Feed Line Chokes for Vertical Antenna with radials/counterpoise
Feed line chokes for verticals require a special arrangement to isolate the coax feed line from the radials and ground system. Schematically, a good feed line choke for verticals with radials should be built as follows:
Our CUV-1-1500 and CUV-1-5000 feed line chokes are all internally connected to isolate the coax feed line as shown above.
Th CUV-1-1500 unun is a common mode feed line choke for vertical antennas with radials that need to be isolated from the coaxial feed line to keep common mode current from using the coaxial braid as another radial. Very effective with high choking of 1K-5K from 1.8-61 MHz and also incorporates two side studs/wingnut terminals for radial or ground connection at the antenna while isolating the coax feed line braid from the radials via the internal common mode feed line choke. Top terminal with stud/wingnut for vertical connection enclosed in a 4″ x 4″ x 2″ box..
To reduce receiver common mode noise for long runs of coax to your antenna, use a MC-1-1500 or CU-1-1500 feed line choke at the station end of the coax.
Testimonial
Hi Bob,
Radio: Flex-6700 running barefoot -10 to 100 Watts max.
Antenna: MFJ-1216 – 160/80 meter OCFD wire antenna with matching network.
Elevation: Over 60 feet AGL – fully extended.
Installed: Mid November 2013
I operate mainly on the digital modes running less than 50 Watts. All of the sudden after a few days operating with this antenna, I start to have RFI and my radio was acting up; such as changing bands, SWR changing values, radio failures and turning off. However, when I used my Hy-Gain 18 HT vertical on the same band none of the abnormality occurred.
I contacted MFJ and confirm that what I was noticing was a failure of their “matching network” AKA balun. They offered no solutions. Then I contacted Palomar Engineers and bought the 1:1 new toroid RF beads. I called Palomar Engineers and I happened to talked to you directly; regarding the on going issue with the MFJ antenna. I found out that the 1:1 balun was not what I needed (I was miss-informed by MFJ that it was 1:1 matching network.)
You offered to make the required balun 4:1 and the rest is history.
Here are my findings:
- No more RFI displayed on the monitors.
- Radio not acting up or turning off.
- The SWR at 160/80 meter is 1.2:1
- No antenna tuner required. (radio goes to Bypass automatically.)
- Worst SWR is on 10 meter with a 2:1 but still usable, with antenna tuner 1.5.
- One happy OCFD user!
Thanks to Palomar Engineers design and engineering for solving this issue.
73, Ernest – W4EG