On Mon, Sep 7, 2020 at 8:25 AM <op25@zellners.com> wrote:
>
>
> Quoting iain macdonnell - N6ML <ar@dseven.org>:
>
> > Still need to figure out if I can make op25 park on a fixed center
> > frequency and find the channels with the sampled space, but I need
> > something better than the RPi3 to cover the system that I want to
> > monitor (channels span about 5MHz).
>
> OP25 doesn't work that way , and with out a major rewrite to do that
> you are better to just set a smaller bandwidth/sample rate as the rest
> is wasted processing.

It can work that way. It was not working for me because I had an integer (I guess) for the center frequency, instead of a float(??). I changed it from "773" to "773.0", and now it stays centered there, and finds the channels within the 6MHz sampled.

In the past, I've complained that the first word or two of a transmission often gets missed. One theory was that the tuner (RTL dongle back then) was taking some time to effect retuning, and that a solution that doesn't need to retune may be better. I'm still noticing the start of transmissions get missed occasionally, but maybe less than before. I might have to go back to the RTL to try to get a comparison.

When you said "doesn't work that way", perhaps you meant that it doesn't continue decoding the control channel whilst simultaneously decoding a voice channel? I believe that that's true, although it does monitor control traffic on the voice channel.

I'm not sure if there's any latency involved in "offset retuning".

~iain