[AMRadio] SP600 CRYSTAL Selectivity

John E. Coleman (ARS WA5BXO) wa5bxo2005 at pctechref.com
Sat Dec 31 14:24:47 EST 2005

	I had an opportunity to go the ham shack last night and decided to
work on the SP600.  The crystal filter doesn't seem to work like BJ and I
think it should.  It works and narrows the band pass alright but doesn't
seem to have a movable notch.  Instead it seems more like a tunable band
pass or IF shift when the phasing capacitor is turned.  BJ and I have been
through the alignment procedure several times using a very stable signal
generator and a frequency counter.  The crystal freq peak seems to be 454.96
and we used the alignment procedures describe in the TO.  Removal of the
crystal and bypassing the resistors and checking the resonances of the two
tank circuits just before the crystal and just after the crystal shows that
they both work and have a good tuning Q when the slugs are adjusted, but
when the whole thing is put back into place the output coil L37 has little
or no effect in any of the three crystal positions.  The resistors in the
circuit check OK as well.

 	Maybe BJ and I are just familiar with the crystal notch movement as
it was in so many of the other Hammarlund,s receivers.  The first three
switch positions don't use the crystal only the last 3 positions are for the
crystal. So maybe it is working correctly.  ANY IDEAS ? 

The Circuit can be seen at

	Put the receiver back in service and got on the air last night
(early morning 2 AM CST 12/31/2005) on 3870 after a SSB QSO signed.  We
talked to Don, K5JRJ in Victoria, Tx for about an hour.  He was on SSB and
BJ and I were on the big AM rig.  We could hear faint signals on 3880 and
3885 about S-1.5.  Another SSB QSO started up on 3875 and we heard no
complaints which I though to be fairly unusual since their lower sideband
and my upper would surely be crossing over when tunning on there frequency
and listening LSB.

Happy New Year to all.

John Coleman

-----Original Message-----
From: amradio-bounces at mailman.qth.net
[mailto:amradio-bounces at mailman.qth.net] On Behalf Of W5OMR/Geoff
Sent: Saturday, December 31, 2005 8:25 AM
To: Mike Duke, K5XU; Discussion of AM Radio
Subject: Re: [AMRadio] 80 Meters Hot

Mike Duke, K5XU wrote:

>It's just after 10 PM central time, and 3880 is full of 80 meter 
>>From Mississippi, I am hearing Ko6NM, Wa3VJB, W5OD, W7ID, and several 
>others, all with reasonable signals, some with amazing signals for my 80 
>meter qth.
>There's also some activity on 3885, but it's not nearly as strong here as 
>the guys on 3880.

I wanted to do a lot more operating than what my body and neighbors 
would allow me to do, last night.

Having been up since 4am that morning, I did get to work 2 stations, but 
both were great contacts;
WA3VJB/Paul in Annapolis, MD and KO6NM/Mike.  I have to say at this time 
that Paul had the typical 'copyable but suffers from QSB, QRM, QRN 
problems that seem to plauge signals from the NorthEast, but when 
Mike/KO6NM broke, (to coin a phrase from K5SWK) "Great Gallopin' Gobs of 
Goose Liver!" coupled with "Holy Mackeral there, Andy!"  40DB/S-9!  What 
a signal.

73 - W5OMR

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