866 MHz Bi-Quad Scanner Antenna

This is the new scanner antenna I built that's specifically for the San Diego-Imperial County Regional Communication System, with more information at Radio Reference. Specifically, I wanted to monitor the East Zone system. I really wanted the ability to monitor CAL Fire, etc. directly without having to monitor using the internet. My old scanner antenna system wasn't up to the task. It worked - sorta - the signal strength wasn't strong enough for my Pro-2066 scanner to decode the control channel. Plus, 900 MHz pager intermod that would stop the scanner from working. What I needed was some gain towards the site and an antenna that wasn't so broad-banded.

I decided on building a bi-quad antenna instead of a 10 or 12 element beam. Quads are more forgiving on their measurements and much easier to feed. Using an internet site for the calculations, this antenna looked straightforward to build.

I had most of the materials on hand, except for the driven element. Off to my local Lowe's and I picked up a couple sticks of 3/8" brass rod. I cut a sheet of aluminum as the reflector, then bent the rod into two quads that were attached together. Hence the name "bi-quad".

866 Mhz Bi-Quad Antenna
866 MHz Bi-Quad Scanner Antenna

866 MHz Bi-Quad Antenna Reflector
866 MHz Bi-Quad Scanner Antenna Drilled Reflector

866 MHz Bi-Quad Scanner Antenna Feedline
866 MHz Bi-Quad Scanner Antenna Feedline

866 MHz Bi-Quad Scanner Antenna
866 MHz Bi-Quad Scanner Antenna - Front

866 MHz Bi-Quad Scanner Antenna - Side
866 MHz Bi-Quad Scanner Antenna - Side

866 MHz Bi-Quad Scanner Antenna
866 MHz Bi-Quad Scanner Antenna - Installed

The standoffs are 1/2" PVC pipe. Wire ties hold it all together. The feedline is then soldered in the center, I wrapped it with electrical tape. From the back, I squirted in some RTV sealant to seal it up. I made up an RF choke by wrapping 7 turns of the coax using another 1/2" piece of PVC as the form.

This antenna ended up working fantastic. I used my VX5R handheld tuned to the control channel to aim it. It does have rather narrow beamwidth, which is good. The 900 MHz paging system was still there but not as strong. I put a BNC-T between the scanner and the feedline to the antenna. I cut a 5-1/2" piece of coax which is a quarterwave at 932 MHz for a tuned stub. This really knocked down the pager signal and I was able to start decoding the control channel more reliably. This antenna cost $6 to build - I just had to buy the brass rod. Everything else I had on-hand.