[NLRS] Summary: 2m IF rig quest

[Doug Reed]

If you decide to go the sound card route, the Signalink USB is certainly a
good option and they do turn up at hamfests often enough. These days, the
DigiRig and DigiRig Lite seem to be very popular but it hits $100 quite
rapidly if you buy their cables. The DigiRig includes CAT control but your
TR-751 does not? You could consider it to be "future proofing" but the
DigiRig must be purchased (configured?) for CAT to match the mfgr of your
radio.

Most of the low cost sound interfaces these days are based on the
CM108/CM119 sound chip. You can use any cheap audio dongle and run audio to
the radio if you have a serial port available for PTT. There are plenty of
audio interface designs that generate VOX-based PTT from the audio input.
The WB8LMF web site has a few designs. The cheapest option is a simple
"Easy Digi" transformer interface between your laptop and the radio. I have
plenty of 600:600 transformers if you want some. Just be certain the
transformers are terminated near 600 ohms or the frequency response will be
poor.

Another product I found recently is the AIOC board. For $20 it is a USB
audio and serial interface for sound card modes. It is perhaps the size of
two postage stamps. You could mount it inside the TR-751 and just bring out
the USB cable. <
https://na6d.com/products/aioc-ham-radio-all-in-one-cable-unsoldered> There
are links on the web page and a number of videos on YouTube that you can
review. It is an open-source product and many people are making them.

You will have to decide if you want to incorporate transformer isolation or
not. Back when PSK31 sound interfaces were new, it was considered mandatory
to isolate the computer and radio to prevent transmitted hum. The Signalink
USB has isolation built-in. Many modern sound interfaces like the DigiRig
and AIOC do not have isolation. Those mfgrs suggest adding an inline USB
Isolator board if you have common-mode hum on your signal.

73, Doug Reed, N0NAS.
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