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.
[image: center.PNG]
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
