Software Defined Radio (SDR) - First Steps

I have often seen adverts in the amateur radio press for Software Defined Radios (SDR) and wondered why they are so expensive. During a discussion at my radio club (Cray Valley - www.cvrs.org), I learned that a TV/Radio Dongle receiver can provide the hardware for SDR. I found a suitable dongle (RTL2832 plus either R820 or E4000 chip set) on Ebay; ten UK Pounds from Hong Kong so, being the last of the big spenders, I went ahead and ordered. While I was waiting for it to arrive, I downloaded a copy of SDR Sharp  (SDR#) and the installation instructions (http://www.sdrsharp.com ).
 

There are some hardware things that I needed to do while waiting for the dongle. The dongle has a tiny MCX antenna plug. Fortunately Maplin sells an adaptor cable to standard TV socket (part N59LN) and I had already made a TV-BNC cable for another project, so this was not a problem. These dongles are very vulnerable to high levels of RF, so if you transmit while receiving on the dongle it will fry. The solution is to solder a couple of reversed diodes into the adaptor cable to limit the maximum input voltage.

The dongle arrived. The package also contained a remote control (only useful if you want to use the dongle for its intended purpose, but being radio amateurs we don’t do that do we?), a whip antenna (which works surprisingly well) and a software disk. Do not install this software as this will conflict with SDR#. The only tricky bit was changing the dongle driver from the Windows default to RTL 2832. To do this, you need a piece of software called Zadig (link on the SDR# site) and I also had to temporarily disable Heuristic protection in Norton which took violent exception to what I was trying to do.

All set, and Norton back to full protection, I plugged in the dongle and fired up the software. Operation was quite intuitive, but I started with the FM broadcast band – all was well and all the expected stations showed up on the display any gave me some strong, predictable signals to set up and learn how to use the software.

 

 

The dongle, with the E4000 tuner, covers from about 24MHz up to 1.7GHz, so it is a broadband device covering all the amateur bands from 12m up to 23cm. That’s the good news; the bad news is that there is no front-end filtering. Also these dongles mix the RF signal down to a few tens of kilohertz, to input to computer sound cards, so spurious signals are a real problem, particularly on the lower bands. For example I get a strong ‘Classic FM’ signal in the middle of the 10m band. It is possible to manage these phantom signals by carefully choosing the ‘Centre’ frequency and adjusting the RF gain, which can be accessed through the ‘Configuration’ menu, but my next move will be to build some filters to clean up the input signals.

I have also experimented with receiving  some digital modes using this SDR receiver. It is possible to patch the microphone socket to the speaker socket on most PCs so the digital modes can be decoded with standard software. There are a couple of drawbacks: you can’t hear the audio signal and the signal gets converted from digital to audio then back to digital again. There is a better solution – a piece of software called Virtual Audio Cable (  http://software.muzychenko.net/eng/vac.htm ), which does what the name suggests, but without the Digital/Audio conversions. With VAC, it is possible to ‘split’ the system so the audio output can be heard, recorded or shared with other programmes. I have successfully decoded RTTY, PSK-31 etc.

My Dongle SDR has several advantages: it is very small and everything is controlled from the keyboard so easy to configure. For example, filter bandwidth can be adjusted very precisely and easily.  The waterfall display, which can be adjusted, allows large segments of a band to be viewed at once and you can see when stations come and go then click on the ones you want to listen to. Combining the SDR with the VAC software provides a very flexible setup. For example, I can operate digi-modes while listening to my favourite music on the same computer. 

This SDR radio will never be as good as a full communications receiver, but it was definitely worth a tenner and I hope its performance will be even better with some front-end filtering. It has opened lots of opportunities for experimentation that were not available to me before and after this initial experiment, I may be tempted to invest in an SDR transceiver, but that is for another day.

10m (28 MHz) Activity

At long last the solar cycle has improved and the 10m (28 MHz) band has been 'open' during daylight hours recently.

Last weekend was the CQ World Wide (www.cqww.com) international amateur radio contest. This is a major event and as the weather was so bad over the weekend I was able to spend a bit of time operating. I decided to run just low power (5 Watts QRP, this is about the same power as a Christmas tree light!) and just one band - 10m. I was using my Yaesu FT-817 with a home-made vertical dipole in my loft. Conditons were quite good and I managed to work 116 other stations from the Middle East to USA East Coast.

Also on the 10m band, today I was able to pick up an amateur radio repeater, N2ACF/R, ( http://www.rra.net/ ) which is located in Rockland County north of New York City. This was carrying traffic for the amateur radio emergency net in preparation for the arrival of Tropical Storm Sandy, that is widely predicted to cause major damage in the New York area. I wish everyone in the path of the storm well and, while I hope the amateur radio support is not needed, I am pleased to see that the capability is available if needed.

Dave

6 Metre SMIRK Contest WInner

I am not a major amateur radio contester, but if I hear a contest in progress I will sometimes join in to give away a few points and to keep up my skill level. Occasionally, I will even submit a log.

