KX1 Crystal Filter Center Frequency a Little Low

[Roger Marrotte]

I just finished building KX1 #1447.  All went well with the construction.
All seems to be working fine.  This is the second KX1 I've built.  I've also
built three K2s and a K1, all with most options.  I recently built another
company's QRP rig and that was a chore, to say the least, compared with
building the Elecraft rigs.  The center frequency for the crystal filter on
the new KX1 seems to be around 490Hz according to Spectrogram.  Peaking
signals with the filter set to it's narrowest setting shows a center
frequency of about 490Hz with Spectrogram.  I built my first KX1 when they
first came out and I have since sold it and I don't remember what the center
frequency was for that one.  Is this low? Is this normal? Should it be
closer to 600Hz?  Can it be adjusted up closer to 600Hz?  All else works
fine with the radio.  The filter is nice and sharp.  Signals are strong on
both bands.  The rig only has 20 and 40 meters so far.  I did the BFO and
DDS procedures.  Signals seem to be coming in at the right frequencies.
 
Roger, W1EM
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[David Toepfer]

On the low end of the filter it drops down from around 600Hz over most of the
range to around 500Hz.  I am sure others can detail why.

David, K3ZTUE
.


--- Roger Marrotte <[hidden email]> wrote:

> I just finished building KX1 #1447.  All went well with the construction.
> All seems to be working fine.  This is the second KX1 I've built.  I've also
> built three K2s and a K1, all with most options.  I recently built another
> company's QRP rig and that was a chore, to say the least, compared with
> building the Elecraft rigs.  The center frequency for the crystal filter on
> the new KX1 seems to be around 490Hz according to Spectrogram.  Peaking
> signals with the filter set to it's narrowest setting shows a center
> frequency of about 490Hz with Spectrogram.  I built my first KX1 when they
> first came out and I have since sold it and I don't remember what the center
> frequency was for that one.  Is this low? Is this normal? Should it be
> closer to 600Hz?  Can it be adjusted up closer to 600Hz?  All else works
> fine with the radio.  The filter is nice and sharp.  Signals are strong on
> both bands.  The rig only has 20 and 40 meters so far.  I did the BFO and
> DDS procedures.  Signals seem to be coming in at the right frequencies.
>  
> Roger, W1EM
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[Peter Zenker]

Ladder filters vary both their input/output impedance and their midfrequency
when you vary the bandwith. High level rigs like the K2 therefore adjust the
BFO regarding bandwith (Cal Filter), simpler rigs like the KX1 want the OP
to do this by brain :-)

The impedance  change is why you have more or less attenuation, while
varying the bandwith.

72/3 de Peter, DL2FI    
www.qrpproject.de

> -----Ursprüngliche Nachricht-----
> Von: [hidden email]
> [mailto:[hidden email]] Im Auftrag von David Toepfer
> Gesendet: Mittwoch, 26. April 2006 19:11
> An: Roger Marrotte; [hidden email]
> Betreff: Re: [Elecraft] KX1 Crystal Filter Center Frequency a
> Little Low
>
> On the low end of the filter it drops down from around 600Hz
> over most of the range to around 500Hz.  I am sure others can
> detail why.
>
> David, K3ZTUE
> .

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