The arguments about input vs. output baluns used with antenna tuners makes
one wonder if a balun on both would be advisable?
73,
Gerald K5GW
In a message dated 10/19/2005 3:42:50 P.M. Central Daylight Time,
cgerarden@atomix.com writes:
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
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See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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