So it was last June that I heard stations calling CQ Contest on 6m. A quick check of the contest database, which I have on my iPhone, gave me the rules for this SMIRK contest (http://www.smirk.org.) Conditions were good so I worked a few stations, sent my log off to the organisers and thought no more about it.

To my surprise, this week I received an envelope postmarked Pennsylvania and inside was a certificate confirming I had won first place in England! I checked the web site and sure enough, there I was. Unfortunately, I was the only station from England to submit a log which rather took the gloss off my achievement, but this is the only time I have ever come anywhere near the top of any contest so I don’t feel too bad about the lack of competition.

My 6m station is very modest – FT-817 running just 5 Watts and a home-made non-rotatable dipole, fabricated from some old  22mm copper pipe in the loft. But even with this, I can work all over Europe and occasionally beyond when there is a good E-opening.

So, it is worth entering contests even with a very modest score, and thanks to the SMIRK 6m club for running this event.

Dave M0BGR

Operating 2o12L and Mo0BGR

I got up early this morning to operate 2o12L (http://www.2o12L.com. Good session on 20m CW (Morse). Band condiitons were not great but lots of European stations and a few Asiatic Russians worked. I had hoped for some Far East stations, but conditions were not up to this. Unfortunately there were still lots calling when I had to close down to go to work (http://www.howardcommunications.ltd.uk) :-(



2o12L Antennas (some of them!).



Last night, I worked CW (Morse) on 30m from my own station Mo0BGR. Someone kindly 'spotted' me on the DX cluster so I got a nice run of stations. Nothing like a 2o12L pile up, as my station is slightly more modest, but it still kept me busy for a while.

Olympic Special Event Stations

I activated my own special event call, Mo0BGR with a short session on CW (Morse) last night. Conditions were not great, but the first station I worked was UX5MZ - thanks Igor.

Meanwhile over in Eltham, SE London not far from the Olympic venues, the Cray Valley special event 2o12L is going great guns, having worked over 5,000 contacts and 100 countries since Wednesday. For more details go to www.2o12l.com where you can find a list their working frequencies. 

If you are in London, before 9th September, then try to go along and visit 2o12L, how to get there is also on the web site and it is a really impressive station.

FM Switch Off - OFCOM Response

In August ast year I published a post on the governments plans to switch off FM radio in UK(http://m0bgr.blogspot.co.uk/2011/08/dab-radio-switching-off-fm-and-am.html ). At that time OFCOM was holding a 'consultation' and they have now responded to its findings. Their report is at http://stakeholders.ofcom.org.uk/binaries/consultations/dab-coverage-planning/statement/statement.pdf .

As predicted, OFCOM have swept aside all objections to the plan and asserted their previously held position that DAB is very wonderful so we don't need FM (subtext, the government have told us to sell the spectrum, just like they are now selling part of 143MHz - 156MHz band).

I have nothing against DAB radio, but I do not see it as a replacement for FM. It is technically inferior in many ways, particularly its coverage charateristics. DAB is based on obsolete technology and UK will have to adopt DAB+ or DRM at some point. DAB and FM do not use the same spectrum so, unlike the TV digital switch over, there is no need to close FM to allow expansion of DAB. Reading the consultation responses, the radio industry seems distinctly like warm about  switching to DAB.

If you use FM radio in UK, please let OFCOM know what you think.

Roberts DAB Radios

We have recently bought two new DAB radios.

The first was a Roberts Ecologic 1. We bought this for the house we own in Wells-next-the Sea in Norfolk.

This is an area where we are told that DAB radio signals are not available (http://www.ukdigitalradio.com/images/coverage-map.gif) but with the Ecologic 1 we are able to get good signals from two multiplexers and one more when the radio is upstairs. By comparison, my older Sony XDR-S55 radio does not get anything there on DAB.

The Ecologic 1 is a small DAB/FM radio with ½ Watt audio output. This is fine for normal listening, but is not really powerful enough for use in the kitchen when there is lots of background noise. Otherwise, it is a very good radio with excellent mono (stereo with headphones) sound quality. It is well designed and very easy to use. The only thing I don’t like is that it has push-button volume control, but this is a matter of personal preference.

The Roberts Unologic DAB / FM radio is a bit larger but with 1 Watt audio output it is better for use in normal areas. This radio also has excellent sensitivity, but I have not yet done a side-by-side comparison. The Unologic has an analogue volume control, which I like. The controls are large and easy to use so it would be suitable for old or infirm people.

DAB radios eat batteries, but at long last, a DAB radio designer has realised that we don’t want to run our radios from mains power or change the batteries every 10 hours or so. The Roberts Ecologic 1 and Unologic both have built-in battery chargers so can be run on AA alkali batteries (if you are very rich) or rechargeable batteries. The only criticism I have of the design is that it is not possible to charge the batteries while listening.

All round, these are both excellent radios and well worth the recommended price of £60. It is particularly suitable if you want to use it in a poor signal area.

MQ0BGR QRT. MO0BGR Coming up!

My special event call sign, MQ0BGR to celebrate the Queen Elizabeth II’s Golden Jubilee, has now closed down (QRT).The licence expired at midnight at the end of 10^th June so it will not be back on the air again.

