RX-321 DRM Modification 

This radio recently appeared on Ebay. This page documents the modifications required for DRM reception.

I followed the Ten-Tec modification as per their service bulletin. A copy of which can be found here. Click on the pictures to enlarge them.

I will not accept any responsibility for failed conversions. Modify at your own risk. No warranty Given or implied. Seek Doctors advice before commencing a diet. Do not take with alcohol.

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It's really easy to do. On a clean working area (not like mine!) orient the radio so that the sockets are facing you. Remove the 4 screws on the sides and then remove the 4 screws on the top four corners.
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Remove the top cover. This picture shows the inside of the radio. This is the RF part of the radio. Had we removed the bottom cover we would have seen the DSP part. Note the black cable on the right labeled "4". This carries the 12KHz IF from the radio to the DSP.

 

 

 

Take a look on the rear panel (the one with the sockets) and find a place to drill a 1/4" hole. Into this hole you should install a 1/8" jack socket. Cut the black cable into 2 at a convenient point. You will discover that it is actually a coaxial cable. Strip both part of the cut cable so as to expose both the inner and outer of both pieces. Join the inner and outer part to their respective counterpart on the other wire leaving some room to add the Voltage Divider we shall make in the next step.
 

 

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This is a Voltage Divider. It is made of 2 1K2 (brown/red/red) resistors. Fashion yours like the above picture. This device will reduce the voltage of the 12KHz IF so that it will not overload your PC and thus cause your DRM data decode to fail. When installed the voltage on the twisted bit that will connect to your computer should be about 1 volt peak to peak.
Sorry, no picture.

Find a spot on the circuit board that is entirely green. Take an Exacto knife and scratch away a small area of the green solder mask until you can see about 1/8" square of bright copper. Put a blob of solder onto the copper patch. Make sure to give the copper plenty of heat as the thermal load is quite large and the solder may not take.

Solder one end of your Voltage Divider to the copper patch.

 

 

Now attach the inner of the coax cable to the horizontal part of the Voltage Divider. The twisted bit of the divider gets installed onto the "tip" of the 1/8" socket. Just to make sure that your 1/8" plug gets properly grounded, connect the "ring" of the socket to either the shield of the coax or scratch off another spot on the board and connect it there. finished-small.jpg (87452 bytes)
Check your work for shorts and bad solder joints and then test it on your computer. When you connect the 12KHz IF to your sound card you should hear a high pitch whistle. If you have spectrum analyzer software you should see a 12KHz(ish) signal there. There's an analyzer in the latest copy of DReaM. Just flip it to AM mode. If you are tuned to your local AM station you should see a large spike. Click on this and you should hear the AM station coming out of your computer. Put the top back on and install all the screws. You're done!! Told you it was easy!!

 

& Mark A Phillips, G7LTT 1995-2005
This page was last updated Sunday March 13, 2005 09:35 Eastern Standard Time