[Antennas] 1/4 wave vert,

Thu Aug 21 14:15:13 EDT 2008

Hello Jim,
Your answer is quite interesting.
I always thought that the 50 foot Hy-Tower Hy-Gain 18HT was resonant
in the middle of the band because of the thickness of the base of the
tower. The current model is AV-18HT and in the downloadable pdf
manual it says it is 53 feet. Perhaps 3 feet was added, or my memory
is faulty. We will use 53 feet.
Now I see that it is just the loading of the tower by the added stubs!
With the stubs removed, the Hy-Tower no longer resonantes at 3650 kHz
and needs more length. The formula says it needs 64 feet - which
means that 14 additional feet of "stinger" must be added.
This means that at least the top two secontons of telescoping aluminum
must be removed, and since there is going to be aluminum running now
all the way to the base, it probably all has to be removed.
In the manual it shows 27 foot 9-3/8 inches of extenstion made from
aluminum tubing sticking out of a 24 foot tower - which is a total of
51 feet 9-3/8 inches. Perhaps that is where my 50 feet came from?
In any event, the current manual says the radiator is 51 feet 9-3/8
inches and a length must be added. The lower tower section is three 8
foot (24 ft total) sections which is in cluded in the length.
Do you have someone recipe for which sections of aluminum have to be
replaced and with what lengths?
I remember that I had done come computations of the 40 meter stub, and
that the total length from the tip to the base of the tower was 30
feet 10-1/2 inches - just a bit lower - so evidentally the other
stubs increase the loading to about 33 feet.
As a side note - the verticals seem to work "very well to super" on
their 1/4 wave band, "ok" on their 1/8 wave band, and "not so hot" on
their 1/16 wave band. I call a 1/16 wave vertical a dummy load that
radiates pretty good.
Got the numbers for the tubing, Jim - or a link to them?
73
David Ring, N1EA
On Thu, Aug 21, 2008 at 12:52 PM, Jim Miller <k4sqr at juno.com> wrote:
> Joe;
>> Our 80 meter Hy-Tower customers remove the stubs for 10-40
> and add aluminum to the "stinger" on top for a full size 1/4w vertical.
> They remove the wire in the center, bond the aluminum to the tower at the
> top,
> and feed the base section. The 24' of tower adds to the bandwidth
> with the aluminum. Centered at 3.650, they use them on the entire
> band without any physical stub changes from CW to the DX window.
>> Regards,
>> Jim, K4SQR
> www.comteksystems.com
> Our 19th year of Hybrid Couplers
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