Category Archives: Software Defined Radio

A simple homebrew high pass filter

Many thanks to Jon Hudson, of SDRplay, who posted the image above along with the following note on Facebook:

David, WA7JHZ has designed and assembled this neat 2.6 MHz high-pass filter (HPF) for use with SDRs. He says that this simple input band-pass filter (BPF) might be of interest to anyone suffering from strong AM broadcast stations that are causing overloads…..David suffers from three nearby AM radio broadcast stations that overload the front ends of several of his receivers, including the SDRplay RSP and this is an ideal, low cost solution. He built this circuit from junk parts and commented that Amidon T44-2 iron powder cores would have made a better design, but that he decided to keep costs down with this design.

This design is simple enough for almost anyone to build and could help your receiver’s front end from overloading. Many thanks to David for the design/schematic and to Jon for sharing!

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Check out the new web-based KiwiSDR in New Zealand

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Many thanks to SWLing Post contributor, Andrea Borgnino, who shares a link to a new web SDR in New Zealand: The KiwiSDR installation.

Andrea posted the following on Twitter:

The new KiwiSDR is fantastic !! Best web-receiver ever !!! https://t.co/YiIEUE3CIe @SWLingDotCom @LondonShortwave pic.twitter.com/d3i9UVynt7

— Andrea Borgnino IW0HK (@aborgnino) February 9, 2016

I agree with Andrea: this WebSDR has an amazing display and user interface. It even includes both a spectrum and full-color waterfall.

I’ve enjoyed tuning around the mediumwave band in New Zealand this morning. My Internet connection is terribly slow (and unreliable) but I was still able to view the full display while streaming audio with only a few hiccups. With a moderately robust Internet connection, I believe you’ll be pleased with the KiwiSDR.

Click here to visit the KiwiSDR online.

Many thanks, Andrea, for the tip!

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Brilliant Article on RTL-SDR Dongle Uses

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Frequent 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.

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Chris has developed an easy way to run the RTL-SDR dongle on a Mac

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Many thanks to Chris Smolinski who writes:

I wanted to run SdrDx, and other SDR apps on my Mac with an RTL SDR Dongle. So I wrote this server app, that makes it appear like a networked SDR.

No need to install any RTL libraries, or compile any code.

Just run the app on your Mac, configure it and your SDR app, and you’re all set.

The app is free, and should work with Mac OS X 10.6 through 10.11.

Chris has kindly allowed me to share his full post here on the SWLing Post below–you can read the original at RadioHobbyist.org:

Running an RTL SDR USB Dongle On Your Mac The Easy Way With Cocoa RTL Server

I’ve had a few of the RTL radio tuner dongles for a while. These are USB devices that were originally made for use as TV tuners overseas, but it turns out that you can access the I/Q data stream, and turn them into an SDR (Software Defined Radio). They can be tuned roughly over a range of 25 to 1700 MHz, and sometimes even higher, depending on the tuner IC chip inside the particular dongle.

I previously posted about how to get the RTL dongle working on the Mac here: An SDR for $17 – The R820T USB RTL-SDR DVB-T Dongle and here: An SDR for $17 – The R820T USB RTL-SDR DVB-T Dongle – Part 2. These posts were from 2013, and I did the installation on a Mac running OS X 10.6, using some pre-built libraries.

Fast forward to the present day. I got a new Mac running OS X 10.11 El Capitan, and I wanted to be able to use the RTL dongles with my favorite SDR software on the Mac,SdrDx. Enter Cocoa RTL Server.

Cocoa RTL Server is a stand alone app that interfaces with an RTL dongle. It does not require you to build or install any drivers or libraries. It just works. It’s based off of an open source app called SoftShell, that I heavily extended. Cocoa RTL Server also acts like a networked SDR, following the RF Space protocol. That means it works with SdrDx, as well as any other SDR app on the Mac that supports RF Space SDRs like the netSDR. You can download a copy of the app from the Cocoa RTL Server page. Source code is included, however I am not offering any support for the project or final app.

Here’s a screenshot of the app running:

Getting up and running is easy:

1. Plug in your RTL device
2. Run CocoaRTLServer 2.0
3. Select the device from the popup menu (usually it is already selected)
4. Change the rtl_tcp or tx_tcp port values if needed
5. Click Open
6. Configure your SDR app (set the correct TCP port) and run it

I’ve run it under Mac OS X 10.6, 10.10 and 10.11, It should run under 10.7-10.9 as well.

Using SdrDx, I can tune a large portion of the FM broadcast band, click to view full size:

In this case I am tuned to 97.9 MHz. To the left of the signal meter, you can see it has decoded the station ID from the RDS data. Yes, SdrDx decodes RDS.

If you look at the lower right corner, you see the scope display of the demodulated FM audio. There are markers for the portions of interest:
You can see the main audio above the green marker to the left.
The stereo pilot at 19 kHz (red marker).
The stereo subcarrier (aquamarine)
The RDS data (orange)
The 67 kHz SCA subcarrier (purple)
The 92 kHz SCA subcarrier (yellow)

Cocoa RTL Server also includes a server that emulates rtl_tcp, so it works withCocoa1090 which decodes aircraft transponders that transmit on 1090 MHz. It should also work with any other app that gets data from rtl_tcp. Here’s a screenshot of Cocoa1090 running:

Thanks so much for developing this app, Chris!

I think I might go ahead and pull the trigger on an RTL-SDR as it would be great to run one on my Mac. I think your app will make the process much easier.

Readers: make sure you check out Chris’ blog RadioHobbyist.org.

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

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SDPlay-RSP This 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!

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New improved API for the SDRplay RSP

How to use the SDRPlay RSP as a panadapter

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SDPlay-RSP

In this post, I will show you how to use an SDR as a panadapter for a commercial communications receiver. I’m using an Icom R72 and a SDRPlay RSP, but you can do it with nearly all receivers and SDRs.

The Icom R72 is a double conversion HF (0-30 MHz) communications receiver.

A panadapter lets you see the spectrum of your receiver (it gives you a broader, higher-level picture of what’s around your tuned frequency). After using it, you’ll wonder how you’ve been using your receiver without a spectrum display! 🙂

Almost all the radios we use are of superhetrodyne type. To connect a SDR to the radio, you should first find its 1st IF mixer output (if it has more than one Intermediate Frequency stage).

To find it, the best way is to consult the service manual. The first IF of Icom R72 is 70.4500 MHz, so we can use RTL-SDR dongles too.

Here’s a part of R72’s schematics, extracted from its service manual:

IC-R72-Schematic-Mehdi-Asgari

Look at the R82 resistor; it’s located at the output of first IF stage, so I soldered a connector to its pins (its other pin is connected to the ground)

Between the R82 resistor and the output, we’ve added a series 470-ohm resistor (to prevent loading the IF stage)

Click to enlarge.

The other side of this connector is connected to the antenna input of my SDRPlay RSP.

Now I can view my spectrum on a PC.

Here’s a screenshot of CubicSDR on Mac OS X (you can use other apps like HDSDR, SDR Console, etc.):

CubicSDR-Screenshot-Mehdi

Although this post was about the SDRPlay RSP and Icom R72, this procedure can be done for almost any combination of receivers and SDRs provided that your SDR covers the frequency of first IF stage.

Also, don’t forget that you should tune the SDR to the frequency of IF–in this case: 70.4500 MHz.

Mehdi Asgari, the author of this post, is a regular contributor to the SWLing Post. Mehdi lives in Tehran and is an active member of the EP2C amateur radio club.

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