Thanks to all who worked me, but the level of interest was a little disappointing. I worked only 65 stations in 18 countries. Some of this was down to me because I was running low power and was away from London for part of the time. Propagation was quite average during the event. Interest was good at the start, but towards the end I had several sessions calling CQ with no response. My belief is that the duration was too long so MQ was no longer ‘special’. I think that for future events, two weekends and the week in between would be enough time for 'special' call signs.

All QSOs have now been uploaded to eQSL, but if I missed any or misread your call sign do let me know. So far, 21 (30%) stations have sent me eQSLs – thanks! I will send paper cards via the bureau only for those I receive or that are requested.

Turning to the future, I have a licence for the Olympics special call sign, MO0BGR (Mike Oscar Zero….) from 21 July to 7th September. This coincides with the operation of my club’s (Cray Valley Radio Society) special station 2O12L (2 Oscar 12 Lima), which I hope to operate. So given the lack of interest in MQ0BGR, I am inclined to use my ‘radio time’ at 2O12L and not to do much with MO0BGR, but we shall see.

Thanks again for those who worked MQ0BGR and have sent QSLs.

73

Dave

MQ0BGR QSL Cards

The prefered QSL route for MQ0BGR is via eQSL, so please use that if possible. I have tried to activate the log book on qrz.com, but as their software does not currently support callsign variants I can't use this route. I am sorry, I do not use LoTW.

If you really want a paper QSL card then do let me know as these will only be sent on request. Don't forget, you can either print cards yourself from eQSL or order paper cards from them which will be sent to you by post.

QSL cards for any data mode QSOs will be sent via eQSL immediately and automatically at the end of the QSO. I am a bit behind with the 'cards' for other modes, but will catch up soon.

MQ0BGR ends on 10th June, so I hope to work you before then.

73

Dave 

I was on the air again last night as MQ0BGR on 30m CW. Nice run of European stations, not a pile up but kept me busy for a while. Then propagation took a turn for the worse, with signals weakening, noise increasing and QSB (fading) making life difficult. Apologies to those stations I could not work, particularly I1ULJ who vanished into the QSB. I did copy enough to put you in the log, but I hate not being able to complete a contact.

After closing on CW I left my station running on 30m WSPR (http://wsprnet.org/ ) - propagation overnight was very poor indeed, with very few stations heard.  I checked to solar web sites this morning and I see there was a major disturbance on the sun yesterday from sunspot 1476, which may have upset propagation last night.

MQ0BGR is Now Active

My Special Event call sign, MQ0BGR is now active. I was on the air last night  straight after the new call sign came into effect. My first QSO was with OG2O (thanks Eikka) on CW. The most interesting QSO was with EA5HWP on 20m CW this morning. Luis was running only 700 mW QRP and we managed to exchange a lot more than just RST which makes QSOs like this very satisfying, so thanks Luis.

Interest in the special call sign was not as high as I expected and I had to call 'CQ' quite a lot to get a response.  I was only spotted once, by RM8W (thanks Andrey).

The solar conditions today remained grim, with an SFI only 107, so I worked mostly 30m, with occasional trips to 40m and 20m on CW or PSK. If conditions improve, then I will try the higher bands and might even be tempted to use SSB.

All QSOs to the end of today (5 May) are now on eQSL.

And, if you were wondering, here is a picture of my shack!

73

Dave MQ0BGR

Mo0BGR - Special Callsign for Olympics

Special call signs seem to be a lot like London buses (http://www.tfl.gov.uk/modalpages/2605.aspx)  - none for ages, then two come along at once.

I now have my licence variation for MO0BGR (Mike Oscar Zero Bravo Golf Romeo), which is valid from 21 July to  9 September 2012. This comes straight after MQ0BGR, from 5 May to 10 June 2012.

I understand that many stations will want to work these special event call signs but I am not sure if I will get on the air much with MO0BGR. The reasons are that I will also be operating the Cray Valley Radio Society special event station, 2O12L ( 2 Oscar 12 Lima http://www.2o12l.com/ ), this is peak holiday season so I may be away and it comes straight after MQ0BGR. If I do get on the air with MO0BGR, this will mostly be on PSK-31 and CW (Morse) QRP.

For CW (Morse), I operate at 20 words per minute , so don't call faster than this. If your CW is not yet up to 20 wpm, just send "QRS" and I will be very happy to slow down to your speed.

Again, most QSLs for MO0BGR will be via eQSL; paper cards will only be sent on request.

Dave M0BGR
http://www.howardcommunications.ltd.uk

MQ0BGR Special Callsign

I now have approval from OFCOM to use a special call sign MQ0BGR from 5 May to 10 June. This 'Q' addition is to mark the Queen's Jubilee celebrations this year.

I expect to be active mostly on CW and PSK-31. QSL will only be electronic, via eQSL Last time we had a special call, MR0BGR,  I went to a lot of time and trouble to send out paper QSL cards, and to date I have not received a single paper card back! eQSL, on the other hand, has a return rate of nearly 70%.

If you REALLY must have a paper card, then let me know and I will send one to you when I get your card.

73

Dave