--------------------------------------------------
From: <n8de@thepoint.net>
Sent: Saturday, November 20, 2010 7:06 PM
To: "Jim Thomson" <jim.thom@telus.net>
Cc: <towertalk@contesting.com>
Subject: Re: [TowerTalk] Tune 160/80 Vertical
> Or you can remotely tune the cap .. and bend one rotor blade tip so it
> will short out when fully meshed. Used that on an 80m vertical many
> years ago.
>
> 73
> Don
> N8DE
&&& superb idea! Take the last rotor plate, or one rotor plate that is
easy to get to,
and fold a short, perfect 90 deg to it. Then when fully meshed, the 90 deg
lip will contact
the mating stator plate...and now the cap is shorted out. IF a relay is
used, that relay will
have to have an open circuit peak V rating, that is greater than the peak V
across the cap, in normal
operation on 160m. IE: Xc x current flowing through it, x 1.414.
Later... Jim.
>
>
> Quoting Jim Thomson <jim.thom@telus.net>:
>
>> From: w3oa@roadrunner.com [mailto:w3oa@roadrunner.com]
>> Sent: Saturday, November 20, 2010 11:36 AM
>> To: towertalk@contesting.com
>> Cc: sturpe@gmail.com
>> Subject: Tune 160/80 Vertical
>>
>> I'm helping a friend who has an 80 meter 1/4 wave vertical. At the
>> top, he has a 160 meter trap then a wire extending horizontally for 160
>> meters. It is therefore an inverted L on 160.
>>
>> The SWR on 80 is good and can be adjusted nicely by changing the length
>> of the vertical component. 160 meters, however is somewhat of a
>> problem.
>>
>> The minimum SWR he can achieve on 160 is about 1.7:1. Of course the
>> object here is to lower the SWR on 160. Here are some readings we took
>> with my MFJ -269 antenna analyzer in case this helps anyone.
>>
>> 1.770, Rs 16, Xs 0, SWR 3:1
>> 1.800, Rs 27, Xs 15, SWR 2:1
>> 1.825, Rs 45, Xs 26, SWR 1.7:1
>> 1.85, Rs 79, Xs 31, SWR 1.9:1
>> 1.875, Rs 128, Xs 2, SWR 2.5:1
>>
>> Can anyone point us in the right direction to find a solution?
>>
>> Thanks,
>>
>> Dick, W3OA
>>
>> ## Install a capacitor in series with the feedpoint of the vertical,
>> right at the base. Make the horizontal wire long enough, so the
>> resistive component is 50-60 ohms on the freq you are interested in.
>> At that
>> point you will have some XL. Then tweak the cap so the Xc of the cap
>> will cancel out the XL on 160m. Presto, flat swr on 160m. On 80m,
>> the cap has to be shorted out. No big deal with a suitable spst relay.
>> A buddy used a motor driven 2500 pf cap... and a 100' tall vertical,
>> with an inverted vee type capacity hat on top. This entire mess was
>> suspended on a catenary line, between 2 x trees. It's flat swr across
>> the entire 200 khz.
>> Note, on some vac caps, they have a feature on em, whereby when the cap
>> is fully meshed, and then some, the plates will short out. This
>> saves you having to install a relay across the cap, in cases where you
>> want it
>> shorted out.... as in your dual band set up.
>>
>> ## a padded air variable and relay will also work, with the provisio
>> that the paralleled padder's don't drift about.
>>
>> Later... Jim VE7RF
>>
>>
>> _______________________________________________
>>
>>
>>
>> _______________________________________________
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>> TowerTalk@contesting.com
>> http://lists.contesting.com/mailman/listinfo/towertalk
>>
>
>
>
>
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