Using an already installed antenna..

[cwhill]

My apologies if this is ridiculous. I feel like I know the answer here (definitely a NO) but wanted to check. At my location where I run my scanner at my desk we have an already installed antenna on the roof of the building. It comes down into my office via very heavy coax and is used only a few times a day for our in daily comms. It connects to a 50 watt repeater in my rack. That repeater is about 10 feet from my desk. Are there any reliable splitters that would prevent transmit power back to a scanner? Basically can I unplug the antenna at the back of the repeater, plug in like an electrical gate to prevent power out the side that I'd plug into my scanner. This would allow me to use the roof mounted antenna for my scanner without having to put another one up there and run 100 feet of cable etc. It drives my nuts because I know it's up there and so infrequently used and my reception would be soo much better that high and in the clear. It's a VHF antenna and I scan VHF in a rural area. Thanks for any thoughts.

 

[kb5udf]

The gear you would need to do this correctly would probably cost more (alot) then a new run of rg8 and a hobby grade antenna. On the other hand, if the use of the repeater were some how very regimented to a few known times per day, you could conceivably put in a coax switch and switch the repeater and the scanner manually in line with the antenna, but only 1 would work at a time.

 

[mmckenna]

Not really.

You could do a diplexer. If your repeater was UHF, you could split off VHF and connect that to your scanner. The UHF repeater antenna isn't going to work well on VHF, and the diplexer would split off everything for a big chunk of the band to the repeater, essentially making the scanner deaf on whatever band the repeater used.
Plus, installing anything in line with the repeater antenna will impact it's performance. You may find that they wouldn't take kindly to you reducing it's performance for a scanner.
Probably best not to do that.

The problem with coax switches is that they get forgotten about, and left in the wrong position. Or, someone doesn't know what it's for and starts messing with it. Probably not a wise idea to touch the repeater system at all.

As kb5udf said above, just get some halfway decent coax and run it up to the roof. Use a separate scanner antenna, and make sure it's spaced well away from the repeater antenna.

 

[cwhill]

Thank you. I had a feeling any solution would be far more expensive then a new run of cable, lighting isolator etc..
Also these old building I'm reluctant to go near the rubber roof seal with anything for mounting another antenna plus a boom lift to attach the new cable run to the brick appropriately. I'll just keep my external ground level antenna.