Antenna madness!

Status
Not open for further replies.

Airdorn

Member
Premium Subscriber
Joined
Mar 9, 2008
Messages
428
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

Member
Premium Subscriber
Joined
Feb 19, 2005
Messages
626
Location
NE Wisconsin
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

Member
Joined
Jan 16, 2007
Messages
1,180
Location
Southeastern Virginia
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.
 
Status
Not open for further replies.
Top