Ten-Tec RX-320 DRM mods

Convert your RX-320 to receive DRM broadcasts!

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.

rx320-start.jpg (17036 bytes)
Make sure your radio works correctly first!
rx320-topoff.jpg (35912 bytes)
Take the top off and remove the PCB you can see here.
rx320-board.jpg (26032 bytes)
Flip the board over so that the power socket is in the top left corner. The TL082 is the black blob with eight legs.
rx320-wire.jpg (21291 bytes)
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.
rx320-back.jpg (16651 bytes)
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.
rx320-assembled.jpg (40264 bytes)
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.

rx320_mod.jpg (16421 bytes) rx320d_mod.jpg (15326 bytes)

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!

20030506-RX320-RNW.jpg (108788 bytes)

 

>>>>
DRMSoftwareRadio-MERLIN-00000344
Software Version 1.0.21
Starttime (UTC)  2003-05-07 00:00:06
Frequency        15525 kHz
Latitude         4029'N
Longitude        7227'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