Hello, Eddie here. I have a VHF P25 repeater. Having trouble with 100 watt Motorola radios, when they transmit thru the repeater they sound digital, can't understand them. Now here is the kicker, I can get out of the car and transmit on a Motorola portable in the same spot and it talks fine. This happens in different locations and on different 100 watt mobiles. It hasn't happened on a 45 watt mobile. Problem started when we mover repeater to a FM radio tower. Any thoughts would be appreciated.
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Motorola P25 transmit issue
- Thread starter eeeman
- Start date
Couple of random thoughts here...
The first thought that comes to my mind is to double-check the tuning on your duplexer. If everything was just transported to a new site, it's possible the duplexer got knocked around a bit and is now off-frequency, which - if it's only got band-reject - could allow the higher-powered transmitter to bother the receiver. You said it happens at different locations - are any of these locations relatively far away?
And while you're tuning the duplexer, might as well double-check the preselector while you've got the gear.
For that matter - it probably wouldn't hurt to double-check the alignment on the radios and the repeater. At least the frequency alignment.
If it's a Quantar, you can connect WinRSS to the repeater, go to the status screen, and have it show you the real-time RSSI (in dBm I think) of the signal on the receiver and I think you can monitor the P25 BER from there as well.
This also reminds me of an issue we had at a 20kw FM transmitter site. I could put a wattmeter on the feed line and read about 2-3 watts coming in from the antenna system. We made a simple stub filter out of rigid coax, tuned to the frequency of the radio station, put it in-line with the feedline with a T-connector. To this day, I can't be sure that it solved the issue we were having because we did more than one thing that day, but I left it in because it's not hurting anything.
These are all educated guesses, hard to troubleshoot something without being there - let us know how things work out.
The first thought that comes to my mind is to double-check the tuning on your duplexer. If everything was just transported to a new site, it's possible the duplexer got knocked around a bit and is now off-frequency, which - if it's only got band-reject - could allow the higher-powered transmitter to bother the receiver. You said it happens at different locations - are any of these locations relatively far away?
And while you're tuning the duplexer, might as well double-check the preselector while you've got the gear.
For that matter - it probably wouldn't hurt to double-check the alignment on the radios and the repeater. At least the frequency alignment.
If it's a Quantar, you can connect WinRSS to the repeater, go to the status screen, and have it show you the real-time RSSI (in dBm I think) of the signal on the receiver and I think you can monitor the P25 BER from there as well.
This also reminds me of an issue we had at a 20kw FM transmitter site. I could put a wattmeter on the feed line and read about 2-3 watts coming in from the antenna system. We made a simple stub filter out of rigid coax, tuned to the frequency of the radio station, put it in-line with the feedline with a T-connector. To this day, I can't be sure that it solved the issue we were having because we did more than one thing that day, but I left it in because it's not hurting anything.
These are all educated guesses, hard to troubleshoot something without being there - let us know how things work out.
wgbecks
Active Member
It sounds like a "strong signal" condition from your problem description and assuming the 100-watt radios are in good alignment.
What equipment is used for the repeater? IE: Quantar, MMDVM, etc.
So some confusion. You are using P25 correct ? Have you looked at the BER level on the GTR while a mobile is transmitting. If the mobile sounds garbled or distorted then for some reason the base is not decoding properly. I assume mobile to mobile on a simplex channel works fine ? While I agree 100 watts on VHF is alot it should still work. I assume no TTA or amp stuff on the antenna system ? What RFDS do you have for duplexer/combiner and antenna system ? Where does the audio sound garbled ? I assume on a dispatch console ? or a location further away than the rig next to you ?
MTS2000des
5B2_BEE00 Czar
What are you using at "dispatch"? A control station via CCGW? Radio on a desk? Portable? Console connection via microwave? Fiber?
This really requires boots on the ground to properly diagnose and correct. Hobbyists shouldn't be the go to either.
This really requires boots on the ground to properly diagnose and correct. Hobbyists shouldn't be the go to either.
Probably, but a baseline sensitivity is always good to know.
I seriously doubt you are overdriving the GTR.
Did you do an IM study beforehand?
MTS2000des
5B2_BEE00 Czar
"Garbled at dispatch" really says something is wrong with that end if mobiles have no problem. Not knowing what specific hardware and connection (if any) really leaves a ton of variables. One can go down many rabbit holes.
"Problem occurred when repeater moved to new site"....lots of info as KevinC stated: IM study done? Repeater duplexer retuned when on newly sited antenna? Proper RX sensitivity test performed?
"Problem occurred when repeater moved to new site"....lots of info as KevinC stated: IM study done? Repeater duplexer retuned when on newly sited antenna? Proper RX sensitivity test performed?
Thats why I asked about the antenna system. Was it a duplexer ? Seperate antenna's prior ? Alot of missing information. As otehrs asked if at Dispatch how is dispatch connected ? Control Stations ? Consoles ?
towersites
Member
Make sure the mobiles have the encrypting turned off.
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