[TowerTalk] Help with Force 12 C3S 10-Meter Adjustments

[Bob K6UJ]

Hi Jim,
What I did was note the resonant frequency at 70 feet before finishing securing 
to the mast then lowering it down and sat it on saw horses.  Took note of the new 
resonant freq on the saw horses and adjusted the tips to increase the resonant 
freq on the saw horses the same amount that was needed at 70 feet.  It turned out to be right where I wanted it down on the CW end when I raised it up to 70 feet. 
I was thinking if this did not work out I would hoist it up to about 15 feet on some of the fiberglass military poles I have that you described  and adjust there but I was lucky and this worked fine.

BobK6UJ

      From: Jim Brown <jim at audiosystemsgroup.com>
 To: towertalk at contesting.com 
 Sent: Sunday, November 12, 2017 2:23 PM
 Subject: Re: [TowerTalk] Help with Force 12 C3S 10-Meter Adjustments
   
On 11/12/2017 1:49 PM, Bob K6UJ wrote:
> What I did was make sure
> the driver tube was well lubed with Penetrox and slid it out in 1/2 " increments tillit got down where it was good down in the CW end of the band

Of course. But the tricky part is being able to rig the antenna so that 
SWR can be measured at sufficient height to remove ground influence on 
the tuning AND the so that it can easily lower it for adjustments. Or 
access the adjustments from a tall A-frame ladder while it's in the air. 
While adjusting a very different 4-el for 10M, I found that the 
frequency of lowest SWR went DOWN as I raised the antenna, contrary to 
what usually happens with a simpler antenna like a dipole.

A rigging method we often use for portable operations like CQP, 7QP, and 
FD uses the 4-ft 2-in o.d. surplus military mast sections in combination 
with a tripod base fitting. If the "legs" are two elements tall, 
additional mast sections can be pushed up through the center of the 
tripod fitting. We use this to get a C3SS up 20-25 ft. We first learned 
of this method from a talk that K7JA did at Visalia several years ago.

73, Jim K9YC

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