Software Defined Radio (SDR)

Military Symbol: Radio Station Welcome to Software Defined Radio.

On this page you will find my review and experience with software defined radios.

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For several years now, I have been wanting to experiment with Software Defined Radio (SDR). SDRs have been in development and in service since the 1980s in military communication applications. One could go as far as to argue that the Rockwell Collins HF-2050 receiver, produced for the Canadian Military, was one of the first receivers in this category as it was the first receiver to employ digital signal processing (DSP). In the early 1990's I had the opportunity to work with a Watkins-Johnson HF-1000. The receiver was somewhat of a disappointment. The HF-1000s performance and features were good but less then a month into service I found myself having to put the unit on the bench and realign the internal frequency standard (TCXO). Once the TCXO was realigned the receiver was back on frequency.


Until recently, most commercial and hobby SDRs worthy of providing solid performance coupled with flexibility have been reasonably expensive. A little over a year ago, a long time friend of mine told me that he had purchased an SDRplay RSP2 as a travel companion receiver. After much procrastination, I decided that it was finally time to jump in and experiment with this new technology. I was sceptical of the performance an SDR would deliver. I live less than 10 km from a major downtown metropolitan area. Historically, any general/average quality broadband receiver that I have owned have all suffered from intermod and IF front-end overload. In August of 2018 I visited my local Amateur Radio shop and invested in my first SDR --- an SDRplay RSPduo.

Having served alongside high-grade commercial and military radios for over 30 years, thus far, the only word that expresses my satisfaction with the SDRplay SDR is WOW! This "little black box" is amazing. For people who know me well, at one time, I used to maintain a fairly impressive collection of high-end commercial and military grade receivers and transceiver. My collection used to span a wide range --- Eddystone, Harris, Icom, Racal, Rockwell Collins, Rohde & Schwarz and Watkins-Johnson just to name a few. Over the past few years I have been pruning my collection down some what to something more reasonable --- from 4+ racks of equipment down to a little over 2 racks and a few shelves --- keeping only a few prize units in active service.

Let the games begin. I am primarily a VLF/LF/HF band user. For my first test, I put my new RSPduo head-to-head with my Harris RF-590 and Rockwell Collins HF-2050. Well, I have to say, the RSPduo is a pretty good contender against these $15,000.00+ receivers. So far, I am impressed.

For my second test, I decided to put the RSPduo up against my ICOM IC-R8500 in the LOS SATCOM band. Thus far, other than my LST-5 and AN/URC-111, the only other receiver that has been able to intercept the Brazilian pirates on LOS SATCOM has been the ICOM. Now I am really impressed. The RSPduo is intercepting LOS SATCOM.

Hummm, so, what about data you say? With the help of VB-Audio's VB-Cable, routing the audio from the SDRuno's application to a software decoder was a breeze. Test number 3 --- I tuned the RSPduo over to an HFDL frequency and within seconds I was decoding aircraft and ground transmissions.
SDRuno - LOS SATCOM pirates
   Brazilian radio pirates on 255.550 MHz

Let's find something a little more challenging. I tuned over to time and frequency station CHU and after a little over 60 seconds I was decoding valid time code. This all software configuration, SDR + decoders, operated from a single desktop is far more convenient then my traditional analog cables from receiver balanced audio outputs to either my external modems, demodulators or computer sound card. Another win-win for the SDR.

   Above: HFDL data decoding
   Top right: Time and frequency station CHU at 3330 kHz
   Bellow right: CHU time code decoding

CHU time code decoding
Last week, my old time friend and I were having dinner along with our traditional radio geek talk. The topic of ADS-B (1090) came up in the conversation. 1090 I say? I am not familiar with this. Being a basement band dweller, other than for the VHF aircraft band and LOS SATCOM, I do not venture much above 20 MHz.
ADS-B dipole antenna
   ADS-B vertical dipole
After a few hours of educating myself on the topic I built a 1090 MHz vertical dipole antenna. Test number 4 --- ADS-B. Once again, the RSPduo was no disappointment. No dongles, amplifiers or special filters were used and within minutes I was decoding extended squitter data.
Virtual Radar
Virtual Radar pulling ADS-B squitter data dump1090
Reading some of the various on-line presentations on the RSP series of receivers, it appears that there are many more hours of enjoyment in store for me as I start to explore new capabilities such as NOAA weather satellite data just to name one. I have a feeling that my RSPduo might even replace my Mason A-3B TSCM receiver. It is more than capable of the task at hand and a whole lot lighter to carry around.
For those who are not certain if and SDR is in the horizon for them or maybe would like to experiment with one first from the comfort of their home, I highly encourage you try one of the many public access WebSDRs available on-line. One of my favourites is the one located at the University of Twente, Enschede, NL as it allows me access to VLF, LF and SWL content not available in North America. Hello BBC at 198 kHz, D Europe at 183 kHz or Radio Mi Amigo International at 6085 kHz.
European LF Spectrum
In my opinion, for the price vs. value, an SDRplay RSP receiver is a great investment. Sensitivity is very good and the receiver's front-end is holding up remarkably well to overload and intermod. Because of my geographical location I do suffer somewhat from overload, predominantly in the VHF low band. Adjusting the receiver's built-in RF attenuator easily compensates with this issue. Otherwise, the only other anomaly that I have observed is with the AM discriminator when the receiver is in cold start. The AM audio sounds like notched out bad off-frequency SSB. Once you start tuning around, changing modes and the LO syncs up the problem disappears. I have only noticed this in AM mode. This may be attributed to a software glitch. Time will tell. For now my RSPduo is in service and comfortably tucked away in my communication rack and will be accompanying me on future road trips.

Perhaps some day I will have the opportunity to review an RFSpace NetSDR or a PERSEUS receiver. I find the NetSDR very appealing to my radio monitoring envy.

Test Environment:
Receiver: SDRplay model RSPduo
HF antenna: Barker & Williamson model BWD-90
LOS SATCOM antenna: Dorne & Margolin model DMC-120
ADS-B antenna: home built 136 mm vertical dipole (RG-58 coax)

About the author.

Richard Lacroix has been a radio hobbyist since the mid 1970s and has been professionally active in both the commercial and military communication field since the mid 1980s.

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Information & Security Disclaimer

First published: September 08, 2018
Revised: September 09, 2018
(C) 2018-2024, Richard Lacroix. All rights reserved.

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