Another filter question txing and rxing antennas

[BuffaloJustice]

I know it has been asked but I wanted to see how bad this may get in my case. Since I got my ticket I took the discone off the mast and temporarily retired the scanners. I have a mast mounted j-pole on the eave of the house and want to put the discone in the attic and get the scanners back online. The only space I've got in the attic is on either end, the close side would give about ten feet of vertical separation and five feet of horizontal separation. The far side has the same vertical but about forty feet of horizontal separation, but doubles the coax length. I am currently capable of putting out 50 watts on 2m, and plan to add 6 and 440 antennas as soon as my foot heals, so I'm sure there's going to be overloading.

So with all that, how difficult is it going to be to filter out the amateur frequencies for the scanners. I would just turn off the scanners, but part of the purpose is to be able to listen to public service and transmit on the 2m simultaneously, Skywarn/ARES. Granted when on the repeaters I can use just 5 watts but I would like to be able use high power if/when needed.

Thanks for any and all help

 

[gewecke]

I'm sure you already know this,and I'm not aware of how much room you have but all I can say is separate your receiving from your transmitting antennas as far as you can. I know attic installs are tricky.
N9ZAS

 

[BuffaloJustice]

Yea, I can't get much more height on the mast and when I put the 6m up the base will have to be on the eave so the vertical separation will get worse. I guess the discone will have to go on the other side of the house in the attic.

If the garage were on the other side of the house I could get it way up but that might get a little expensive at this point Any body had any luck getting the power company to convert an overhead power feed to a buried feed? That would solve the height limitation.

 

[zz0468]

I'm sure you could come up with some band-reject filters that would keep the 2 meter transmitter out of the scanners. Going multiband would complicate things, because randomly cascading filters can cause things to get pretty weird. You COULD just try a tuned stub made from coax if overload is a particular problem on a particular band. Keep in mind, however, that a stub or filter for 2 meters is going to have a 3rd harmonic response on 450, and even higher odd harmonics could impact performance on the upper bands.

So your best bet is the separation. So what if it doubles the coax length? Stuffing a small area with antennas and radios is bound to force some compromises. It's not a big deal, but you end up having to make decisions. Overload interference, or reduced performance on one or all of the radios. Run 5 watts into the two meter repeaters, or get desensed on all your scanners while you talk. Pick your poison. Separation and reduced transmitter power are the cheapest, easiest, and the most effective methods.

 

[BuffaloJustice]

Yea I hear ya, 99 percent of the time I'm only using 5 watts. Some desense when I talk doesn't bother me so much as blowing up a scanner on high power, is that something I should be worried about?

 

[zz0468]

Yea I hear ya, 99 percent of the time I'm only using 5 watts. Some desense when I talk doesn't bother me so much as blowing up a scanner on high power, is that something I should be worried about?

No, not if you come up with some reasonable separation between the tx and rx antennas. Just a few feet will cover the damage concern. As to the desense, there are too many variables to predict here. Just keep the ham antennas as far from the scanner antennas as you can, and run with it.