[Elecraft] Re L34 Adjustment

Fri Nov 1 12:27:00 2002

Okay, Mia Culpa "big time"! 

After Peter in England and Ron in New Zealand both had trouble
duplicating my L34 adjustment, I spent my coffee time this morning
digging through the Elecraft archives for Gary Surrency's original
"procedure" that was trying to recall. I turned up the applicable part
of his message quoted by someone else back on October 17, 2000 under "A
few questions about C182 and the alignment of L34". 

Here's what Gary is quoted as having written:

>7. If L34 does not have a definite but broad peak, then inspect C182 to
>see if it is a 180pF cap. 270pF was used in the earlier kits, and in
some
>cases C182 must be lowered to 150pF or less. The peak is easiest to see
>on a DMM, connected to the LM380N-8 side of R20 on the Control Board.
Set
>it for AC volts and tune to the 7.0MHz birdie.

I suspect that is the message I was remembering. Note that he is NOT
measuring the AGC voltage as I did, but is measuring the audio output
from the audio amplifier - just what those using Spectrogram are doing
but by using a DMM the peak is perhaps a bit easier to 'see'. 

Making the adjustment by monitoring the AGC voltage works for me. I'm
guessing as to why it shows up as a dip in the voltage on wide
bandwidths and a peak on narrow bandwidths.  I can see the "noise" hump
clearly on Spectrogram if I'm watching the audio spectrum while doing
the adjustment. The "peak" in the response is when the noise is pretty
evenly distributed across the passband around the 'base' of the spike on
spectrogram that is the 7 MHz birdie. 

In any event, my apologies for have gotten Gary's procedure wrong. I'll
print this one out and add it to my fat envelope of "mods and notes for
keeping the K2 in top form!".  But first, I need a crowbar to get my
foot out of my mouth...

Ron AC7AC
K2 # 1289
                               ---------

Now I admit to being really confused. I do not notice any point of L34's
travel where it produces a dip in the R2 reading. I'm still not clear
how it can. If L34 is adjusted in order to peak the birdie, then surely
the AGC volts will increase.

Maybe (for some reason) I don't have enough adjustment available on my
L34, but I see no point at which the birdie becomes strong enough to
suppress the noise. Even if it did, then the AGC voltage the birdie
generates would have to be initially equal to, and then greater than,
that generated by the noise (otherwise it isn't going to suppress the
noise). So where/how can a dip occur?
-- 
72, peter g3xjs

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