KX-1 receive passband - any adjustments possible?

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KX-1 receive passband - any adjustments possible?

Barry N1EU
The BFO offset in the KX-1 is fixed at 600hz.  I would hope that the
receive audio passband should be somewhat centered around 600hz.

I recently received KX-1 s/n 2550.  I quickly noticed that the passband
seemed "high" when compared to an older KX-1 I was previously using.  I
looked at the audio from both KX-1's on the pc and confirmed that with
about the same selectivity setting on the front panel, the old KX-1 peak
passband was 350-770hz (okay) and the new KX-1 peak passband was 650-1100hz
(not good).

How would one go about correcting the KX-1 passband?

Thanks & 73,
Barry N1EU
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Re: KX-1 receive passband - any adjustments possible?

Don Wilhelm-4
Barry,

The typical most narrow KX1 receive bandpass is centered somewhere
between 550 Hz and 650 Hz, but can vary as much as 100 Hz on either side
for KX1s that are on the more extreme edges of normal.

I suspect you are checking the passband with a single signal and that
can lead to erroneous results.

To check the centering of the passband, I strongly recommend using a
broadband noise generator at the antenna input and an audio spectrum
analyzer (Spectrogram for example) running on the computer soundcard.  
You can take a look at part 3 of the K2 Dial Calibration article on my
website to understand how to use Spectrogram.
That article also goes into detail about setting the K2 filters, and for
the KX1, that information can be ignored - other than how to observe the
resulting filter passband.

If indeed your filter passband center is as high as 1000 Hz, you should
replace the BFO and IF filter crystals.

Attempting to use a single frequency input signal can be done, but it
takes a lot of point by point audio output measurements, careful tuning
to the next measurement point, and potential error due to AGC. The
broadband signal input is the easy way to do it.  If you do not have a
broadband noise generator like the Elecraft N-Gen, you can build the
simple circuit shown on the webpages of Tom Hammond (SK) N0SS - his
webpage is being maintained at www.n0ss.net.

As one last note - there are no dashes in Elecraft product models. It is
"KX1" instead of "KX-1".  The only exceptions are the mini-modules N-Gen
and 2T-Gen.

73,
Don W3FPR

On 9/2/2012 8:01 PM, Barry N1EU wrote:

> The BFO offset in the KX-1 is fixed at 600hz.  I would hope that the
> receive audio passband should be somewhat centered around 600hz.
>
> I recently received KX-1 s/n 2550.  I quickly noticed that the passband
> seemed "high" when compared to an older KX-1 I was previously using.  I
> looked at the audio from both KX-1's on the pc and confirmed that with
> about the same selectivity setting on the front panel, the old KX-1 peak
> passband was 350-770hz (okay) and the new KX-1 peak passband was 650-1100hz
> (not good).
>
> How would one go about correcting the KX-1 passband?
>

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