I’ve got an old Alinco DR-605T I’ve been putting into service for local ARES (Winlink/VARA FM). These rigs don’t have serial RTS PTT and take audio from the headphone jack.
I’ve noticed that these old radios pick up a lot of RF noise via that phone jack—reasonably sure it’s not from the DigiRig nor from the DIY cable. In my case, it manifests as RF noise and is visible on the S-meter bars. I suspect it is RF in the GoBox where the radio and mini-PC live in close proximity. The noise wreaks havoc with the SNR.
I’m making this post not as a trouble report on DigiRig—and I have this with both a DR Mobile and Lite—but as a suggestion for others that have noisy audio coming out of their radios and into the DigiRig of choice.
I seem to have “tamed the beast” by adding an RC filter between the radio audio jack and the DR cable. Since the AFSK data can’t shift more than 5kHz on V/UHF FM (and 2.8k on HF SSB), a filter with -3dB cutoff at around 5kHz should do the trick.
I chose an RC filter with R=1720 Ohms & C=1909 pF. R is two 3.3 K 2W resistors paralleled (chose 2 that measured & gave me the desired R for the -3dB) and a 1900 silver mica cap (measured at 1909pF). Per the DigiKey RC calculator, this gives me a -3dB cutoff of 4847 Hz.
This attenuates the signal just a little but really cuts off the higher frequency noise. Since I have the audio cranked way down as it is, this is no problem (just crank it up a smidgen) and really seems to improve the audio presented to the DigiRig.
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YRMV