[op25-dev] scope

Brett Friermood brett.friermood@gmail.com [op25-dev] op25-dev at yahoogroups.com
Sat Jun 25 20:09:44 UTC 2016


That dongle has a TCXO which is specified to hold the receiver from varying
more than 0.5 PPM. However, the device itself may still have a permanent
offset. I have seen this offset as large as 30+ PPM on some dongles.

To determine the permanent offset for an individual device you need to
compare it, using a 0.0 PPM offset, to a known stable frequency source. The
ideal tool is a service monitor but for most monitoring purposes receiving
a continuous transmitter over the air generally works well enough. NOAA
weather radio or continuous duty trunking control channels are good
candidates.

I haven't played with scope.py for a while, but if I remember right you can
adjust the offset on the fly down in the lower left corner. Observe the
signal of the transmitter in the spectrum display and adjust the offset
until the frequency scale reads properly.

Brett


On Sat, Jun 25, 2016 at 2:45 PM, Sean Kealy superstardodge at yahoo.com
[op25-dev] <op25-dev at yahoogroups.com> wrote:

>
> I think its .5 for the nooelec mini 2 blue rtl, going to try that
>
> On Saturday, June 25, 2016 12:13 PM, "Sean Kealy superstardodge at yahoo.com
> [op25-dev]" <op25-dev at yahoogroups.com> wrote:
>
> Ok thanks, how do I find out my devices ppm?
>
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