Friday evening I had time to work on the ... / 2014-08-16

2014-08-16 Friday evening I had time to work on the ...
Friday evening I had time to work on the 'digimode' interface for the FT-857 radio. I set up a breadboard with the audio transformers and started making cables from the transformers to the USB audio interface. Then I added the cable to the radio on the other side. All of the earlier mentioned interfaces had resistors to regulate the signal level so I started with 12K resistors between the radio and the transformer in the radio to computer audio path. This gave me a weak signal when recording the result with audacity on the computer so I switched to a 6k8 resistor which improved audio but it still wasn't great. So the resistor was replaced by a simple wire which gave me good audio when recording from the PA00NEWS transmission on the PI3UTR repeater. I did notice some low hum while recording, but I realized that was just the CTCSS tone on the repeater output. Normally this tone is filtered out when hearing the audio through the speaker of a radio.
Testing radio data interface, by Koos van den Hout on flickr
Testing radio data interface, The data interface for the new radio on breadboard for testing
Testing radio data interface with USB audio interface
Testing radio data interface with USB audio interface, The data interface for the new radio linked to the USB audio interface

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