[TenTec] Model 238C Tuner Questions
k9yc at audiosystemsgroup.com
Tue Oct 16 12:03:23 EDT 2012
On 10/16/2012 4:19 AM, Richards wrote:
> Does anybody have a simple description of the procedure one should use
> to quickly find the sweet spot?
There's a procedure in the manual, which is not in front of me at this
time, but from memory it goes something like this:
Using small settings for L and C, switch the center knob from its off
setting to high and to low, observing which seems to reduce SWR and use
that setting as a starting point. Now, adjust C and L for reduced SWR.
When you switch the center knob you are adding capacitance, so when you
increase the C with that switch you should retune the capacitor to
minimum and continue.
The trickiest matches to find are those with small values of C -- it can
take a while to figure out whether the switch should be left or right.
In general, high values of L and C are needed on the lower bands, very
small ones on the higher bands.
The Ten Tec tuners DO tend to stay matched over a wider range than most
tuners, but the antenna you describe is not well behaved, and a poor
choice if you have local noise because it is inherently severely
imbalanced. That imbalance puts considerable common mode current on the
feedline, which really needs a choke, but the severe imbalance puts so
much common mode voltage across the choke that VERY high values of
choking Z are required if the choke is to handle high power. OCF
dipoles are notorious for frying chokes.
73, Jim K9YC
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