Antenna madness!

[Airdorn]

Ok, I was playing around with a faint UHF Motorola system today, and I got some weird results.

Here's my setup:

Scantenna about 30ft on a pole outside, connected to a patch panel next to my scanners with LMR-400 cable.

BCD996T scanner, BCT8 scanner... mounted a few inches apart. I tapped the discriminator on the 996T and that's what I use for Unitrunker. (I also tapped the BCT8, but it's reception is just plain inferior to the 996T, plain and simple.)

Ok, here's the weird part:

With just the antenna coming straight to the 996T, I get a lot of static on the control channel and Unitrunker reports very poor reception.. it fluctuates from maybe 5% to 30%.

But if I put one of those BNC Tee's at the patch panel, then run a short patch from it to the 996T and ALSO to the BCT8, then the signal strength jumps up to 70% - 99%... the control channel also gets very clear.

Now, the BCT8 has to stay OFF for the most consistent signal. If I turn it on and play around with it, then the signal on Unitrunker (from the tap coming from the 996T) may fluctuate wildly.

In any case, I can't seem to monitor that faint UHF system unless I have the scantenna tee'd off at the patch panel.

Can anyone explain to me what's going on here? I figured the "tee to the second scanner" thing would cause interference, NOT improve the reception.

Thanks for any info!

 

[djeplett]

Maybe you are being desensed by a strong signal near to it in frequency and when you attenuate all the signals coming in by introducing a small loss you end up with less front end overload?

Pure WAG on my part...

 

[Don_Burke]

My guess is that you have made a stub which measures an odd multiple of a quarter wavelength at an interfering frequency.

My first suspect on the interfering frequency would be a TV or FM station.