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Author Topic: KX1 sidetone problem  (Read 228 times)

KO6WL

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KX1 sidetone problem
« on: November 21, 2020, 09:49:44 AM »

The sidetone's pitch doesn't sound clear to my ear. Achieving zero beat is therefore challenging. Does anyone else experience this? I read one post that said the sidetone is a square wave. Is that the problem I am hearing?

Is there a mod that adds some musicality to the sidetone?

I know there is a small circuit board kit that one can add that has an LED light up when one has zero beat. I bought one, but never built it.
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WA6BJH

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Re: KX1 sidetone problem
« Reply #1 on: November 21, 2020, 11:24:07 AM »

I tuned my KX1 by zero-beating the signal, or getting close, and then tuning 600 Hz up or down depending on the band.  That seemed to work for me.  And it was close enough.

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KL7CW

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Re: KX1 sidetone problem
« Reply #2 on: November 21, 2020, 11:39:52 AM »

I have made thousands of QSO's with my KX-1 and never had any problem "zero beating" , but we all have different ears.  If the monitor tone is in fact a square wave, then I would expect energy at 600 Hz, 1800 Hz, and even possibly higher frequencies.  If this is the case, then something as simple as a capacitor across the audio chain somewhere which would attenuate 1800 Hz significantly, but have little effect on 600 Hz...just experiment.  Might even be able to put it in the headphone cord.  I think this would help your normal CW reception, since it would cut off some of the high frequency hiss (and QRM) without the need to crank down the crystal filter too much.  You could build an external 600 Hz oscillator, and mix it with the headphone feed, and set the tone level to match typical signals.  However many of my non musician friends, just cannot match pitches easily of even a pure sine wave, so I really suspect the little zero beat indicator would be the best solution.  My K3S has a tuning indicator which seems to work just fine, but I usually just "know" when the signal is at 600 Hz, even without the side tone turned on.  I built a somewhat similar circuit to the KX-1 tuning indicator with different parts, and it worked fine for another project in nearly any on the air conditions.  Another idea, the KX-1 would probably benefit from a sharp external audio filter which you could switch in and out.  If it was set to a very sharp setting (like less than 100 Hz), You could just tune the signal for maximum volume and probably be within 50 Hz, which is plenty close 99 % of the time.  This filter, may be useful occasionally since we all know the shape of the crystal response is not ideal at all settings.  Personally if I did not have good pitch matching ability ( most hams do not) then I would go for the LED indicator.  You might even be able to use it externally if you do not want to wire it into your rig.
                 Enjoy your KX-1     Rick  KL7CW
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KL7CW

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Re: KX1 sidetone problem
« Reply #3 on: November 21, 2020, 06:47:54 PM »

The KX-1 crystal filter seems to do an OK job down to about a BW setting of 750 Hz and its response peaks approximately at 600 Hz.  I believe adding a audio filter perhaps 100 to 200 Hz wide would improve CW reception and would make it possible to tune close to the correct frequency.  I built and modified a rig for a friend which had an audio filter BW of about 200 Hz I believe.  Either of us could simply tune a signal to maximum volume and be close enough to just call him.  I doubt that the error was much more than perhaps 50 Hz, and even a 100 Hz error would not usually reduce your ability to get an answer.  Many of us enjoy a crystal filter BW of around 500 to 1000 Hz for casual operation and even some challenging work, so supplementing that with a narrow audio filter for tough QRM (or zero beating) might be worthwhile for you to switch in at times.  KL7CW
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KB1GMX

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Re: KX1 sidetone problem
« Reply #4 on: November 23, 2020, 09:10:29 AM »

It could also be that the audio system has a fault and is distorting the signal.
assuming its the off the air tone.

If its the keyed sidetone I believe that is a different problem.

Allison
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VE3WMB

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Re: KX1 sidetone problem
« Reply #5 on: November 27, 2020, 01:51:51 PM »

The sidetone's pitch doesn't sound clear to my ear. Achieving zero beat is therefore challenging. Does anyone else experience this? I read one post that said the sidetone is a square wave. Is that the problem I am hearing?

Is there a mod that adds some musicality to the sidetone?

I know there is a small circuit board kit that one can add that has an LED light up when one has zero beat. I bought one, but never built it.

I took a quick peek at the schematic and it seems that the sidetone is a slightly filtered square wave.  From what I can see there is a connection
from the MCU to the audio amp, after the TX mute switch, and it is in series with a 27pF C0G cap and a 1 M resistor. I don't know how much
filtering/smoothing such a simple R/C circuit provides, probably just enough to make it bit less raspy. 

For me I have always found that narrowing down the filter bandwidth on the KX1 a bit and tuning for a peak in volume always seemed to work ok.
I never try to match the pitch, at least not consciously.

Cheers

Michael VE3WMB

P.S. My only gripe with the KX1 is that because of the lower RX sensitivity on 20m you have to crank the volume up on that band.
Then when you go to TX the sidetone kills your ears if you are wearing sensitive earbuds. After while I learned to reduce the volume before TXing on 20m. ;-)
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