Sunday, 19 October 2008

DRM - Digital Radio Mondial (2)

I have finished boxing up the 455/12 kHz mixer (http://www/, fitting connectors etc. and I have been spending a bit of time listening to DRM broadcasts. There are about 10 European medium-wave DRM stations, that become available in the evenings and about 20 or so SW stations available here in London at various times of the day. I am also fortunate that there is a local broadcast station on 25695 kHz just up the road from here at Crystal Palace so I always have a strong station to check the set-up.

The DREAM DRM is quite easy to get it going, but it lacks help files so I had to explore to find out how it works. The key menue is 'View'. from there, go to 'Stations' menu, which will give a list of stations. Make sure you 'Update' this regularly - DRM is still experimental so stations come and go. The list automatically indicates the stations available at the current time. Once you have tuned into the station you want (on my FT-817 it best to tune about 3kHz above the stated frequency).

Next select 'Evaluation' from the View menu and select 'Waterfall ' from the 'Spectrum' submenu. With a bit of luck, you will see a screen like the one below and once all the traffic lights at the top of the screen turn green, you will hear the decoded signal from your computer speakers.

Decoding is very sensitive to getting the audio level right. Unfortunately, DREAM does not have any facility to adjust this so you will need to open your 'Sounds' screen from your computer's Control Panel (or Settings) menu. You may need to access the 'Recording' sliders. To do this, go the the 'Options' menu and select 'Properties' and then the 'Recording' button (intuitive it is not!).

Then adjust the relevant input level until the DRM signal is mostly green and yellow, with a bit of red. Please note, shortwave is subject to long-term fading so you may need to adjust the level from time to time.

Listening to DRM is very different to normal shortwave listening. When DREAM is decoding sucessfully, the signals are very good quality (almost FM as most broadcasts are Mode 'B' which is intended for the better paths). However, when it gets overwelmed by sudden changes in path or bad multi-path propagation the signal does not fade it just drops. Once the signal comes back, DREAM usually regains syncronization quite quickly so the absence of signal is minimized.

I will say more next time about the programmes I have listened to. Meanwhile please leave a comment with your own experiences of DRM.


Tuesday, 7 October 2008

October 2m Activity Contest

This has not been a good year for me in this contest. I enjoy going out portable, but almost every month the weather has not been suitable this year. Tonight was no exception, with lashing with rain and strong winds, so I worked the contest from home again.

Conditions were a bit flat, but I did manage 30+ QSOs and 8 squares. Best DX 194 km into IO82.


Sunday, 5 October 2008

DRM - Digital Radio Mondial

I am not really a Shortwave Listener, but I have been experimenting lately with Digital Radio Mondial ( DRM ). This is a new digital mode designed for short medium and long wave bands so intended to be more resistant to fades and noise. If you tune the broadcast bands you will come across blocks, arounf 10 kHz wide, that sounds like noise - that's DRM.

There are several commercial DRM receivers now on the market - Google will point the way, but I went the home-brew route. I bought a 455 kHz -> 12 kHz mixer from Sat-Service Schneider in Germany. This is a circuit, about the size of a postage stamp, that does what it says on the can. I then opened up my Yaesu FT-817 and picked off the 455 kHz IF from the plug intended for the narrow CW or SSB filter (most receivers will have somwhere that the IF can be found easily). I connected this IF, which would contain the 10 kHz-wide DRM signal before it would be crushed by the narrow filtering in the receiver, and passed it to the 455 kHz input of the SSS mixer.

The output at 12 kHz is then passed to my lap top sound card which is running DREAM software that decodes the DRM signals. (Google Dream +drm +radio). DREAM if free and does a lot more than just decode DRM, but more of this on a later post.

I am currently listening to the German stations RTL from their tranmitter in Luxembourg cool music (ghost from the past for those who remeber 208?) - almost error free. I will post more on this subject later.


Wednesday, 1 October 2008

An hour on 30m

The sun spot minimum just seems to keep on going; will we ever see another sunspot?

There is an up-side to this, my favourate band, 30m, produces reasonable activity and as I had an hour to spare this evening I tuned around it. Nothing spectacular but I did work EA8CAC, UA3MAI and Z30U before the band closed - thanks guys! 'Cards' are waiting for you at

That's one of the great things about amateur radio for me - I can enjoy it even if I only have an hour to spare.