Brilliant Article on RTL-SDR Dongle Uses

sdr-Mario2Frequent contributor Mario Filippi N2HUN has written a brilliant piece for the latest edition of The Spectrum Monitor entitled RTL-SDR: Your Eye To The Wireless World, February 2016. Here is a brief synopsis:

RTL-SDR Dongle: Your Eye to the Wireless World

By Mario Filippi N2HUN

The RTL-SDR dongle has garnered much popularity over the last several years as an inexpensive and effective broadband receiver for the radio enthusiast. Now Mario shows us how the RTL-SDR can be pressed into serving in other ways: as a rudimentary piece of test equipment to explore those countless wireless devices that power our world and make life convenient. You can use it when restoring vintage radios, doing frequency analysis, antenna analysis and a host of troubleshooting activities you may never have thought of.

I highly recommend buying at least the current issue ($3.00 / PDF Download – what a steal!) or better yet, subscribing for a whole year. Every issue gives far more value than the cost ($2.00/issue at the current subscription rate).

Mario’s article explores things I never would have thought of, and he explains how he uses these inexpensive dongles in place of much more expensive equipment. It is truly amazing what these little wonders can do, and Mario just keeps pushing back the envelope of what is possible.

Thanks Mario for a truly inspiring article – yet again you have given us even more rabbit trails to explore!

Robert Gulley, AK3Q, is the author of this post and a regular contributor to the SWLing Post. Robert also blogs at All Things Radio.

SDRplay shipping the RSP in quantities of 1,000 a month

SDPlay-RSPThis article from Electronics Weekly just popped up in my news feed:

SDRplay of Wakefield, the 18-month-old software defined radio specialist, is now shipping its $149 software defined radio (SDR) receiver in quantities of 1,000 a month

Inspired by the SDR capabilities that even a simple 8-bit TV dongle can perform, SDRplay had the idea of partnering with Mirics to take their 12-bit wideband broadcast chipset and to re-purpose it for the hobbyist market.

At the moment, the hobbyist market for SDR radios tends to be dominated by radio amateurs and ‘short-wave listeners’ and SDRplay’s initial product, the ‘Radio Spectrum Processor’ (RSP) has been well received – winning Ham Radio Science’s RSP ‘Best Bang for the Buck’ rating.

Continue reading at Electronics Weely’s website…

I’m quite proud of the folks at SDRplay as their RSP is truly one of the best receiver values on the market right now.

After (apprehensively) agreeing to review the SDRplay RSP last year, I was simply blown away by this little $149 receiver’s performance. Click here to read the review. Later, I couldn’t bring myself to return the RSP on loan for the review–so I purchased it instead.

I’m glad I bit the bullet!

In fact, last year, at the SWLing Post DXpedition, my buddy, Mark Fahey–who traveled all the way from Australia–forgot to bring the appropriate power adapter for his WinRadio Excalibur, so I let him use mine. I had planned to run the WinRadio Excalibur and Elad FDM-S2 simultaneously on my PC so that I could record spectrum in two different parts of the band at the same time.

Fortunately, I brought the SDRplay RSP, so it took the Excalibur’s place and ran alongside the FDM-S2. It worked amazingly well!

(I should note here that I also believe the FDM-S2 is a great value–at $519 US, it holds its own against receivers that cost upwards of $1,000.)

Shortly after I published my RSP review, I invited SDRplay to become a sponsor of the SWLing Post. I’m happy they accepted. Sponsorship on the SWLing Post is only open to retailers and manufacturers who produce quality goods; those who are well-known in the industry and, often, ones with which I have direct experience. I think SDRplay is a great fit.

So, Kudos to Jon Hudson and his team at SDRplay! I’m very happy to hear how popular the RSP has become.

If you’re an RSP owner, or plan to be soon, make sure you check out the official SDRplay forum and the SDRplay Facebook group: both excellent resources backed by active SDR enthusiasts!

New improved API for the SDRplay RSP

The SDRplay RSP software defined radio

The SDRplay RSP software defined radio

Many thanks to Jon Hudson with SDRplay, who shares the following announcement:

We are pleased to announce release 1.8.0 of the API for the RSP. This is a major upgrade to the API with new features and an improved gain map which should result in improved performance over a key portion of the gain control range. Currently this API is available for Windows only, but versions for Linux and Mac OS and Android will follow shortly.

The API now incorporates automatic post tuner DC offset correction and I/Q compensation. This will almost completely eliminate the DC centre spike that was previously present in zero IF mode and also correct for amplitude and phase errors in the I/Q signal paths that can lead to in-band images when strong signals are present.

