Co-locating 70cm/440 repeater with broadcast FM

[prcguy]

Running a UHF Motorola MSF5000 ham repeater with the stock internal duplexer on the same tower with a 50 kW FM and 9 kW UHF TV transmitter (590 MHz) with no issues. The 2 meter APRS digi at this site did benefit from a coaxial stub notch filter to knock down the FM station a bit.

The APRS radio is a ham radio with no other filtering than the notch?

 

[kf8yk]

The APRS radio is a ham radio with no other filtering than the notch?

XTL5000

 

[kayn1n32008]

Repeater we have on hand is a Hytera Rd982, which was working happily at a site with cell service and a commercial repeater system.

A cell site & LMR co-locate is a far cry from co-locating with a multi-kilowatt broadcast transmitter. Never played with Hytera repeaters, so I can't comment on it, other than to say, it's not on the list of repeaters I would recommend.

Roger that on the fusion repeaters, I avoid that like the plague.

Excellent. Calling them junk is being quite polite.

Currently I have on a hand a 4 cavity Motorola duplexer with dual shielded jumpers;

I'm guessing it's got PL-259/SO-239 connectors? Yeah, I would be looking at, as a minimum, a 6x 6" cavity, BpBr duplexer from Sinclair/TxRx Systems or other reputable company with a minimum of 100dB of isolation. Possibly adding a broadcast band notch filter, or additional band pass filtering between the repeater and duplexer. Even being 300 odd MHz away, you are going to see power from the broadcast transmitter at the input of your duplexer. You want to keep ALL that broadcast transmitters signal away from both your receiver AND the PA. A dual stage isolator on the transmit side is something you want to seriously consider, even if it is to just save your PA in the even of a catastrophic failure of your RF chain after the isolator. Ensure you have a dummy load rated to handle everything the isolator will potentially be sending it. You can't over do it on the dummy load rating.

 

[ad8g]

We've got a 2m repeater at an FM broadcast site, I think it's 20 or 25kW. Our repeater antennas (4 of them coupled with a phasing harness) are relatively close to the FM tx antenna up top.

Was previously an MSR2000, is now a Quantar. Phelps-Dodge duplexer. We do have measurable RF (up to 1W if I remember correctly) coming back down the feedline, so we had a stub filter tuned to the FM station frequency and we use a circulator with a dummy load just in case.

Not sure how necessary the stub filter was, but I removed it when we changed to the Quantar, it doesn't see a measurable noise floor difference or change in sensitivity with or without the filter.

Bottom line: Yes, if you have a good quality repeater, even if it's older, and at least a halfway-decent duplexer, you're probably fine.

The worst setup might be something like a Yaesu DR-2X repeater

Say no more

 

[KF0NYL]

It also depends on how clean the radio station's setup is. A dirty setup will cause all kinds of problems from 144 MHz through 900 MHz.

We have a small local FM station whose tower is extremely dirty. It will interfere with 2m mobile radios while receiving when close to the station. I've even had the station's broadcast come through my dual band radio a couple of times.

Years ago I helped a friend with his wireless internet company. His radios were all 900 MHz. He had some on that station's tower and we had to pull them off right away as they were totally useless with all of the noise from the station's FM transmissions.