GMRS and TV antenna

[PartsMan]

Will a GMRS antenna cause interference with a UHF TV antenna?

If so how far apart would they need to be?

[tweiss3]

It could. If I remember correctly, if looking for vertical isolation, you will need at least 10' vertically to get 60db, and that is directly vertical, one over the other. If going horizontally, I think it was something like 50-60 feet apart to prevent damage at 45 watts, but there may still be interference when transmitting.

[PACNWComms]

Here is a link to a good source for television channel and frequencies used. Vertical separation is the best method if you need two antennas, television and other UHF, in close proximity. I use vertical separation myself in commercial radio (mostly 800 MHz), and for the UHF antenna underneath my VHF antenna of my house. The issue I have is when I use two slot Time Division Multiple Access (TDMA), Motorola Trbo radios in digital mode, you will hear the TDMA "flutter" sound of time slot switching in speakers of many nearby computers, radios, and television sets. This noise will only be noticed if you are using DMR (Digital Mobile Radio) though, so analog GMRS would be fine.

https://www.rfwireless-world.com/Tutorials/TV-channel-frequencies.html

 

[tweiss3]

I just ran the numbers again for 462 MHz.

Vertically, 10' provides 55db, 13' provides 60db and 15' provides 62db isolation. This is just about the minimum isolation a duplexer must provide to be effective. You may get minor desense at that level, but in general, you won't notice on anything with decent front end filtering.

Horizontally, 40' provides 35db, 50' provides 37 db. This is enough to probably not fry a front end of a radio at 50w transmit power, but you will experience desense and interference. If you could achieve 250' of separation horizontally, you would get up to 52db of isolation.

You can check yourself with the Comscope online calculators: Vertical Isolation Horizontal Isolation

[PartsMan]

So are we talking not able to receive radio near the TV antenna, fuzzy TV signal when transmitting GMRS, or frying my TV?

[tweiss3]

At 35db, your 50W transmission would be reduced down to 0.016W, so it shouldn't fry anything in your tv, but your signal/picture will likely drop as you are keyed up, and return immediately after you unkey.