KPA500 power fluctuations

[Poul Erik Karlshøj (PKA)-2]

For a while I have noticed that the KPA output indikations on both THE LEDs and the LCD display is fluctuating. The highest LED is flickering and the last two digits of the LCD are also fluctuating (hard to read, but at 500W it varies about 10W I think). It is the same at any power level from 20W to 500W. It is the same with the amp ON and STBY, so it seems to be a problem in the power monitoring circuit.

It is certain that the fault is in the KPA. I had another KPA connected to the K3 and its power indication was steady - just like they were on my own KPA until a few months ago. It is the same whether the amp is connected to a dummy load or an antenna and I dont hear anything unusual listening on a monitoring K2.

I did not yet have an opportunity to look at the power envelope on an instrument. So I dont know if the flickering is random like noise or not.

I thought that may be someone else on this list has seen this fault and might explain what's wrong.

/Poul-Erik
OZ4UN

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[Thomas Horsten]

Hi Poul-Erik,

It sure sounds like a fault in the KPA500 power measuring circuit in your
case, but is the output signal affected in any way? And does the SWR LED's
fluctuate/flicker as well? I had that problem and it turned out to be a bad
patch cable from the KPA500 to the KAT500. It would only happen above 100W
or so, and on certain bands/frequencies.

73, Thomas M0TRN / OV5T



On 20 June 2014 11:48, Poul Erik Karlshøj (PKA) <[hidden email]> wrote:

> For a while I have noticed that the KPA output indikations on both THE
> LEDs and the LCD display is fluctuating. The highest LED is flickering and
> the last two digits of the LCD are also fluctuating (hard to read, but at
> 500W it varies about 10W I think). It is the same at any power level from
> 20W to 500W. It is the same with the amp ON and STBY, so it seems to be a
> problem in the power monitoring circuit.
>
> It is certain that the fault is in the KPA. I had another KPA connected to
> the K3 and its power indication was steady - just like they were on my own
> KPA until a few months ago. It is the same whether the amp is connected to
> a dummy load or an antenna and I dont hear anything unusual listening on a
> monitoring K2.
>
> I did not yet have an opportunity to look at the power envelope on an
> instrument. So I dont know if the flickering is random like noise or not.
>
> I thought that may be someone else on this list has seen this fault and
> might explain what's wrong.
>
> /Poul-Erik
> OZ4UN
>
> Sendt fra min iPad
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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[Dan Maase AC6DM]

I've observed metering fluctuations as well.

Equipment:  K-line.
ALC off
Operating mode:  Amplifier output direct to dummy load or antenna -- same observed behavior with either load.
Constant power, e.g. CW
All cable verified as good.

1.  KPA500 LED Power Indication -- In standby or operate, the last power LED flickers.  In Standby, at any drive power, the last power LED flickers.  In Operate, at any drive power, the last power LED always flickers.  
2.  KPA500 SWR metering -- always stable
3.  KPA LCD Analog power metering -- In standby, the meter is stable; i.e., with 100 watts drive -- indicates 100 watts.  In operate, at any power level, the analog meter fluctuates.  The amount of the fluctuation is difficult to discern since it varies rapidly.
4.  Peak Hold -- when in Peak Hold mode, the last power LED's are stable, but occasionally in Operate, the next to last LED flickers.

K3 metering stable.

When monitoring the K3 or KPA power output on Elecraft W2, the power indication is stable.

Question:  Is this a KPA500 metering anomaly?  Or is this an indication of a power supply noise problem, e.g., power supply hum?  No one has complained of hum.  I did get one and only one comment from a discerning individual that there was audio break-up at peak modulation.

I've not yet rigged up a scope on the PS, pending comment from others.

Dan
AC6DM

[Dan Maase AC6DM]

Addendum:

KPA500 LCD voltage metering also fluctuates rapidly when in Operate mode and under load.  Nominal voltage 60 volts at 500 watts output.  Fluctuation amplitude cannot be discerned since variations are rapid.

Dan
AC6DM