Just because a tuner has a balun on its input, its own circuit can still
be unbalanced (like an L net). That might still work on many balanced
antennas if you lift the ground side of the L net with the input balun,
but the usual problem at 160m is not enough L and C in a tuner network.
If you had enough L and C to hit all of 160m, you probably have too much
minimum L and C for 10m. Manufacturers tend to favor using components
for the bands that are not so expensive as big caps and inductors for
160m optimized operation.
L. B. Cebik, W4RNL, (sk), found that the old Zepp feed, where a balanced
line has one wire open at the end of the dipole and the other feeding
the end, only had 10 per cent imbalance currents in the feeder back at
the shack. Thus, you almost operate a balanced line. Whether that
works on the band depends on how close you are to the limits of the
tuner, which is the L and C issue, and the feeder length possibly
getting into an impedance transformation. The other issue is
ultimately, if the unbalance currents couple into the shack. You don't
want the outer surface of the coax shield on the rig side of the input
balun picking up any stray RF.
Yes, there are voltage limits to insulators that might operate fine at
100 watts but when fed from an amplifier, you reach some high voltages
at the antenna, again depending on impedance and all the system issues,
(feeder impedance transformation action, etc.) Even auxillary issues
like dirt or dust on an antenna insulator could make it break down at
less voltage than when new.
-Stuart Rohre
K5KVH
Bob McGraw - K4TAX wrote:
OK I'll accept the fact that the Palstar tuner uses a 1:1 balun on the
input. Now that raises the question, and I guess I could have researched
it, but then is the Palstar tuner a balanced tuner? As I recall you have a
balanced load connected to it.
One other thought is the fact that the balun is not providing adequate
isolation on 160M, thus current is flowing on the outside of the coax, thus
the SWR meter will certainly misbehave under this condition and the amp
might actually take off into an oscillation.
Or there is come component breaking down in the tuner or the antenna. I've
known of one instance where the antenna center insulator broke down at high
power but showed normal conditions at low power.
Just a few thoughts.
73
Bob, K4TAX
----- Original Message -----
From: "Jeff" <n3jbh@yahoo.com>
To: <tentec@contesting.com>
Sent: Wednesday, March 18, 2009 5:20 PM
Subject: [TenTec] Problem on 160 meters, Whats up? Thanks !
Hey might most gracious and sincere thanks too every one that responded.
Paul from Palstar insisted that it was not his balun but seems every one
else and i do mean EVERY ONE ELSE And that was over 45 folks think it was. I
guess i know what to think of that matter now.
Now who Makes the Best 1:1 Balun hi hi.. Jeff
2.nd Corinthians 3
Now the Lord is that Spirit: and where the Spirit of the Lord [is],
there [is] liberty.
.
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