[R-390] R-390A Multiple Signal Peaks

[kirklandb at sympatico.ca]

Passband ripple isn't strictly due to the use of mechanical filters, rather it is the filter choice such as Butterworth (maximally flat passband) 
versus Chebychev (equal ripple passband). If one allows "some" ripple in the passband, then a steeper filter skirt can be obtained for
a given filter order. i.e. one can generate LC filters with ripple as well. 

Of course, one is not restricted to Butterworth/Chebychev/Elliptic filter responses. It may be that the mechanical filter construction
 precludes a Butterworth response - don't know.

> Date: Tue, 17 Aug 2010 12:26:15 -0700
> From: sacramento.cyclist at gmail.com
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] R-390A Multiple Signal Peaks
> 
> It sounds to me like your seeing the passband ripple of the filter in
> use.  I seem to recall a discussion of that feature of mechanical
> filters, especially the wider ones, on this list in years past.  There
> is also, somewhere on the web some good plots of filter response taken
> by one of our own here.  The more organized among us will probably
> post the link shortly.  :)
> 
> Dennis
> 
> On Tue, Aug 17, 2010 at 8:41 AM, Bill Scurlock <k5gcw at sbcglobal.net> wrote:
> > I obtained my first R-390A a few months ago and have been slowly becoming familiar with it.  There is one operational characteristic that I don't know whether it is normal or not.  As the receiver is tuned across a carrier signal, there are multiple peaks observed on the Carrier Level Meter, and also changes in the audio frequency response resulting in some degree of audio distortion regardless of which signal peak is selected by the tuning knob.  The difference in signal level represented by these "peaks" and "dips" in the carrier level meter are somewhere around 100 microvolts or so where I did the testing (at carrier levels of about "40" on the meter).  Visually, the needle on the carrier level meter would swing one or two "needle widths" between signal peaks.  The AGC was on during these tests.
> >
> > There are 6 identifiable signal peaks across the 16Kc. bandwidth position, spacing varies from 1.1 to 3.2 Kc., and the average spacing is 2.52 Kc.  In the 8Kc. bandwidth position, there are also 6 peaks with spacing from 1.2 to 2.5 Kc., and the average spacing is 1.78 Kc.  In the 4Kc. bandwidth position, there are 5 identifiable signal peaks, spacing varies from 0.3 to 1.0 Kc., and the average spacing is 750 cycles.  At 2Kc. bandwidth, only 3 peaks can be seen, and they are about 600 cycles apart.  Only one peak can been observed at the 1Kc. and 0.1Kc. bandwidth positions.
> >
> > I checked the IF tuning, and it is stagger tuned as per instructions.  Although I am suspicious that this may be a factor, I wanted to send this email to the group before I started making changes in the IF tuning arrangement.
> >
> > I have other questions for the group, but wanted to address this one first.
> >
> > Any assistance you can provide will be appreciated.  Thanks.
> >
> > 73, Bill, K5GCW
> 
> -- 
> I've been wondering lately..."Where am I going and why AM I in this
> hand basket??"
> 
> -------------------------
> Dennis L. Wade
> KG6ZI
> Carmichael, CA
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