[TowerTalk] 43' Vertical - Feed Point Tuner or Shack Tuner?

[jimlux]

Dan Zimmerman N3OX wrote:
> On Sun, Feb 1, 2009 at 10:40 AM, Richard Thorne <rmthorne at suddenlink.net>wrote:
> 
>> I have a vertical in my backyard that I currently feed at the base with
>> an SG-239 200 watt tuner.  I want to increase my power from 100 watts to
>> 400 watts.  In order to accomplish this I either need a tuner at the
>> base like an SG-235 or CG-5000 both expensive.
> 
> 
> A couple of other options:
> 
> Fixed tuned matching networks:
> 
> http://www.n3ox.net/projects/lowbandvert
> 
> or motorize your tuner
> 
> http://www.n3ox.net/projects/servo
> 
> There are more elegant ways to do that, stepper motors, etc.
> 
> You could also do a mix of approaches.... bands where the coax loss isn't
> too bad,  you use a shack tuner, bands where it is unacceptable to you, use
> an external matching network. VK1OD's page could give you a guide to which
> bands are worst, and you could start there.
> 

A remote antenna switch, used to switch among networks or taps in a 
network might be a handy thing with this approach.  One potential bummer 
is that some autotuners aren't happy about passing control signals up 
the coax (if you're using one of the MFJ 1:4 switches).  The 60 Hz might 
cause issues with the fwd/rev power bridge.

Personally, I figure putting the tuner at the feedpoint is your best 
overall option.  You're up against a power issue, but maybe you need to 
look at your actual power and frequency and impedance, and your existing 
tuner will do ok.  The limits on the tuner are a combination of current 
in the inductors and voltage/current on the capacitors.  A bit of 
tinkering with an analysis program might show that it will work ok.  The 
mfr has to pick a sort of compromise power rating for all cases, and you 
might not be in one of the corners (or, you can adjust your antenna a 
bit to make sure).

A 2:1 power difference is only going to be a 1.4:1 voltage/current 
issue.  But I sympathize.. going from the 100-200W class tuner to the 
kilowatt class is a BIG cost shot (hey, it's keeping me from running a 
linear in the car.. I can rationalize the kilobuck for the amp, but 
another kilobuck for the tuner too!... ouch)

Jim, w6rmk