[App_rpt-users] GE MASTR II Over Modulation?

[Jesse Lloyd]

Bleeds over as in desensitizes the receivers or you can actually hear audio?

Most modern receiver front-ends have minimal filtering, just a wide
pass-band filter and the IF filters which reject the adjacent channels more
then channels further off frequency.  If you have more than -30 dBm showing
up on any antenna regardless of frequency spacing it'll probably cause
problems.  150 ft is only ~45 dB of isolation, so if you're transmitting
with +45 dBm (32W) less 2 dB of duplexer loss, less 2.5 for cable loss plus
3 dB for repeater antenna, less 45 dB of isolation plus 3 dB for rx antenna
gives about +1.5 dBm which is definitely going to mess up a receiver unless
more filtering is used.  You can play with filters to see what works, but I
suspect you'll need two notch filters to get that down to something that
doesn't effect your receiver.

You need to hook the system to a service analyzer and see if it's actually
over modulating, it's doubtful unless you've injected audio after any
limiter circuits. Running the math it's probably front-end overload, you'd
be best to notch out the transmitter on the effected receivers, you may
have to put a pass filter (and/or notch filter) on the transmitter too to
remove some sideband noise as well, maybe not if it's a clean transmitter.
It's usually a good idea to have balanced reject filtering on both your
transmitter and receiver.

Jesse



On Thu, Oct 12, 2017 at 1:13 PM, Bob Pyke <k6ecm1 at gmail.com> wrote:

> Our RPi controlled radio has an rf spectrum so wide that it bleeds over in
> my Yeasu (150 feet between antennas) when I'm working a distant repeater
> that is more that 200 kHz away from our tx freq. Any suggestions where I
> can look for info on how to deal with this? Our duplexer is the notch type.
>
> Thanks,
> Bob
> k6ecm
> 73
> Sent from my iPhone
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