[Elecraft] K3 RF Power Meter Accuracy

[Ron D'Eau Claire]

Jim, there are a number of things that can account for the discrepancy:

1) The K3 bargraph registers in 10 watt steps so it's difficult to
interpolate the 25 watt level. 

2) An SWR report of 1:1 into an antenna does not mean the load is the 50
ohms non-reactive the power meter expects. It's close, but not close enough
for a power meter calibration. You need a precision dummy load to compare
the power reports. 

3) Unless you are spending thousands and thousands of dollars on power
measuring equipment (including a precision dummy load), an error or 5% or
more is considered extremely accurate. Ten percent or greater is common. 

73, Ron AC7AC


-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Jim Bennett

I've been using my K3 #4359 now for several years w/o any issues. Just this
past week I acquired an LDG AT-600ProII auto tuner and the matching M-600
analog meter. I calibrated the M-600 per the instructions. What I'm seeing
is that the M-600 meter is showing me higher RF output than the K3's bar
graph on most bands. As an example, after setting the KAT3 to Bypass, using
the AT-600 to bring an antenna to a match (close to 1:1) with 5 watts out of
the K3, I turn the K3 power output to 25 watts. A key-down on the K3 shows
25 watts on the K3 bar graph, but the M-600 tells me that the power is about
39-40 watts. It is like this on nearly all the bands, 160-10 meters. On 6
meters, the M-600 reads about 20% LOWER than the K3.

I sent an email to LDG and asked them what's up - which is correct - the K3,
or the LDG unit? Their response is that the K3 most likely is incorrect, as
they calibrate their equipment with an Alpha 4500. That's a tad of an
expensive meter, to say the least. Are the LDG folks tweaking me on this, or
is that M-600 really more accurate than the RF bar graph on the K3?

Jim / W6JHB
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