[Elecraft] KAT2 power calibration

[Don Wilhelm]

Johnny,

Things are not always perfect, so you can expect some variation.
The 1N5711s in the KAT2 are not entirely frequency independent,  and the
detector in the LP100 is similarly frequency dependent. The exact results
will vary with the particular 1N5711 diode that is in your KAT2 and the
particular diode detector in your LP100.

OTOH, you have to believe something.  Take into consideration the potential
errors of everything in the calibration chain:
My previous emails with Larry have revealed that he uses an HP836A for his
reference - consider that the HP836A is good to 2% (that is optimistic) -
then, your LP100 may be good to 5% of the actual reading, and the KAT2 may
also be good to 5% of the actual reading, the total window for error is
12% - you said only that the KAT2 reading is higher than that of the LP100,
but you failed to say by how much.  I would expect that it should be well
within my optimistic error of 12% (1.2 watts at a 10 watt level).

This is a lesson in calibration practices - every potential error in the
calibration system must be accounted for.  If you want to obtain labratory
standard practice, the standard should be 10 times more accurate than the
device being calibrated.  I doubt you will find that level acceptable in any
wattmeters available today.  You may just have to be satisfied with some
reasonable discrepancy.  Alas, it is not a perfect world, especially not in
the wattmeter arena.

All in all, I have found that the KAT2 agrees with my 100 MHz 'scope (and
150 MHz probes) and and along woth my precision dummy loads I can achieve a
KAT2 calibration within 5% across all bands.  I believe the LP100 is rated
at 5% too.  So if you are no more than 10% different between the two, you
are doing pretty good.  That is a whole lot better than the 'run of mill'
amateur grade wattmeter which is speced at 20% of full scale.

Your output power 'tweaking' is not related to the power output reported by
the KAT2, but I am glad that you achieved good results by using Gary's
advice.  If you have an antenna analyzer, you can 'tweak' the LPF for the
best SWR across the bands and obtain even better results than those obtained
by 'tweaking' for maximun power output.  If you attempt that, be certain
that you terminate the LPF in 50 ohms - which means removing the W1 jumper
and inserting a 50 ohm load (this can be done easily at the K160RX header if
you have that option installed).

73,
Don W3FPR

> -----Original Message-----
>
> I have recently got Larry¡¯s LP100 digital wattmeter (factory
> calibrated).
> I therefore used it to re-do the power calibration of KAT2 with
> K2.  I did
> it according to the manual by adjusting R1 to get a matched
> reading between
> K2 and LP100.  The K2 was set at 7100khz.
>
> However, I noted the following:
>
> For 17, 15, 12, 10m ¨C the power output reading in K2 is higher than that
> of LP100;
> For 80, 160m ¨C the power output reading in K2 is lower than that of LP100
>
> Is this a normal observation ????
>
> I also take this chance to realign the output power of my K2
> especially the
> 10m band.  Gary¡¯s advice in the email resource page does really work.  I
> got higher output on 10m by expanding or / and compressing L21 & L22 and
> T2.  I also did the same for T1 and got slightly power after the previous
> step.
>
> TNX & 73
>
> Johnny Siu VR2XMC
>
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