Interesting Tuner applet

[James Duffey]

Daan - Here is the match I get for your problem:

Input C 226.6 pF
Coil 1.2 uH
Output C 174.7 pF

SWR 1.0
Percent loss 1.0
dB loss 0.0 (actually this means less than 0.1, teh lowest value the applet
shows)

It is a bit different than yours and the automatch, but it is low none the
less. I get the same automatch that you do.

This points out that although a T-match can achieve a non unique match,
there usually is not a significant difference in loss in these matches.

Here is how I tune a T-match tuner, and the applet as well.

1. Set all controls at maximum.

2. Reduce the inductance untill you see a dip. It might be a shallow dip, or
it may be a deep dip, but  you should see a dip.

3. Reduce the output cap until you see a dip.

4. Reduce the input cap until you see a dip.

5. Tweak the inductor if the dip is not at 1:1.

6. Go back and tweak the output cap, input cap, and inductor to get to the
lowest SWR.

7. If you still have a high SWR, see which control impacts the SWR the most.
Turn it one direction off the dip. Tweak the other two controls in turn to
get a dip. If the SWR is lower than when you started, turn the initial
control in the same direction and tweak the other two controls until you get
a new dip.  Repeat unitl you get the lowest SWR. If the SWR is higher than
before, turn the control in the opposite direction and proceed as above.

8. You may find that only two of the three controls affect the SWR dip. If
that is the case, concentrate on those two.

This all becomes second nature after doing it several times.

I keep a cheat sheet on top of the tuner with the correct settings for each
band/antenna combination. That makes band changes quick. You can also use
those "Post It" pointers that administrative assistants use to show you
where to sign a document to indicate proper settings.

I hope that this helps. - Dr. Megacycle KK6MC/5

--
James R. Duffey KK6MC/5
Cedar Crest NM 87008 DM65

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[Ron D'Eau Claire-2]

While a T-network is not necessarily lossy at moderate impedances, try using
one to load up a short antenna.

For example, a 25 foot end fed wire on 80 meters will show an impedance of
about 3-j550 ohms. A T-network tuner will match it okay, but with a loss of
7 dB! That's a loss of about 79% of the RF passing through the tuner.

That's why I might T-matching network for moderate mismatches in the
vicinity of 50 ohms, but avoid them for wide-range matching of multi-band
antennas, most especially any antenna that is less than 1/4 wavelength long.


A T-match is good at producing a 1:1 SWR to the rig okay, but so will a
dummy load.

The Elecraft ATUs, by the way, use an L-network instead of a T. That's a
whole different "animal" and a lot more efficient.

Ron AC7AC


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