[R-390] R-390 IF adjustment of .1 1. bandwidth

[David Wise]

I don't remember if the manual has a procedure for these - I'm basing my suggestions on memories of aligning the crystal filters in HP 141T and Tektronix 1L10 Spectrum Analyzers.  There, it's a sweep alignment.  You select wide bandwidth on the filter, then adjust the LC tank for widest bandwidth and symmetrical skirts.  I think that for the neutralizing part you select narrow and go for the deepest notch.  The peak is series resonance, the notch is parallel resonance.  They're slightly different frequencies.  In the middle of the notch, if the caps (C520 and Cstray_xtal) are balanced, nothing gets through at all.  I wouldn't be surprised if C520 and L503 interact and require a couple of cycles to optimize.  Sorry to be vague, but it's been years.

Dave

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Roger Ruszkowski
Sent: Monday, October 21, 2013 3:34 PM
To: R-390 at mailman.qth.net
Subject: [R-390] R-390 IF adjustment of .1 1. bandwidth


Dave,

I see what you say.

We should center the signal generator for a peak through the crystal
as was done originally. Then you align the rest of the IF deck to what
ever that frequency is some where near 455 and well within the mechanical
filter band passes. We then work on getting L503 and the trim cap
to get the best 1Khz we can.

You zero the BFO to the what ever the peak frequency through the .1 kHz 
crystal happens to be. 

What ever the If center is we care not. You just also adjust the VFO 
to zero through the crystal against the BFO. 

So what if the IF deck is not an exact 455. 
Those receivers have worked for at least 60 years that way.

If you have to use a counter, then 1 KHz bandwidth may not be zackly 1.

But I will bet you can't hear the difference.

I think I am diddling in the mud on this point.

How do we best adjust the slug and the cap for a good 1Khz bandwidth?

Roger 



-----Original Message-----
From: David Wise <David_Wise at Phoenix.com>
To: R-390 <R-390 at mailman.qth.net>
Sent: Mon, Oct 21, 2013 6:16 pm
Subject: Re: [R-390] R-390 IF adjustment of .1 1. bandwidth


There isn't any trim to bend the crystal, you just have to take what you get.

L503 is adjusted to resonate at the crystal frequency in order to get the widest 
1kHz bandwidth.  (R502 and R503 "spoil" L503/C524 by a calibrated amount to get 
1kHz or 100Hz respectively.)

I think C520 is adjusted to balance out stray capacitance at the crystal's 
parallel-resonant frequency.

Dave Wise

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On 
Behalf Of Roger Ruszkowski
Sent: Monday, October 21, 2013 1:38 PM
To: R-390 at mailman.qth.net
Subject: [R-390] R-390 IF adjustment of .1 1. bandwith


Bill,

Now that we have counters the question becomes how to 
adjust the trim cap to pull the crystal onto 455 and get the 1Khz
band pass also centered on the 455.

As the TM came before counters, the TM does not 
address this adjustment process.

Fellows how should we conduct this adjustment process?

Roger.

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