[App_rpt-users] GE MASTR II Over Modulation?

[Bob Pyke]

I'm guessing 75-100 watts on the repeater PA. I can hear intelligible audio (sounds like it is in the bottom of a well) when listening to the other repeater, 240 kHz separation, on my Yeasu. I'm sure the modulation is correct for GE, established with the Allstar setup, but can check with my service monitor. I looked at it on my SDR receiver, and it looks like a lot of rf drive... perhaps just too close at about 150 ft.

Thanks,
Bob
k6ecm
73
Sent from my iPhone

> On Oct 12, 2017, at 1:40 PM, Jesse Lloyd <ve7lyd at gmail.com> wrote:
> 
> 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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