Icom R1 discriminator tap

Let's be fair: this little receiver has never been a great performer and size was its biggest asset on the market.
Most handsets are probably now collecting dust somewhere, as prices on eBay can be as low as 30/40 Euro.

Mine found a new live as datafeed for the processing of trunk radio control channels, but other users may have interest in ACARS or pagers decoding. Discriminator tapping is necessary to avoid NFM filters cutting out part of the signal, making it harder or impossible to decode.

Please don't follow these instructions if you're not confident with what you're doing and the soldering iron. At this stage there should be no more warranty to void, but of course you could well damage your radio and be on your own with that. Of course I can take no responsability for that and chances are that repair shops may not accept to work on "hacked" devices.

Documentation available on the net suggests tapping pin 11 of integrated circuit TK-10487 on "DET-A".
However, when you open the radio it becomes clear how you won't be able to solder directly on the IC, as it's located between two of those tight vertical boards.

More in detail, we're talking of the third from the right, pin 11 being on the main board's side.

Luckily diagrams show how the NFM discriminator output is fed out from the DET-A board to reach DET-B.

Signal is available on one of the pins connecting DET-A to the main board. Those can be easily reached from below the main board, which can be unmounted removing the 4 screws indicated by red markings in the image above and desoldering the lead from main board to antenna connector.

Once the innards have been removed, looking at the bottom with battery pack towards you, DETOUT is located on the third row of pins, third from the top. Solder one wire there and another on one of the many available ground points. With a trunked radio control channel tuned I measured about 0,5V between the two. I mostly get 100% signal quality reading on "Trunker" like programs, while a feed from the earphone plug gives "no-signal" or 0%.
I used part of a connector scavanged from a dead PC to make a socket on the right hand side of the radio. You can definitely do a better job.

Remember to solder back the antenna lead when reassembling your receiver.

Spectrogram of signal taken from earphone plug: the 0-200 Hz range is filtered out.
Spectrogram of signal taken from discriminator tap.

Last update: 8-Jul-06