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K2 Filter Alignment

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Bernie KF0QS

K2 Filter Alignment

Dear Folks:

I am the proud owner of K2-10 #6922 and, so far, have been operating it exclusively on cw (I am building the SSB option right now, though I am a brass pounder). It is a fine radio and has caused my TS-850S and AL-80 amp to gather a lot of dust.

My only problem has been the filter alignment. I have repeatedly tried to align the filters, and always seem to end up with a situation where the passband of the filters never falls within the passband of the receiver at its maximum bandwidth (I have it set for 150hz). In other words, the received signal, when the receiver is right on it, always seems to fall outside of the 70hz filter (if I tune the receiver to copy the received signal with the 70hz filter in use, and then switch to the 40 and 20hz filters, the signal stays within the bandwith).

The last time I tried to align the filters, I used a noise generator and Spectrogram, and followed Tom Hammond's (N0SS) instructions. After doing this, I always need to turn on the RIT and turn a few hz below the received signal to bring it within the bandwith of the 70hz filter.

What am I doing wrong? For reference purposes, I have my sidetone set for 600hz.

Thanks and 73 de Bernie, KF0QS

Don Wilhelm-4

Re: K2 Filter Alignment

Bernie,

Are you tuning the desired signal to your sidetone pitch - use the SPOT
and match the signals to the same tone - when the two are quite close in
pitch, you will hear a WOW WOW WOW sound of the beat frequency. When
that beat sound slows down to nothing, you are at Zero Beat. Adjust the
AF Gain control (and the ST L menu if needed) to make the amplitude of
the sidetone and the signal about the same to hear that beat note best.

If your tuning is not the problem, then give it another try with
Spectrogram and a noise generator.
Make certain the CW DAC values (or frequencies if you are displaying
that) are lower than the CWrev values.
Also make certain the menu sidetone pitch setting matches the center
frequency you set for FL2, FL3 and FL4. The transmit frequency is
offset by that amount by the firmware.

For FL1, since it is wide, you cannot set its center at your sidetone
pitch, but the passband must be entirely within the Spectrogram
display. Make sure you can see the left side of the passband skirt drop
down significantly before reaching zero frequency. Failure to do that
will cause loss of the Single Signal reception - in other words, you
will hear part of the opposite sideband.

There are also instructions on my website www.w3fpr.com. Look at part 3
of the article on K2 Dial Calibration.

BTW - multiply those widths by 10. That is a 700 Hz filter, not 70 Hz.
The last zero is not displayed.

73,
Don W3FPR

On 12/31/2012 12:42 PM, Bernie KF0QS wrote:

> Dear Folks:
>
> I am the proud owner of K2-10 #6922 and, so far, have been operating it
> exclusively on cw (I am building the SSB option right now, though I am a
> brass pounder). It is a fine radio and has caused my TS-850S and AL-80 amp
> to gather a lot of dust.
>
> My only problem has been the filter alignment. I have repeatedly tried to
> align the filters, and always seem to end up with a situation where the
> passband of the filters never falls within the passband of the receiver at
> its maximum bandwidth (I have it set for 150hz). In other words, the
> received signal, when the receiver is right on it, always seems to fall
> outside of the 70hz filter (if I tune the receiver to copy the received
> signal with the 70hz filter in use, and then switch to the 40 and 20hz
> filters, the signal stays within the bandwith).
>
> The last time I tried to align the filters, I used a noise generator and
> Spectrogram, and followed Tom Hammond's (N0SS) instructions. After doing
> this, I always need to turn on the RIT and turn a few hz below the received
> signal to bring it within the bandwith of the 70hz filter.
>
> What am I doing wrong? For reference purposes, I have my sidetone set for
> 600hz.
>
>

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Bernie KF0QS

Re: K2 Filter Alignment

Don:

Thanks for your reply. I have to admit that I had completely forgotten the "spot" function. I guess my ear was attuned to something different from what the spot function would show. I have found that, if I use the spot function, I am able to keep the received signal within the passband of the filter in use.

I did recheck my dial calibration, and I did the filter alignment all over again. It now seems to work fine. Indeed, I gave it a bit of an acid test during the North American QSO Party last weekend. I would tune into one of the most crowded frequencies, get a signal in the middle of the passband for one of the narrower filters (I do now understand that the filters are 1500khz, 700, 400 and 200khz - sorry for the error), and then try and reply to that signal. It worked perfectly every time. In other words, a signal in the center of the filter passband was pretty close to my transmitted signal.

I wanted to wait a bit before replying because, on a few past occasions when I realigned the filters, the filter alignment seemed to change as time went on. In other words, the received signals seemed to end up more and more out of the passband as time went on. However, at this point, two weeks after I did the latest realignment, everything seems stable and working well.

Thanks so much for your patience and help.

73 de Bernie, KF0QS

Don Wilhelm-4

Re: K2 Filter Alignment

Bernie,

It is good to hear that you have found success.

As far as the filter alignment "instability" that you have alluded to, I
think that impression has other causes - lack of properly zero beating
for one.

I have recently worked on 3 K2s that I had aligned 3 to 5 years ago, and
I find that the settings did not change. The K2 alignment and
calibration settings are quite stable and do not drift over time once
they are properly set. Do it right and it will stay put for a very long
time.

For additional information about setting the filters (and dial
calibration) on your K2, please refer to the K2 Dial Calibration article
on my webpage at www.w3fpr.com.

73,
Don W3FPR

On 1/15/2013 11:33 PM, Bernie KF0QS wrote:

> Don:
>
> Thanks for your reply. I have to admit that I had completely forgotten the
> "spot" function. I guess my ear was attuned to something different from
> what the spot function would show. I have found that, if I use the spot
> function, I am able to keep the received signal within the passband of the
> filter in use.
>
> I did recheck my dial calibration, and I did the filter alignment all over
> again. It now seems to work fine. Indeed, I gave it a bit of an acid test
> during the North American QSO Party last weekend. I would tune into one of
> the most crowded frequencies, get a signal in the middle of the passband for
> one of the narrower filters (I do now understand that the filters are
> 1500khz, 700, 400 and 200khz - sorry for the error), and then try and reply
> to that signal. It worked perfectly every time. In other words, a signal
> in the center of the filter passband was pretty close to my transmitted
> signal.
>
> I wanted to wait a bit before replying because, on a few past occasions when
> I realigned the filters, the filter alignment seemed to change as time went
> on. In other words, the received signals seemed to end up more and more out
> of the passband as time went on. However, at this point, two weeks after I
> did the latest realignment, everything seems stable and working well.
>
> Thanks so much for your patience and help.
>
> 73 de Bernie, KF0QS
>