[R-390] Alignment of the Mechanical Filters and IF with a Spectrum Analyzer

[David Wise]

You'd drive the filter with whatever source impedance it's used to, and same on the other end, loading with the appropriate resistor and using an active probe to isolate the SA's 50-ohm input.

1. I hope you're not thinking of tweaking the resonator disks!  The only official adjustment is the trimmer caps
on the input and output coils of later-production IF modules, and nobody ever did anything but peak them at
the center frequency.  If you sweep a filter and find that the trimmers have a pronounced effect on the skirts,
I guess a compromise would be possible.  Tell us what you see.

2. The LC portion of the R-390A IF chain is fairly broad and not stagger-tuned; perhaps you're thinking of the R-390.

Dave Wise
SWL in Hillsboro Oregon

-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of Mack McCormick
Sent: Thursday, December 13, 2012 9:07 AM
To: R-390 Group
Subject: [R-390] Alignment of the Mechanical Filters and IF with a Spectrum Analyzer

I have a calibrated high quality spectrum analyzer and tracking generator.
Does anyone have experience with using a spectrum analyzer to:

1) *Adjust the mechanical filters? *There is some literature that suggests
just peaking for noise can adversely affect the filter skirts.

2) *Stagger tune the IF?* My thought is that you could look at the overall
spectrum of the IF and make optimal adjustments.

I would of course make sure that I don't load the circuit with the spectrum
analyzer to skew the results.

Does anyone have any experience or suggestions?

-- 
73,

Mack de W4AX
http://w4ax.com