[TowerTalk] HF Beam Questions...
Jon Ogden
na9d at speakeasy.net
Mon Sep 29 23:24:09 EDT 2003
I think I may have found part of my problem.
Tonight I climbed the tower and inspected the feed to the Skyhawk. One
of the feed straps coming from the balun was touching the outer part of
the driven element. From what I can tell, the feed straps and the
outer part of the element should not be shorting out as where the
straps attach are into dielectric. I loosened the saddle clamps on the
driven element and moved it slightly.
Now, when I tune up on 20m, my SWR is pretty much at 1.4:1 or so across
the band. 15m is very good except for the lower end of the band where
it rises to 1.7 or 1.8:1. Ten meters still behaves pretty much like
before. Good SWR up higher, but bad in the lower part.
But the big difference seems now to be that I can hear the antenna
pattern when turning the antenna and listening to stations. There is
no definitely nulls and definitely a f/b ratio. So perhaps I was
basically shorting out half the antenna. I think my 10m SWR issue is
likely related to my conductive guy wires. These will be replaced next
spring with fiberglass rod.
If anyone reading can give me any opinions/back me up on my findings,
that would help.
Thanks es 73,
Jon
NA9D
On Monday, Sep 29, 2003, at 09:27 America/Chicago, na9d at speakeasy.net
wrote:
> Hi all,
>
> This past weekend, I was finally able to put up my Bencher Skyhawk
> beam that I'd purchased from another ham last spring. Now I have some
> questions!
>
> The beam is mounted at a height about 53 feet. Above it, I have
> stacked the following antennas: 11 element 2m beam, 17 element 432
> MHz beam, 3 element 6 meter beam (in that order).
>
> Each antenna is approximately 2.5 to 3 feet above the one below it.
> Also on the very top is a Comet VHF/UHF vertical.
>
> The tower is guyed Rohn 25. At present, I have EHS guy wires that
> have been broken up with one insulator on most of the guys but 2
> insulators on the longest guy leg. It's not ideal and I plan on
> putting up non-conductive guys probably next spring.
>
> My Skyhawk's SWR on 20 meters is about 1.6:1 or so across the band.
> On 15 meters it looks quite good except for the lower portion of the
> CW band. On 10 meters the SWR looks fine higher in the band but below
> 28.4 MHz, the SWR goes above 2:1.
>
> My question is are the VHF antennas above the Skyhawk affecting the
> SWR? Or could it be the guy wires or could it be both? It seems like
> I remembered reading here or somewhere that with stacked beams, ones
> that are non-resonant at the frequency of interest will really appear
> to have no affect. That's kind of the principal used when
> manufacturers put effectively 3 monoband Yagis on one boom with three
> feedlines. But are these beams adding excess capacitance?
>
> Is there anything that can be done?
>
> Secondly, I don't seem to have that great of a front to back ratio
> with the antenna. One day of playing around with it isn't much for
> sure. But I was expecting the see a more dramatic drop in signal
> strength between stations on the front of the beam vs. the back. I
> know S-meter's aren't all that accurate, but I seem to get somewhere
> between 1 to 2 S units in f/b ratio. Yet, the beam is spec'd at 20
> dB. I don't seem to hear a 20 dB drop in signal strength. I've never
> had a beam like this (previously had a TA-33) so I don't know what
> really to expect or look for. Maybe I am seeing what I should be
> seeing....
>
> Could all the other hardware up there be screwing up the antenna
> pattern as well?
>
> Maybe there is nothing to be done and I just have to live with things
> as a compromise setup (I don't have the real estate to put up another
> tower for VHF/UHF).
>
> Any advice or help would be greatly appreciated.
>
> Thanks and 73,
>
> Jon
> NA9D
>
>
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>
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>
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-------------------------------------
Jon Ogden
NA9D (ex: KE9NA)
Citizen of the People's Democratic Republik of Illinois
Life Member: ARRL, NRA
Member: AMSAT, DXCC
Ham Radio Webpage: http://www.qsl.net/na9d <- Updated on 1/12/03!!!
Digital Photography Page: http://homepage.mac.com/jogden
"Right is right, even if everyone is against it; and wrong is wrong,
even if everyone is for it."
- William
Penn
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