[Elecraft] [Fwd: Re: SHIFT pitch]

[Don Wilhelm]

Hi everyone,

Lyle reminded me that the K3's built-in  AF voltmeter display can be 
used as a reliable indicator of audio amplitude - it is a true RMS 
reading indication.  He also indicated that a steady carrier can easily 
be used rather than the wideband noise source.  If you use an on-the-air 
signal, be careful not to confuse amplitude changes caused by the filter 
with QSB on the signal.  A QRP transmitter feeding a dummy load would 
probably serve as a steady source of carrier if you do not have a signal 
generator available.

There are several ways to do a relative gain evaluation, and I mentioned 
only the way I am more used to using - I just didn't think of the others 
initially.

73,
Don W3FPR

-------- Original Message --------
Subject: 	Re: [Elecraft] SHIFT pitch
Date: 	Tue, 27 Jan 2009 11:06:20 -0500
From: 	Don Wilhelm <w3fpr at embarqmail.com>
Reply-To: 	don at w3fpr.com
To: 	W5UN <w5un at wt.net>
CC: 	elecraft at mailman.qth.net
References: 	<20090127073502.F72F4652 at dm0205.mta.everyone.net>



I suspect that the filter gain rather than the width is the major cause 
of that behavior.
Try working with the FLx GN setting in the CONFIG menu to see if you can 
obtain a smoother transition.
You could expect the widest filter to have the smallest loss, so start 
with the transition between FL1 and FL2 and when that seems right, move 
on to the FL2 and FL2 transition, etc.

The easiest way to do this is with a broadband noise generator (such as 
the Elecraft NGen) so you have a constant input to the K3 and it would 
be easy to evaluate the audio level using Spectrogram or some other 
audio spectrum analyzer, although a AC DMM connected across the speaker 
would give decent results.

Once you have the filter gains equalized, you can easily change the 
filter offsets if necessary.  While the 8 pole filter offsets are close 
to zero, it is not practical to expect that  they are all exactly zero.

73,
Don W3FPR

W5UN wrote:
> I have three 8 pole filters installed, 2.8, 1.8, and .4 kHz. As I 
> rotate the WIDTH knob, the filters switch in and out at their 
> transition frequencies (as they should). But when that switch occurs, 
> the background noise pitch frequency seems to jump to a different 
> SHIFT frequency setting.  In other words, the transition between 
> filters is not smooth.
>
> I am wondering if all K3's with 8 pole filters do the same thing as mine?
>
> My filter offsets are all set to zero, as that is what I am told the 
> 8 pole filters offsets should be.
>   
>