Hi Mike(s),
I'll spreade my comments within the quoted inserts of the
original messages.
To: <towertalk@contesting.com>
>Date: Wed, 30 Dec 1998 05:50:32 -0600
>From: Mike Bragassa <bragassa@hal-pc.org>
>
>Hi Mike: I was thionking like W7WHY's email response; that you
>will have to adjust all of the hi-vswr elements, (reflector /
>directors) including the driven element to affect any change in
>vswr. Thats easier said than done...
Not only is it easier said than done, it isn't a good idea
either. You have absolutely no mechanism (other than pattern
measurements) to determine the correct settings for any of the
parasitic elements. Unless you have some reason to suspect that
one is simply not working due to a fault of some sort, you should
not fool with it. Changing parasitic element dimensions to
modify the feed point impedance is virtually guaranteed to
produce an array that is not set up correctly to produce the
desired directivity.
>
>But you could 'try' the driver first and see what it does. If no
>improvement..then you are gonna' have to crawl out on the boom
>to get to the others!! (Sure!)
Make ALL tuning and matching adjustments to the driven element
_only_. Start with the highest band and work on lower frequency
bands in order of decreasing frequency. Adjustments to the
driven element will have no effect on the pattern of the
antenna. Adjustments to the parasitic elements will definitely
have (mostly unpredictable) effects on the pattern of the
antenna. Do yourself a big favor and just set the parasitic
element dimensions to the manufacturer's recommendations and
leave them there.
73, Eric N7CL
>
>Better yet would be to tilt the antenna...unless you are part
>monkey!
>
>Mike K5UO
>
>At 08:55 AM 12/29/98 -0500, you wrote:
>>
>>Hello,
>>
>>Need information on what others have found in adjusting a
>>TH6DXX for best SWR in a particular part of a band?
>>
>>The TH6DXX used here is set for the CW. On 20, the SWR is as
>>it should be. However, on 15 and 10 meters the lowest SWR is
>>in the phone band - on 15 it is around 21,275 kHz and on 10
>>meters it is around 28,300 kHz. The TH6 is mounted on a 125 ft
>>tower with the guys either Phyllistran(?) or broken by
>>insulators every 51 feet.
>>
>>It was rebuilt, including the traps, using many of the
>>techniques discussed on the reflector - Noalox on the aluminum
>>joints, all stainless steel hardware, lockwashers used under
>>all the bolts or nuts, etc.
>>
>>My present thinking is to just adjust the driven element (I can
>>get to it on the tower) by increasing the distance from the
>>boom to the first trap. Then to shorten the element's tip
>>(outer end) to trap distance by an amount equal to the
>>"increase". The reasoning is by increasing the boom to first
>>trap distance should lower the SWR on all the bands and the
>>reduction of the tip to trap distance would bring 20 meters'
>>back to its present SWR minimum spot.
>>
>>Any and all thoughts are welcome.
>>
>> 73,
>> Mike, K4GMH
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