Baluns and Tri-band Beams

[WA2SQQ]

I’ve got an interesting question about my Mosley TA-33 tri-band beam. About 40 years ago it was suggested to me by a friend to feed the driven element through a 1:1 balun. To do this, the grounding strap that attached one side of the driven element to the boom had to be removed.

Well, it’s been that way for 40 years seems to work fine.

The other night I overheard a QSO about this subject where it was suggested that the balun essentially isolates the boom and the other two elements from the antenna system. The person claimed that by removing the balun he increased the F/B ratio of the antenna. Anyone have any thoughts or comments on this?  

[Jim, W5JO]

The manual for the antenna explains that.  If you don't have the manual you can find it on Mosley's site.

[WA2SQQ]

Actually the manual isn't on their site, but I requested a copy and received it via e-mail. Manual does suggest using a bulun when another antenna (like a 2 Mtr) is closer than 8ft. Mine is 6 ft away.  Called them and they said, "we don't recommend using a balun" They explained that one side of driven element is grounded to the boom to intentionally create an unbalanced antenna, so it can be fed with coax. "We don't recommend a balun, because they can go bad and introduce loss". It's interesting that they don't talk about using one when there is a nearby antenna.

When I asked them about keeping RF off the coax they suggested 5 turns of coax in a 6" diameter as close to feedpoint as possible. Refused to comment on what might occur feeding the way I have been for 35 years!

[Pete, WA2CWA]

I've been using a Wilson System 1 tri-band beam for the last 37 years. When I originally installed it, I also installed a Hy-Gain balun at the feed point. I didn't want to add a large coiled clump of coax at the feed point. Above the beam, roughly 6 feet, is also mounted a 6 element 6 meter beam on a 31 foot boom. Above that is a 2 meter beam also on a roughly 30 foot boom. There was no interaction between the tri-bander and the antennas above it. Around 2005, I replaced the Hy-Gain balun (housing was cracking in several places) with a DX-Engineering version in a metal waterproof case. When securing the coax near the top of the tower, there were no issues with SWR and the close proximity of the coax shield to the metal tower.

[wb1ead]

SQQ..I have the same tri-band yagi here..it sits by itself on a homemade tilt-up wooden tower..I got this several years ago and found that I could not load/match this antenna only with my Kenwood tuner..it showed at best 1.8.1 on 10mtrs and well over 2.1 on the other two bands with no tuning..I removed the grounding strap and my SWR went dramatically down..worst case was 20mtrs and that was 1.7.1 without a tuner..in other words no tuner was really required at all on both 10 and 15 after the strap was removed..even on the hi end..AM portion..now others I have chatted with tell me the opposite so whatever..I DID try a balun after but ended up in the same predicament as b/4 I removed the ground strap..??..anyhoo there is no balun here and no ground strap either..working AM or the occasional DX is no big deal now and I still haven't invested in a linear amp..dat's my story ur mileage may vary  73 de DAVE

[Jim, W5JO]

If you want to keep RF off your coax get the large beads that fits your coax from Palomar recommended for the frequency coverage, you can avoid the coil of coax.

[WBear2GCR]

It's a parasitic antenna - I'm no antenna guru, but I don't see how the removal of the driven element from "ground" changes the front to back at all. After all, why have the second half of the driven element on ground to begin with? Hacksaw it off! If it is grounded, it can't have any use or effect, right-o??