[Elecraft] Power Readout Discrepency

[Ron D'Eau Claire]

I've played with the 1N5711 RF detection circuits too. While they are
superior to the 1N34 germanium diode that has been commonly used as an =
RF
detector for many years, the 1N5711 is NOT absolutely flat across the HF
spectrum and their characteristics do vary somewhat from diode to diode. =


You got my curiosity up so I plugged my K2 into two external devices: an =
RF
ammeter and an external wattmeter. The ammeter uses a current sensing
transformer. It is a lot "flatter" in its response than the old =
thermocouple
ammeters.   The wattmeter is quite flat up to the vicinity of 500 MHz. =
They
both agreed to within a couple of hundred milliwatts.  With the K2 set =
for
10 watts out on the display, here's what my external meters indicated:

160 meters: 9.7 watts
 80 meters: 10.1 watts
 40 meters: 11.5 watts
 30 meters: 11.3 watts
 20 meters through 10 meters: 10.6 watts

If you have two meters spec'd at 10% accuracy such as the Oak Hills unit =
and
the internal meter in the K2, they may show a comparative error of up to =
20%
of course. It does get a little curious if, when using three =
instruments,
two agree closely and the third appears to be off by a large margin. But
that's not definitive if the total error is less than the sum of the
possible errors. =20

Wasn't it Murphy who decreed that all errors add in the most damaging =
(or
confusing) way possible?=20

Ron AC7AC
K2 # 1289


-----Original Message-----
My K2, #2636 has always had a large discrepancy in the displayed power =
vs
what I see on other, external wattmeters, including units from Oak Hills =
and
Diamond.  I know these are not lab quality devices, but I still think =
things
should agree a little better.  I talked to Eric about this yesterday at
Dayton.  I get the idea that non-linearities in the rf detector D9 could =
be
a factor.  Has anyone had any experience with this?  I'm thinking of
replacing D9 just to see if that's the problem.  Below are my =
K2-indicated
power levels for 10 watts out, measured through a Diamond wattmeter
connected to a commercial dummy load.  Bands progress from 160 through =
10
meters, respectively.  I see similar non-linearity at lower powers =
through
the WM-2 wattmeter.

8.2, 8.5, 8.8, 8.4, 6.2, 6.8, 8.6, 11.0, 11.0

I would appreciate any comments on this.  I've confirmed
that I have the correct diode at D9 and solder joints are
good.

Parker WD8JOL