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[Riku Ylinen]

Have you guys any opinion about clearance between a FM Transmitter antenna (typically max 5 Watts,  87.5-108 MHz) and wireless microphone receiver antennas (470 MHz and up, UHF-R, ULX-P etc.)?

Those frequency ranges are quite far from eachother, but how likely would much stronger FM transmission cause excessive load or interference into the microphone receiver, if being only a few meters from eachother? Many times it would be handy to mount all antennas up to the same mast.

Typically there would be an announcer with a wireless mic within 150 meters or so from the mast and it (among other program) would then be distributed over a much larger area with the FM transmitter. All this outdoors.

What minimum physical distance between antennas should be used? Has anybody experience with this kind of setup, or should I just test it.


Best,

Riku

[Keith Broughton]

Many times it would be handy to mount all antennas up to the same mast.





Riku

While I can't give a specific distance, mounting on the same mast should be avoided.
Considering the FM TX is 5 watts, get it as far away as is practical.

[Mac Kerr]

While I can't give a specific distance, mounting on the same mast should be avoided.
Considering the FM TX is 5 watts, get it as far away as is practical.

Assuming they are both omni antennas, mounting them one above the other will put each antenna in the null of the other. This may actually be better isolation than could be achieved in a reasonable horizontal distance. Antennas with natural gain will have better nulls than 0dB gain whips.

Mac

[Keith Broughton]

Assuming they are both omni antennas, mounting them one above the other will put each antenna in the null of the other. This may actually be better isolation than could be achieved in a reasonable horizontal distance. Antennas with natural gain will have better nulls than 0dB gain whips.

Mac

Good point.

[David Buckley]

A station I do tech work for (though I'm not the RF guy!) has a 1KW TXO FM transmitter, and a STL receiver on 465MHz, and there is also a bunch of stuff for other organisations on 83MHz, 152MHz, and a lot of walkie talkie repeater stuff around 450MHz.  Our STL receiver just works.  The FM Tx has a filter on it to keep it clean.

I'd suggest trying it.  Or, if you want to be more scientific, get an RF guru to work out the products to check no nasties are going to appear, but with just one transmitter, that is relatively unlikely.  Worst case you'll need a filter.

[Jens Palm Bacher]

Have you guys any opinion about clearance between a FM Transmitter antenna (typically max 5 Watts,  87.5-108 MHz) and wireless microphone receiver antennas (470 MHz and up, UHF-R, ULX-P etc.)?

Those frequency ranges are quite far from eachother, but how likely would much stronger FM transmission cause excessive load or interference into the microphone receiver, if being only a few meters from eachother? Many times it would be handy to mount all antennas up to the same mast.

Typically there would be an announcer with a wireless mic within 150 meters or so from the mast and it (among other program) would then be distributed over a much larger area with the FM transmitter. All this outdoors.

What minimum physical distance between antennas should be used? Has anybody experience with this kind of setup, or should I just test it.


Best,

Riku

My guess would be that the RX antenna and front end would provide much of the neded isolation. If you are worried, throw a couple of highpass filter in, and use rx antennas without amplifiers: http://194.75.38.69/pdfs/BHP-500+.pdf

[Riku Ylinen]

Thank you all for sharing your thoughts!

I think I´ll try keepin antennas in their others nulls and also get some additional RF highpass filters to be on the safe side.

[Scott Holtzman]

My guess would be that the RX antenna and front end would provide much of the neded isolation. If you are worried, throw a couple of highpass filter in, and use rx antennas without amplifiers: http://194.75.38.69/pdfs/BHP-500+.pdf

That's interesting, an RC network filter.

I am much more familiar with mechanical filters (cavities) arranged as notch or bandpass filters.

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