Make sure your radio works correctly first!
Take the top off and remove the PCB you can see here.
Having been to the 2003 SWLFest at Kulsville PA I was exposed to a weekend long demonstration of Digital Radio Mondiale. It seems that to decode these broadcasts one needs to feed a 12KHz IF into your PC's sound card which then gets played out through your speakers. One of the radio's that was being used was a Ten-Tec RX-320. This radio uses a 12KHz IF and so is really easy to modify.
I guess I had better do the disclaimer thing. I will accept no responsibility for anything happening to your radio (or anything else) whilst you undertake this modification. You do it at your own risk. If you do not have the appropriate skills for this mod then seek professional advice.
OK, so I have modified mine and taken a set of pictures to demonstrate how easy it is to do. You are going to attach a wire to pin 1 of the TL082 op amp, connect it to a 0.1uf capacitor and then to the center of a phono socket which you will add. Ground will be via the case/chassis to the circuit board.
A less sophisticated mod (as per Ten-Tec) can be found here.
Make sure your radio works correctly first! |
Take the top off and remove the PCB you can see here. |
 Flip the board over so that the power socket is in the top left corner. The TL082 is the black blob with eight legs. |
 Attach a wire to pin one (top left pin) of the TL082. There are 3 possible soldering opportunities here so you don't have to solder directly to the chip if you don't want to. |
 Remove the CE label from the back panel and install a phono socket in its place. I also labeled the output too. Don't forget to use a center punch to mark where you will drill your hole. Nothing says "cluts" like the scars of a drill bit skidding across your nice painted panels. |
 Re-assemble the radio and connect the new wire to a 0.1uf capacitor and then onto the back of the phono socket. As my phono socket had a plastic isolator around it I had to add a ground wire. I connected it to the ground pin on the voltage regulator. |
When its all back together again turn it on and check that it works as it did before the mod. When you are happy about its functionality you can then connect the phono socket to your sound cards "line in" port. When tuned to a radio station you should hear some very high pitched audio. It'll be almost too high to hear. If this is what your have then all is well. Fire up your DRM software and off you go.
I'm a cheapskate but I relented and bought the software. I have to say that until last night I had been having very little luck with the modification. All of my tests so far have been fairly fruitless. I was struggling to get a satisfactory decode from the software.
Having discussed this at length with the good folks over at the RX320 list on Yahoo I decided to take the sum of the knowledge and give it another go. It seems that the IF output from the 320 is WAY TOO LOUD!! and so needs to be attenuated. This is did with a 10k variable resistor across the IF with the wiper going to the sound card. This allowed the sound card to operate properly so was a good start and showed an improvement in the S:N ratio.
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I then changed the antenna to a lesser one. Until now I was using a dipole antenna from my ham shack which was providing lots of lovely radio signals. Problem was that the AGC in the radio was killing the desired signal so I changed the antenna over to one of my 2 meter ham band antennas. I now had a slightly lesser signal and an improved S:N ratio.
The S:N ratio of a good setup is expected to be about 26db. This will provide you with 100% decode of the data. Typically the 320 would struggle to produce 15db which would produce about 40% decode. This was the combined opinion of all whom had tried it. As you can see from the below picture and log file, it now works!
>>>> DRMSoftwareRadio-MERLIN-00000344 Software Version 1.0.21 Starttime (UTC) 2003-05-07 00:00:06 Frequency 15525 kHz Latitude 40°29'N Longitude 72°27'E
MINUTE SNR SYNC AUDIO TYPE 0000 24 150 1500/10 0 0001 24 150 1500/10 0 0002 24 150 1500/10 0 0003 23 150 1500/10 0 0004 24 150 1500/10 0 0005 25 150 1500/10 0 0006 24 150 1500/10 0 0007 25 150 1500/10 0 0008 24 150 1500/10 0 0009 24 150 1500/10 0 0010 24 150 1500/10 0 0011 24 150 1500/10 0 0012 24 150 1500/10 0 0013 23 150 1468/10 0 0014 16 150 1124/10 0 0015 16 136 931/10 0 0016 15 123 401/10 0 0017 16 150 969/10 0 0018 16 150 948/10 0 0019 16 150 881/10 0 0020 20 150 1147/10 0 0021 24 150 1500/10 0 0022 23 150 1500/10 0 0023 23 150 1500/10 0 0024 24 151 1510/10 0 0025 24 150 1500/10 0 0026 24 150 1500/10 0 0027 24 150 1500/10 0 0028 24 150 1500/10 0 0029 24 150 1500/10 0 0030 24 150 1500/10 0 0031 24 150 1500/10 0 0032 24 65 662/10 0
CRC: 0x932d <<<<
So there you have it. It works. Here's a brief audio file (600K MP3). If you need some help with this, drop me a line.
© & ® Mark A Phillips, G7LTT 1995-2004
This page was last updated Sunday, March 13, 2005 09:21:01 Eastern Standard Time