[Boatanchors] IF filter question (Sweep Method )

[Gary Schafer]

What are you sweeping it with?

What is the sweep width?

What is the sweep speed?

Are you overdriving it?

Do you have the avc turned off?

How are you coupling the signal in?

Where are you picking the signal off for display, any capacitors in series 
after the detector?

What are you using for a detector?

73
Gary  K4FMX

> -----Original Message-----
> From: boatanchors-bounces at mailman.qth.net [mailto:boatanchors-
> bounces at mailman.qth.net] On Behalf Of K3PID
> Sent: Thursday, October 19, 2006 6:23 PM
> To: boatanchors at mailman.qth.net
> Subject: [Boatanchors] IF filter question (Sweep Method )
> 
> In reference to the IF circuit for my HQ-145. This unit uses a 455 KHz
> crystal filter in the IF chain. It is a more or less classic design with a
> phasing capacitor to balance out the capacitance of the xtal ( or create a
> notch in the passband ) and it has the added feature of a selectivity
> switch
> that adds resistance to the circuit to decrease the Q and thus increase
> the
> passband width.
> 
> 
> Look at the scope traces here:
> http://pg.photos.yahoo.com/ph/rnharsh@sbcglobal.net/detail?.dir=2722re2&.d
> nm=1777re2.jpg
> 
> Problem:
> 1. Changing the circuit Q by switching in resistance should have the
> effect
> of increasing the passband but it appears to just shift the passband with
> no
> significant change in the width.
> 2. Switching OFF the xtal filter looks like it shunts the crystal which
> should just result in the widest possible passband BUT what I am obseving
> is
> a very wide stop band! Yes the curve is inverted with low response accross
> the IF passband. None of the IF transformer adjustments have any effect on
> the shape or height of the curve in the OFF position.
> 
> What am I missing?
> 
> K3PID
> Ron H.
> 
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