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KX1 output power measurements

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Paul Huff

KX1 output power measurements

I was using my KX1 in the backyard yesterday to make some final adjustments and tests on a portable vertical that I will be using for field day. I noticed that when the KX1's antenna tuner indicated a high SWR it also indicated a much higher "output power." I assume that the reflected power throws off the measurement. Does anyone know what the maximum SWR is that will still provide a fairly accurate power reading?

Thanks and 73,
Paul - N8XMS
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Don Wilhelm-3

Re: KX1 output power measurements

Paul,

Yes, what you observed is true.

The KXAT1 wattmeter will indicate more power with increasing SWR *if^
the load impedance is higher than 50 ohms, but if it is lower than 50
ohms, the power indication will be lower. In ATU CAL mode, when the
power output is 4 watts into a 50 ohm load - if the load is 25 ohms pure
resistive, the power indication will typically be 2.2 to 2.5, and if the
load is 100 ohms pure resistive, the power indication will be typically
6.8 watts (the max value that will be displayed). I cannot say how the
indication varies with complex impedance loads, but I see the same thing
here with the precision 25 ohm and 100 ohm loads that I use when
adjusting for the SWR=2 point.

This phenomenon seems to be due to the absence of total power
calculation by the firmware. The difference of the squares between the
forward power and the reverse power must be calculated to indicate the
actual power to the antenna (with the phase angle properly included in
the calculation) - yes, the calculation seems to be incomplete in that
regard, but the relative indication is still informative.

After a tune cycle which reduces the SWR to somewhere near 1.0, the
power reading will be correct, but I have not measured just how close to
SWR=0 that must be.

That same characteristic is also true on the KAT1 wattmeter used in the
K1. and at the moment, I can't recall what happens with the K2 tuners.

73,
Don W3FPR

Paul Huff wrote:

> I was using my KX1 in the backyard yesterday to make some final adjustments and tests on a portable vertical that I will be using for field day. I noticed that when the KX1's antenna tuner indicated a high SWR it also indicated a much higher "output power." I assume that the reflected power throws off the measurement. Does anyone know what the maximum SWR is that will still provide a fairly accurate power reading?
>
> Thanks and 73,
> Paul - N8XMS
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>

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Don Wilhelm-3

Re: KX1 output power measurements

Sorry for the typo - the max power indication on the KX1 is 6.3 watts,
not 6.8.

73,
Don W3FPR

Don Wilhelm wrote:

> Paul,
>
> Yes, what you observed is true.
>
> The KXAT1 wattmeter will indicate more power with increasing SWR *if^
> the load impedance is higher than 50 ohms, but if it is lower than 50
> ohms, the power indication will be lower. In ATU CAL mode, when the
> power output is 4 watts into a 50 ohm load - if the load is 25 ohms pure
> resistive, the power indication will typically be 2.2 to 2.5, and if the
> load is 100 ohms pure resistive, the power indication will be typically
> 6.8 watts (the max value that will be displayed). I cannot say how the
> indication varies with complex impedance loads, but I see the same thing
> here with the precision 25 ohm and 100 ohm loads that I use when
> adjusting for the SWR=2 point.
>
> This phenomenon seems to be due to the absence of total power
> calculation by the firmware. The difference of the squares between the
> forward power and the reverse power must be calculated to indicate the
> actual power to the antenna (with the phase angle properly included in
> the calculation) - yes, the calculation seems to be incomplete in that
> regard, but the relative indication is still informative.
>
> After a tune cycle which reduces the SWR to somewhere near 1.0, the
> power reading will be correct, but I have not measured just how close to
> SWR=0 that must be.
>
> That same characteristic is also true on the KAT1 wattmeter used in the
> K1. and at the moment, I can't recall what happens with the K2 tuners.
>
> 73,
> Don W3FPR
>
> Paul Huff wrote:
>> I was using my KX1 in the backyard yesterday to make some final
>> adjustments and tests on a portable vertical that I will be using for
>> field day. I noticed that when the KX1's antenna tuner indicated a
>> high SWR it also indicated a much higher "output power." I assume
>> that the reflected power throws off the measurement. Does anyone know
>> what the maximum SWR is that will still provide a fairly accurate
>> power reading?
>> Thanks and 73,
>> Paul - N8XMS
>> _______________________________________________
>> Elecraft mailing list
>> Post to: [hidden email]
>> You must be a subscriber to post to the list.
>> Subscriber Info (Addr. Change, sub, unsub etc.):
>> http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/subscribers.htm
>> Elecraft web page: http://www.elecraft.com
>>
>>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>