[TowerTalk] high power tuners

[david jordan]

Good Ideas,

Current Baluns don't play nice when used as remote baluns.  You really 
need a nice hefty voltage balun.  Fair Radio used to sell a 3kw balun 
kit for less than $15. I built one using #12 stranded teflon coated 
silver wire. Used the MFJ259 and a 200ohm load to tune the balun for 
160m (had to add several feet of wire to get it down there). The balun 
carriers the legal limit and runs cool. I've fed a half wave dipole on 
160m and extended zepp on 160m with this arrangement. Keeping the coax 
run to the balun as short as  possible makes a big difference in what 
the tuner has to deal with...the open wire line is 450 ohm.

This is one of the few areas of ham radio where folks can still tinker 
and play.  I'm glad there's no off the shelf solution!

Enjoy,
dave
wa3gin

Jim Jarvis wrote:

>FWIW, at my MD site, I wanted to have a general purpose utility
>antenna.  Aesthetics played a part.  
>
>Put up an 80m dipole fed with open wire line....perhaps 100' of it.
>Bought a Tentec 238B tuner.  Nice tuner...second one I've owned.
>(much better without the dial cord!)  
>
>First time I've tried the 238 with OWL.  First time I put power into
>it on 40, I saturated the balun core....man, did that smell hot!  
>
>Let's see....40m full wave, center fed....2000 ohms, fed about a 
>wavelength away on the OWL...1200 watts... can we say high voltage?  
>The short form is, the 238 is NOT a high power tuner for balanced
>wire, under all conditions.
>
>Model the driving point impedances on various frequencies, and you'll
>quickly see that the wide range of situations requires extreme caution
>in design.  Radioworks won't sell their 'remote balun' without a serious 
>caveat, for the same reason.    
>
>The short form of this is, you're going to have to model what you want
>to do, and make sure you can handle the wide range of complex impedances
>you'll see.  When you turn the wick up on that amp....you'll find the
>weakest link, for sure.
>
>Jim/n2ea
>
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