There is a new gain map for the RSP which should help improve the receiver noise floor for gain reduction settings in the range of 59-78 dB. To achieve this, the IF gain control range has been increased from 59 to 78 dB. In addition, the user can now turn the LNA on or off at any point within the IF gain control range. This means that the LNA can remain on for gain reduction settings of up to 78 dB, whereas previously the maximum gain reduction that could be attained whilst the LNA was on was only 59 dB. Being able to leave the LNA on will result in improvements in the receiver noise performance for gain reductions in the range of 59 to 78 dB. The upper 19 dB of the IF gain control range have now been disabled. In practice this part of the gain control range was useless as trying to operate within this region always lead to receiver overload even when signals were very weak.

To fully exploit the features of this new API release, we have also issued release 3.5 of the ExtIO plugin. This plugin will work with HDSDR, SDR sharp (releases 1361 or earlier) and Studio 1. Automatic I/Q compensation and DC offset correction will work with later versions of SDR sharp, but we will need to update the native plugin for users of these later versions to be access the new gain map.

Similarly, users of SDR Console will gain the benefit of automatic DC offset compensation and I/Q correction, but will not yet be able to access the new gain map. We hope that a version of SDR console that unlocks this feature will become available in the near future.

Until a new release of SDR-Console is available, you can copy the API into the SDR-Console installation directory…

from C:\Program Files\MiricsSDR\API\x64\mir_sdr_api.dll to C:\Program Files\SDR-RADIO-PRO.com\mir_sdr_api.dll

The API installer has also contains an extra certificate to be more user friendly for Windows XP, Vista and Windows 7 users.

The new API and ExtIO plugin can be downloaded from our website at: www.sdrplay.com/windows.html

Many thanks for sharing this, John!  I’ll update my RSP today.

Click here to read the SWLing Post review of the SDRplay RSP.

Now Online: A New WebSDR in Iran

WebSDR-Iran-Waterfall

SWLing Post contributor, Mehdi, has informed me that his ham radio club (EP2C) has just put a WebSDR online in Iran–perhaps the first in this part of the world. Mehdi notes some of the details about the receiver:

[The WebSDR is] installed and operated by our amateur club: EP2C (www.ep2c.ir)

[Perhaps] the first WebSDR in the Middle East (the nearest one I know of is located at Armenia). We have a dipole antenna and an AVALA SDR receiver (going to be replaced by a SoftRock).

For the moment, it just covers 20 meter band, but we may increase the coverage to 30 and 40 meters too.

The server and antenna are all in EP2C club’s office (Karaj/Iran). Iran’s timezone is GMT+03:30.

Because of our bandwidth limitations, the total number of simultaneous users is limited to 10 (will try to increase it in the future).

Our WebSDR address: http://websdr.ir:34567

Thank you for the announcement, Mehdi! I’ve been listening to the EP2C WebSDR this morning–it’s been working flawlessly.

Please keep up informed as you improve and upgrade the EP2C WebSDR!

Click here to use to the EP2C WebSDR online.

HDTV via an SDRplay RSP

tvpic2

Check this out: a tutorial on decoding ATSC HDTV via the SDRPlay RSP software defined receiver.

(Source: coolsdrstuff.blogspot.com)

One of the main reasons I got the SDRPlay RSP was its wide bandwidth. It can show up to 8 MHz of spectrum at once. I figured it should be able to watch TV. Turns out it can, but it’s only designed to receive DVB-T.

Unfortunately, they only use that in Europe and a few other places. In North America we use ATSC.

In this article I will show how to use it to watch ATSC.

Click here to read the full tutorial…

This is one of the things I love about SDRs: in many ways, their applications are only limited by your imagination.

Click here to read our review of the SDRplay RSP.

Used Microtelecom Perseus $729.95 via Universal Radio

MicrotelecomPerseus-1

I regularly check out the used equipment list at Universal Radio. While prices are not rock-bottom, the seller (Universal) is solid. Universal backs all of their used equipment with a 60 day limited warranty and their product descriptions are accurate. Fullscreen capture 10272015 65822 PM

This Microtelecom Perseus (see ad above) appeared in Universal’s used index a few weeks ago.  I assumed it would be snatched up pretty quickly at $729.99 US. I’ve been tempted to purchase it, but since I have no less than five SDRs in my shack at the moment, it would certainly be in excess to my needs.

Why buy a Perseus?  Even though it’s been on the market for many years, the Perseus has an excellent receiver that is comparable to or better than many of the latest SDR offerings. While I’ve never been a huge fan of the Perseus application/software, it is unique in that it allows you to both share your receiver and control other Perseus receivers online. The included server software is relatively easy to implement as well; no doubt, this is why there are so many Perseus receivers online.

I’ve even heard rumors that Microtelecom may be introducing a new Perseus application before long (I certainly hope this is true).

If you’ve been looking for a used Perseus in good condition, I feel like the $729 price is fair from Universal Radio (new units sell for $999.95).

Occasionally, you can find the Perseus used on eBay as well (click here to search).

At the prompting of Mark Fahey, I’m planning to borrow a friend’s Perseus soon and try some of the online functionality. If I make the receiver available through the Perseus online network, I’ll post an update here on the SWLing Post.

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.