K2 power output

[Slater Tubman]

I have noticed an irregularity on my K2 output.

When setting the power level a 2 watts, and then using the ATU I get a
reading on my SWR/power meter in the line of 4 watts.   Setting power
on the K2 to 3 watts, I get 4 watts on the in line meter. I thought the
meter might be faulty, so replaced it with another with the same
result.  And the ATU gives me a reading of, say 1.3:1, whereas the
SWR/power unit shows 3:1.

Do I have a problem.  If so, how do you suggest I address it?

Thanks
Slater VE5OA
SN 4519

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[Ron D'Eau Claire-2]

Slater, VE5OA wrote:

I have noticed an irregularity on my K2 output.

When setting the power level a 2 watts, and then using the ATU I get a
reading on my SWR/power meter in the line of 4 watts.   Setting power
on the K2 to 3 watts, I get 4 watts on the in line meter. I thought the
meter might be faulty, so replaced it with another with the same
result.  And the ATU gives me a reading of, say 1.3:1, whereas the
SWR/power unit shows 3:1.

Do I have a problem.  If so, how do you suggest I address it?

----------------
To compare your ATU internal SWR metering with an external meter, the
external meter must be connected directly to the ATU with a short 50 ohm
cable. If you are using an ATU, it must be attached after the external
meter. You need a short cable because any residual SWR on the line will
cause variations in the readings on a meter only a few inches from the rig,
depending upon the frequency where you are running the tests. Even if the
SWR meter shows 1:1, there may be enough of a residual mismatch to cause
significant error. SWR bridges are fine for showing that the impedance
presented to a rig is close enough to 50 ohms resistive for efficient
operation, but they are not precision instruments.  

Ideally, connect your external meter directly to the K2 using a suitable
coaxial adapter.  Then your SWR and power readings should be similar,
although there are usually some variations. Most power meters Hams use -
even the over US$100 variety - are seldom closer than 20%. That is, a rig
producing 5 watts may show 4 watts on one meter and 6 watts on another.

>From your notes, it sounded like you might have one SWR meter connected
between the ATU and antenna. If so you cannot get meaningful readings that
way. The reason for the ATU is to "tune out" reactance in the transmission
line and convert the resulting resistive impedance to 50 ohms to provide the
correct load the transmitter. The ATU has no effect on the SWR or impedance
of the antenna connected to it. If you put an SWR meter in the circuit
between the antenna and tuner it will be seeing impedances it was not
designed for and the readings will be very inaccurate.  

Ron AC7AC


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[Don Wilhelm-3]

Slater,

You likely do not have a problem.  Take away the antenna, in-line SWR meter,
and the ATU - and substitute a good 50 ohm dummy load.  Be certain it is 50
ohms resistive and has no capacitive or inductive component at the frequency
you want to do your testing (you can measure it with an antenna analyzer).

Use an RF Probe to measure the RF across the dummy load and use the formula
V^2 divided by R to calculate the power present and compare that with the
indication shown on the K2.

The RF Probe will be much more accurate than most wattmeters - but the
condition is that you must know th eimpedance of the load accurately.
Wattmeters can be off by as much as 20% of the full scale reading, and when
using a 200 watt scale, that is 40 watts!  Some are better, but many are
not - if you need validation of that, check out the accuracy reports in the
ARRL lab tests.

BTW, the basic K2 uses an RF Probe type measuring device to determine power
output, and is usually quite accurate as long as the load on the antenna
jack is 50 ohms resistive.  With other loads, the power indication will not
be accurate.  The KAT2, KPA100 and KAT100 do contain wattmeters reather than
the RF Probe, but they must be calibrated accurately if good readings are to
be expected (the dummy load and RF Probe method I mentioned above is good
for achieving good calibration).

73,
Don W3FPR

> -----Original Message-----
>
> I have noticed an irregularity on my K2 output.
>
> When setting the power level a 2 watts, and then using the ATU I get a
> reading on my SWR/power meter in the line of 4 watts.   Setting power
> on the K2 to 3 watts, I get 4 watts on the in line meter. I thought the
> meter might be faulty, so replaced it with another with the same
> result.  And the ATU gives me a reading of, say 1.3:1, whereas the
> SWR/power unit shows 3:1.
>
> Do I have a problem.  If so, how do you suggest I address it?
>
> Thanks
> Slater VE5OA
> SN 4519
>
>

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