K2 Noise Blanker Slot as Additional IF Amplifier Stage

[Lemkes]

Has anyone thought of, or tried modifying the K2 Noise Blanker to be an
additional K2 IF amplifier stage?

My problem is that when I really, really need the crystal filter, I am
trying to copy a very weak (but readable) CW signal with adjacent S-9 QRM.
When I switch in tighter than about 1200 Hz of crystal filtering, I tend to
lose the target signal due to filter loss. ( Losing the target signal is not
because the BFOs are not properly calibrated).

  When I use just the DSP filter to block the adjacent S-9 QRM, then I still
lose the target DX due to AGC "pumping" (without the IF "roofing" filter).
I'd really like some additional IF gain to compensate for the crystal filter
loss.

  I would try using the Noise Blanker's U1, MC1350, as the added IF stage,
and use U3, the Controller's decoded program lines to adjust U1's AGC input
for front panel gain control.  I could use P1's pin 8, 8R, as power for the
MC1350 so that it's only active on "receive".

  Any feedback would be appreciated.

  73, Dick, AD7AF

Dick and Marty Lemke
PO Box 1038
Ocean Park, WA 98640
Tel. [phone]
www.lemkestudios.com

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[Don Wilhelm-3]

Dick,

Not an IF amplifier stage, but an added IF filter - check out
http://homepages.nildram.co.uk/%7Ebaker/K2_Overview.html to see if that
might address your stated needs.

If you have filter loss at bandwidths less than 1200 Hz, then I would
conclude that you have something wrong with your filter - the filter
typically does not show attenuation until the bandpass is reduced to less
than 200 Hz.  If you are certain your BFO frequencies are correct (the
filter peak is centered on your sidetone pitch), you should not experience
attenuation at reasonable filter widths - if you do, I would suspect that
you have a bad crystal in the filter.

73,
Don W3FPR


> -----Original Message-----

>
> Has anyone thought of, or tried modifying the K2 Noise Blanker to be an
> additional K2 IF amplifier stage?
>
> My problem is that when I really, really need the crystal filter, I am
> trying to copy a very weak (but readable) CW signal with adjacent
> S-9 QRM.
> When I switch in tighter than about 1200 Hz of crystal filtering,
> I tend to
> lose the target signal due to filter loss. ( Losing the target
> signal is not
> because the BFOs are not properly calibrated).
>
>   When I use just the DSP filter to block the adjacent S-9 QRM,
> then I still
> lose the target DX due to AGC "pumping" (without the IF "roofing"
> filter).
> I'd really like some additional IF gain to compensate for the
> crystal filter
> loss.
>
>   I would try using the Noise Blanker's U1, MC1350, as the added
> IF stage,
> and use U3, the Controller's decoded program lines to adjust U1's
> AGC input
> for front panel gain control.  I could use P1's pin 8, 8R, as
> power for the
> MC1350 so that it's only active on "receive".
>
>

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[Steven Pituch]

Hi Dick,
The variable crystal filters in the K2 are very good.  In fact the best I
have ever used.  As Don says, unless you have a bad component, crystal
filtering should be excellent down to about 250 Hz, and the DSP down to 100
Hz before you get a bit of attenuation of signal.  You can even boost the
volume a bit in the DSP adjustments.  I originally had similar problems to
you when I first built the rig  in 1999.  Now I use MixW to check the
filters visually.  You can also use Spectrogram.

Pictures don't lie.  I have some MixW screens shots on my website here.  I
think it would be hard to get these kind of results with most other ham
transceivers.
http://users.ev1.net/~spituch/Steve's%20Page/Radio/RTTY/RTTY.html
>From the photos alone the performance of the filters look phenomenal.

If you adjust the filters while looking at the MixW screen you can get
instant feedback on the adustments you are making and easily adjust the
filters perfectly.  Centering the filters this way is a snap.

One of the reasons for the great popularity of the K2 is that you don't need
to add any filters.

Regards,
Steve, W2MY

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