[TowerTalk] Roller inductor sources

[cgerarden@atomix.com]

I must respectfully disagree with Tom Rauch about the concept of a balun on 
the output side of a tuner vs the input side. I currently have 4 tuners that 
I have basically fried due to legal limit power and mismatches on 450 ohm 
line. These 4 tuners all had output baluns that saturated and got hot, but 
this is not always the failure point. Mostly HV failures at switches or 
caps. 

Only one tuner I have found works great in all 450 ohm line mismatch 
situations. This is a Palstar 1500 BAL. It has 2 roller inductors and a 
balun on the input. The inductors, in series with each side of the output of 
the balun will match a 450 ohm line with high reactance very well. It has a 
switchable cap to move it to the input side of the inductors or output side 
for HI-Z or LOW-Z situations. 

Basically the tuner completes the impedance transformation so the balun is 
not stressed and will not saturate. Keep in mind I am talking about 
situation like a shortened 80 meter doublet loading. 

A critical part of 450 ohm line matching is to vary the feedline too. If you 
really want to match 450 ohm line use a balanced tuner like the Palstar 1500 
BAL. the T and L networks are fine for coax line, but the secret is to 
provide a low SWR into the balun output befor you connect it to the antenna.
this is all based on real world testing. I have a stack of MFJ, Dentron, and 
1 Nye-Viking that I smoked. If you are only runing 100 watts, then almost 
anything will work, but with higher losses. 

Chuck
W0DLE