[R-390] 0.5-8.0 Low Sensitivity (Long)

[Cecil Acuff]

Well that's another tip off that there is a resonance problem in that 
particular tuned circuit.  The slug tuning should never be at it's threaded 
limit to achieve the peak....(it's actually not the peak because you are at 
a physical limit prior to reaching the peak)

I've had to add and sometimes even remove fixed capacitance to get within 
the range of the trimmer.  It's seems to me the inductance value has changed 
from when the can was manufactured.  Maybe there is fine particles of slug 
material worn into the coil form.  Maybe the slug has a chunk missing off 
the bottom of it...who knows.  The factory value of the fixed mica cap is no 
longer correct and requires custom matching to the current circuit 
conditions.  I've had to do it several times and sometimes the effect on 
performance is dramatic because you don't know how far off of the real peak 
you are until you can achieve two distinct peaks with the trimmer capacitor 
at different positions in their rotational range.  It's worth the effort....

Cecil...
----- Original Message ----- 
From: <ToddRoberts2001 at aol.com>
To: <r-390 at mailman.qth.net>
Sent: Monday, September 11, 2006 9:59 AM
Subject: Re: [R-390] 0.5-8.0 Low Sensitivity (Long)


>
> All else works fine now and I'm tempted to just leave well enough alone.
> However, I'm
> puzzled why fresh trimmers and new micas at spec values cannot get two 
> peaks
> during
> alignment.
>
> Got any ideas?
>
> Dan
> WB4GRA
>
> Have you tried screwing in the slugs a few more turns? What happens when 
> you
> screw in the slugs a few more turns? Does the signal continue to peak or 
> does
> it start to fall off? If it starts to fall off then the single peak would
> appear to be near correct even though you only get one peak when the slug 
> is
> maxxed out. I wouldn't worry too much about a single peak if the 
> sensitivity is
> back to normal. 73 Todd WD4NGG
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