Choke Balun

VHF Marine Band radios, protocol, radio communication theory, practical advice; AIS; DSC; MMSI; EPIRB.
Tom Hemphill
Posts: 70
Joined: Fri Oct 16, 2015 5:04 pm

Choke Balun

Postby Tom Hemphill » Tue Aug 02, 2022 6:21 pm

I am wondering if my attic-mounted TV antenna (pictured below) with RG-6 coaxial cable might benefit from a choke balun made by creating a coil in the transmission line near the antenna feed point--and I have slack in the cable.

61pd3w6uPIL._AC_SL1500_.jpg
Fig. 1. An attic-mounted TV antenna.
61pd3w6uPIL._AC_SL1500_.jpg (15.69 KiB) Viewed 50 times

jimh
Posts: 10566
Joined: Fri Oct 09, 2015 12:25 pm
Location: Michigan, Lower Peninsula
Contact:

Re: NOAA Weather Radio Reception Report: Northport

Postby jimh » Fri Aug 05, 2022 9:16 am

Hi Tom--most television antennas uses a conventional 300-Ohm to 75-Ohm Balanced-to-Unbalanced balun, and the 75-Ohm transmission line is just led away from the antenna in a manner to keep it near to the antenna centerline or boom.

With UHF television antennas, you can use ferrite beads slipped over the coaxial cable as a choke balun. You can buy split ferrite beads so you do not have to remove the F-connector to slip them over the coaxial cable. See

https://www.digikey.com/en/products/det ... 81/8594058

That bead has an ID of 0.354. An RG-6 cable should have an OD of about 7mm or 0.275-inch.

This smaller bead will be a tight fit; its ID is 6.60mm:

https://www.digikey.com/en/products/det ... 81/8594000

Of you could fashion a coil from the transmission line. The one on my VHF Marine Band antenna was a diameter of about three inches and has two turns.

It can't hurt turn to try a choke balun. Generally suppression of antenna currents on the transmission line tends to improve the pattern of the antenna by keeping everything symmetrical. I have used ferrite bead slip-over hinged beads on some TV antennas I have at my condo which are indoors and are pointing out a window.

Re the TV antenna in my attic, you can see the TV antenna in another article. Visit:

Reception of UHF TV Stations in Northern Leelanau County Michigan
https://continuouswave.com/radio/UHF_TV ... higan.html