[R-390] Filter Bandwidth Question

[Ed G]

Thanks all for the comments on my filter question.  Spent more time this morning with the 390A…I am thinking now the issue is basically pilot error.  I had been listening with a fairly new-to-me Hammarlund HC-10 being fed from the 390A IF output.  When I went back to just listening on the basic 390A, I was not noticing any signal level drop when using the .1 bandwidth position.  Careful tuning and audibly zero-beating signals coming from both the 390A and the HC-10, BEFORE adjusting slot frequency, BFO, and passband on the HC-10 resulted in equal signal strength showing on the 390A S-meter when switching bandwidth.  Bottom line is I probably don’t have any problems within the 390A, and I need more usage time with the HC-10/390A combination.

I can say the HC-10 is amazing, and when cascading filters (390A and HC-10) on CW I notice a great improvement in unwanted sideband rejection.  But main frequency tuning is indeed touchy in CW when using the narrow filter settings, but what a wonderfully quiet signal you end up listening to!

--Ed—


Sent from Mail for Windows 10

From: Larry H
Sent: Monday, May 11, 2020 10:21 PM
To: Ed G
Cc: r-390 at mailman.qth.net
Subject: Re: [R-390] Filter Bandwidth Question

Hi Ed,  You are right that the .1, 1, and 2 kc bandwidths use the 2 kc filter.  Sometimes getting the vfo on the center using the .1 b/w is difficult, so try adjusting the kc knob carefully.  What can happen is the 455 kc crystal filter in Z501 will drift over time and nolonger be on 455 kc.  That's why the 1st part of the IF alignment procedure is to set the kc knob on the strongest signal point when in the .1 kc position and set the bfo to 0 there.  The crystal should be ok as you said that the signal strength was ok on the 1 kc position.  The Z501 alignment procedure may need to be done to get the .1 and 1 kc signal levels equal.

Regards, Larry

On Mon, May 11, 2020 at 2:01 PM Ed G <ed.n3cw at gmail.com> wrote:
Hi Folks,
     My Capehart 390A is working mostly FB, but I do notice what would appear to be filter loss when I switch down to the .1 filter bandwidth.  All other filter positions seem to be fine with no difference in signal/S-meter readings when going from 16 KC down to 1 KC.  But when I go to .1 KC signal level does drop down noticeably. I thought the 1 and .1 positions used the same mechanical filter, so perhaps the problem is something else (load resistor)?  Any suggestions on what to check?  Thanks!
--Ed—


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