KX1 ATU low power indication

[Frank R. Oppedijk]

Hi all,

Does anyone have any idea about the possible cause of the low power
reading by the KX1 ATU?

Thanks,

Frank

>Hi,
>
>After having been off the air for about a year (moving house; other
>interests) I have recently fired up my KX1 again. When tuning up a
>random length of wire, I noticed that the output power indicated by the
>KX1 ATU was only 0.4 to 0.5 Watts (while SWR was good: 1:1.0 to 1:1.1).
>I attached a 50 ohm dummy load and hooked up my oscilloscope and saw a
>nice 24V peak-to-peak voltage on key down. That's 1.4 Watts and IIRC not
>bad for a battery-powered KX1 (battery voltage indicated by the KX1:
>8.5V on receive, 8.4V on transmit).
>
>Why then the low power indication by the ATU?
>
>I have already taken the unit apart and have resoldered all solder
>joints on the ATU PCB, but to no avail. Does anyone have any ideas?
>
>Thanks in advance,
>
>73 de PA4N

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[Don Wilhelm-3]

Frank,

Yes, I have several ideas:

Check it first on a 50 ohm dummy load to see if the power output as measured
with your 'scope (or RF Probe) agrees with that displayed by the KX1.

Your antenna is connected to the output of the tuner, and the displayed SWR
is read at the input of the tuner.  What that means is the SWR looking into
the antenna itself can be a high SWR, but the tuner action matches it and
the SWR at the input to the tuner will be 1 (or close enough).  Since the
antenna itself may have a high impedance at the tuner output, the RF voltage
at that point by itself is meaningless for computing the power unless either
the RF current at that same point or the antenna feedpoint impedance is
known and used in the power computation.

After doing the check with a dummy load,and if it was indicating correctly
before, and now is found to be incorrect, look for a bad diode (1N5711) in
the wattmeter section of the KXAT1.  Then once you know the diodes are good,
readjust the balance capacitor and Forward and Reflected trimmer pots as
indicated in the KXAT1 manual.

If you find low power when operating into a 50 ohm dummy load, you should
look at the KX1 rather than the KXAT1 for the problem.

73,
Don W3FPR

> -----Original Message-----
>
> Hi all,
>
> Does anyone have any idea about the possible cause of the low power
> reading by the KX1 ATU?
>
> Thanks,
>
> Frank
>
> >Hi,
> >
> >After having been off the air for about a year (moving house; other
> >interests) I have recently fired up my KX1 again. When tuning up a
> >random length of wire, I noticed that the output power indicated by the
> >KX1 ATU was only 0.4 to 0.5 Watts (while SWR was good: 1:1.0 to 1:1.1).
> >I attached a 50 ohm dummy load and hooked up my oscilloscope and saw a
> >nice 24V peak-to-peak voltage on key down. That's 1.4 Watts and IIRC not
> >bad for a battery-powered KX1 (battery voltage indicated by the KX1:
> >8.5V on receive, 8.4V on transmit).
> >
> >Why then the low power indication by the ATU?
> >
> >I have already taken the unit apart and have resoldered all solder
> >joints on the ATU PCB, but to no avail. Does anyone have any ideas?
> >
> >Thanks in advance,
> >
> >73 de PA4N
>
>

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