Gary:
I shunt-feed my tower on 160 and 80M, too, and don't have that problem
with the rotator indicator. I'm running 100W. I think it's because I have
two solenoid-like coils in the rotator control cable. One is just
underneath the rotator support platform at the top of the tower, in the
short piece of cable that goes from the rotator to an 8-pin trailer hitch
connector (from The Wireman) that takes the cable down to the bottom of the
tower, inside the tower structure, not on the outside. This placement might
provide some amount of Faraday cage-like isolation for the cable.
The second solenoid is at that bottom end of the cable where it enters
a steel box on the tower that also contains my arrestors and antenna switch.
Both solenoids are two inches ID and consist of four turns. You can see a
photo here:
http://s83.photobucket.com/albums/j282/ersmar/?action=view¤t=Towerbase.jpg
.
The solenoid is beneath the steel box, on the left. YMMV.
BTW - I have a second trailer-hitch connector inside the box. It's
there so I can bring out the control box from the shack and rotate the
antenna from the base of the tower, like while I'm doing maintenance.
73 de
Gene Smar AD3F
----- Original Message -----
From: "K8RI on TT" <k8ri-on-towertalk@tm.net>
To: <towertalk@contesting.com>
Sent: Sunday, February 13, 2011 1:53 PM
Subject: Re: [TowerTalk] shut fed tower and rotator
> On 2/13/2011 1:25 PM, Gary Slagel wrote:
>> I recently built 2 verticals for 80 and 160 by shuntfeeding my tower.
>> They both seem to load nicely and are broadbanded, partly because of an
>> insufficient radial system.
>>
>> When I transmit on either 160 or 80 the meter on my rotator controller
>> deflects.... this makes sense since I'm running rf right through the
>> rotator. Till now I've run only 100 watts thru the antennas but I'd
>> like to see if the antennas will handle a KW ok. I'm wondering if
>> there's any chance of damage to the rotator (Ham IV) if I do this. I'd
>> guess not but it makes me a little nervous.
>
> It could be coming in on either or both the coax or rotator cable.
> As you are showing a good match, I assume the match is at the tower and
> you are not using a line tuner at the shack.
>
> When operating 75 at roughly 800 to a 1000 watts the LEDs on my
> 6-pack and remote antenna switches would light. At the legal limit they
> were bright enough I was worried about damage. I tried chokes on the
> cables, but nothing changed. Then I added a current balun where the feed
> line between the 75 sloper and the remote antenna switch reached the
> tower. No more interferrence.
>
> The chokes/baluns I used were 5, 2.4" 31 Mix toroids with 5 turns of
> LMR-400.
>
> I'd try one in the rotator cable near the control box to see what happens.
>
> Read Jim Brown's (K9YC) RFI tutorial
> http://www.audiosystemsgroup.com/RFI-Ham.pdf about toroids, RFI, baluns,
> and audio interfacing. It's well worth the time.
>
> 73
>
> Roger (K8RI)
>>
>> Currently 10 watts deflects the meter about 10%. 100 watts deflects it
>> about 25%.
>>
>> Anyone have a thought on this?
>>
>> Thanks,
>>
>> Gary Slagel
>> Hot Springs, SD
>> N0SXX
>> http://marina.fortunecity.com/sanpedro/351
>>
>>
>>
>> _______________________________________________
>>
>>
>>
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>
>
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