[Elecraft] Tuning L34 on K2 - The 'Signal to Noise Ratio' method

[Heyder.Family@t-online.de]

After the L34 thread popped up again, I decided to retune L34 once more,
although I'm sure I did this a year ago, hi.

I did almost every step in the procedure as it was suggested several
times before:
Nominal operational temperature, 7.0 Mc birdy, smallest CW filter,
preamp on, AGC on, dummy load etc.

Because I replaced R2 by a pot I measured the DC Voltage with
a DMM at R4 instead. The signal behaviour must be the same there than at R2,
except other levels. But since the absolute level is not so important it
should be ok to have the testpoint there, both sides at R4 are ok to measure.

My goal was to tune L34 for the best signal to noise ratio.
(instead for simply just the biggest signal peak)

When tuning in for the birdy signal (with the frequency dial) I used the
smallest CW Filter setting (0.07) and the SPOT function too.
When tuning out from the birdy (for pure noise measurement) I tuned the
dial abt. 2 Kc off - let's say 7002.0Kc

At first I tuned out from the birdy to measure the noise level over
the whole tuning range of L34:
I did this in small steps of 45 degrees, from L34 tuned completely out until
the core was completely turned down.
For each 45 degree step I noticed the according DC Voltage level in a tabel.

After this I exactly tuned with the dial for the birdy at 7000.0Kc by
using the SPOT function too.
Then I repeated the procedure above with 45 degrees stepwise and noticed
the according DC levels again in the tabel.

After that was completed the tabel showed clearly the core position where
the best signal to noise ratio occurred, which was simply the point with the
biggest voltage difference between the signal- and the noise-level.
I turned the L34 core for this required position and finally did
a 'fine tune' on L34 by using the same principle.
Should notice that I'm not so sure if it is really so important to
be such accurate on this point here!

Now my L34 core is abt. 2 turns down from the outmost position.
Must say that I replaced C182 by 150 pF in earlier times.

Of course if you have an o'scope the procedure to find the
best signal to noise ratio will be much easier.


gl + 72 de Bert   DL8BDF
K2 #433