[op25-dev] HackRF options ? More than this needed like the Airspys???

iain macdonnell - N6ML ar at dseven.org
Mon Sep 7 17:02:11 UTC 2020

On Mon, Sep 7, 2020 at 8:25 AM <op25 at zellners.com> wrote:
> Quoting iain macdonnell - N6ML <ar at 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".

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