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Old 04-10-2010, 14:30   #1
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Optimum Backstay Antenna Length

Well, we're replacing our standing rigging on Beausoleil, and I thought now would be the time to make sure our new insulated backstay antennas are of the optimum length for the primary bands we'd be using. We're lucky enough to have two antennas, since our backstay is split clear up to the masthead. Right now the total length of the antennas, from the antenna tuners' terminals to the masthead, is about 72-75'. I know that with a random wire tuners like my Icom AH-4 and AT-20, you should avoid half-wave lengths.

Looking at both Sailmail's and Winlink's HF station frequencies, I'm wondering if it's worth it to optimize the length of each backstay so that each is nearer to the length that would work best with most of each service's stations.

Just a cursory look at the frequencies used by Winlink stations tells me that in the ham bands, most stations are in the 40 meter band, followed by 20m, then 30m, 15m and 10m. In the marine SSB spectrum, SailMail stations seem to be fairly spread out over the available 4/6/8/12/16/18/22MHz bands.

Has anyone optimized their lengths, or just made yours as long as you could? I still may go with Bill Trayfor's suggestion of cut dipoles for 20m and 40m for ham, but I might as well make sure the fixed backstays are optimally cut.

You'll also note that our existing lower insulators are pretty high off the deck. I'm assuming that's because of an attempt to keep interaction with the side stays of the mizzen mast to a minimum, but I think the previous owner perhaps forgot that the antenna lead-in wire would still cross those mizzen stays, so I'm going to probably lower them to a more serviceable height off deck.

Any ideas?
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Old 04-10-2010, 16:11   #2
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My backstay antenna is 17.1 metres total length inc.feeder. This gives half wave null at 8.77MHz & 17.54MHz. Seems to work fine on 8MHz nets though.

Formula to calculate (bad) frequency:
F = 300/L x 0.5 x n
F = freq in MHz
L = length in metres
n = natural number 1,2,3 etc.

BTW ICOM ATU manual suggests 15 metres as a good total length to allow use in 1.6 -> 25MHz range.

I've too have noticed a lot of folk have their lower insulator way off the deck & IMO their top one too close to mast. I appreciate the safety issue but eye height + a bit should be enough. In any case to all but the closest stations you are using sky wave so antenna height shouldn't be an issue.
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Old 04-10-2010, 16:14   #3
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i decided i did not want to cut my back stay and went with a gam electronics antenna and it works great - i have a times been a relay for cruiseheimers net and it booms - great reception - can not recommend it enough -
the pundits tell you it does not work and ect ect but it works for us - we relayed the other day from galesville md and had stations from marsh harbor to maine hear us and we talked to them
bahamas last year we subscribe to chris parker and did not have a problem anywhere nor did we with winlink or weather fax from new orleans
check them out - but you need an open mind as most traditionalist dislike them and say they do not work - we know better
and i do not work for the company or get anything out of it - just a happy customer

chuck patty and svsoulmates
on the wall cambridge md
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Old 04-10-2010, 16:16   #4
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oh -- no safety issues with it either = have a quest pole with radar on it and the antenna above that and the antenna feed comes down the quest pole to the turner - could not be simpler

chuck patty and svsoulmates
on the wall cambridge md
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