so that it is the same as the signal’s amplitude at the second antenna
    • the currents from the two antennas are then combined by the unit, and the signal and its mirror image cancel each other out at the unit’s output, while the other signals are preserved.

Noise sampling antenna considerations

To prevent the possibility of the desired signal being cancelled out together with the noise signal — which can happen if they both come from the same direction relative to the antennas — one can use the set-up illustrated in Figure 3, where one antenna is dedicated to picking up the specific noise signal, while the other is geared towards receiving the desired broadcast. That way, even if the phases of both the noise and the desired signals are offset by the same amount, their relative amplitude differences will not be the same, and thus removing the noise signal will not completely cancel out the desired signal (though it will reduce the latter’s strength to some extent).

It is possible to use any antenna combination for phase-based noise signal cancellation. However, one has to be careful that, in the pursuit of removing a specific noise source, one does not introduce more ambient RFI into the radio system by using a poorly designed noise-sampling antenna. After all, the phaser can only cancel out one signal at a time and will pass through everything else picked up by both antennas. This is particularly relevant in urban settings.

For this reason, I chose my noise sampling antenna to also be a Wellbrook ALA1530S+. The additional advantages of this set-up are:

  • It is possible to move both loops around to minimise the amount of ambient RFI.
  • By utilising the loops’ directionality property, one can rotate the noise sampling loop to maximise the strength of the noise signal relative to the desired signal picked up by the main antenna loop.
Two Wellbrook ALA1530S+ antennas combined through a phaser

Two Wellbrook ALA1530S+ antennas combined through a phaser

And now onto the phaser units themselves.

Phaser units

dxe-upload

DX Engineering NCC-1 (image courtesy of dxengineering.com)

I have experimented at length with two phaser units: the MFJ 1026 (manual) and DX Engineering NCC-1 (manual). Both solve the problem of the PLT noise very well, but the NCC-1 offers amplitude and phase tuning controls that are much more precise, making it a lot easier to identify the right parameter settings. Unfortunately this comes at a price, as the NCC-1 is a lot more expensive than the MFJ unit. As before, a preselector is needed between the phaser and the radio to prevent overloading.

Below is a demo of DX Engineering NCC-1 at work on my neighbour’s PLT noise. I have chosen to use my SDR’s waterfall display to illustrate the nefarious effect of this type of radio interference and to show how well the NCC-1 copes with the challenge.

Cost considerations

Fig.4 Final urban noise mitigation schematic

Fig.4 Final urban noise mitigation schematic

It would be fair to say that my final urban noise mitigation set-up, shown in Figure 4, is quite expensive: the total cost of two Wellbrook antennas ($288.38 each), a DX Engineering phaser ($599.95) and a Global AT2000 preselector ($80) comes to $1257. That seems like an astronomical price to pay for enjoying shortwave radio in the inner city! However, at this point another old saying comes to mind, “your radio is only as good as your antenna”. There are many high-end shortwave receivers that cost at least this much (e.g. AOR AR7030), but on their own they won’t be of any use in such a noisy environment. Meanwhile, technological progress has brought about many much cheaper radios that rival the older benchmark rigs in terms of performance, with Software Defined Radios (SDRs) being a particularly good example. It seems fair, then, to invest these cost savings into what makes shortwave listening possible. You may also find that your RFI situation is not as dire as mine and you only need some of the above equipment to solve your noise problems.

Filter audio with DSP

If you have implemented the above noise reduction steps but would still like a less noisy listening experience, consider using a Digital Signal Processing (DSP) solution. There are a number of different approaches and products available on the market, and I shall be reviewing some of them in my next post. Meanwhile, below are two demo videos of using DSP while listening to shortwave. The first clip shows the BHI Compact In-Line Noise Elimination Module at work together with a vintage shortwave receiver (Lowe HF-150). The second video compares using a Tecsun PL-660 portable radio indoors on its own and using the entire RFI mitigation set-up shown in Figure 4 together with a DSP noise reduction feature available in the SDR# software package, while using it with a FunCube Dongle Pro+ SDR. As a side note, it is worth remembering that while DSP approaches can make your listening experience more pleasant, they can’t recover what has been lost due to interfering signals or inadequate antenna design.

Set up a wireless audio relay from your radio shack

The above RFI mitigation techniques can result in a rather clunky set-up that is not particularly portable, confining the listener to a specific location within their home. One way to get around this is by creating a wireless audio relay from your radio shack to the other parts of your house. I did this by combining the Nikkai AV sender/receiver pair and the TaoTronics BA01 portable Bluetooth transmitter:

Head for the outdoors!

So you have tried all of the above and none of it helps? As a last resort (for some, but personally I prefer it!), you can go outside to your nearest park with your portable radio. After all, if shortwave listening is causing you more frustration than joy it’s hardly worth it. On the other hand, you might be surprised by what you’ll be able to hear with a good receiver in a noise-free zone.

Acknowledgements

Many of the above tricks and techniques were taught to me by my Twitter contacts. I am particularly grateful to @marcabbiss@SWLingDotCom, @K7al_L3afta and@sdrsharp for their advice and assistance over the years.


Thank you–!

What I love about my buddy, London Shortwave, is that he didn’t give up SWLing just because his home is inundated with radio interference–rather, he saw it as a challenge. As you can see, over the years, he has designed a system that effectively defeats radio interference.

I also love the fact that he uses an even more simple approach to defeating RFI: he takes his radio outdoors. A kindred spirit, indeed.

I encourage all SWLing Post readers to bookmark and search London Shortwave’s website. It’s a treasure trove for the urban SWL. We thank him for allow us to post this article in its entirety.

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