K2 Power Control Question

[engineercm]

I'm becoming more active in QRP contesting and need to make sure that my
power is <5W.  I thought I was aligned ok until I put my LP100A into the
shack (what a wonderful instrument).  When Power Control = 5.0, the LP100A =
3.0.  Now, I want to be below 5.0, but not that low!  To reach LP100A = 5,
Power Control must be set at 7.5 (40m) and 8.5 (20m).  This is with the ATU
= Cal(P), which removes the matching circuits.  The dummy load is a MFJ-264;
the LP100A SWR = 1.13.

I'm okay with cranking Power Control to 8 to get 5w, but would prefer to
have the setting be closer to the acutal power out.  I've searched the
archives and can't find a similar problem.  I looks like there is a
component problem in the Power Control circuitry, but I'm not sure how to
find it.

I know there are lots of K2 owners out there and hope someone can provide
suggestions as to where to start.

72,

Clark WU4B
K2 #6011



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[Don Wilhelm]

Clark,

The "secret" is to properly balance and calibrate the KAT2 wattmeter.

If you do the balance with a dummy load that is truly a 50 ohm resistive
load ( a 1.13 SWR just does not "cut it"), then adjust the forward KAT2
pot to give you the same K2 display as indicated by the LP-100, your
power should track nicely.

Your K2 power output does depend on the correct calibration of the KAT2
wattmeter.

73,
Don W3FPR

On 12/17/2018 9:03 PM, engineercm wrote:
> I'm becoming more active in QRP contesting and need to make sure that my
> power is <5W.  I thought I was aligned ok until I put my LP100A into the
> shack (what a wonderful instrument).  When Power Control = 5.0, the LP100A =
> 3.0.  Now, I want to be below 5.0, but not that low!  To reach LP100A = 5,
> Power Control must be set at 7.5 (40m) and 8.5 (20m).  This is with the ATU
> = Cal(P), which removes the matching circuits.  The dummy load is a MFJ-264;
> the LP100A SWR = 1.13.
>
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[engineercm]

Ahhhh......

Thanks.  Forgot about the interaction of the ATU bridge and the Power
Control setting.

Measured R of MFJ unit = 57 Ohms.  Yuk.  Replaced it with my NORCAL load
which measured 49.5 ohms.  Now the LP100A shows SWR = 1.02.  Will
re-balance the bridge and report back.

BTW:  don't you ever sleep?

On Mon, Dec 17, 2018 at 9:27 PM Don Wilhelm <[hidden email]> wrote:

> Clark,
>
> The "secret" is to properly balance and calibrate the KAT2 wattmeter.
>
> If you do the balance with a dummy load that is truly a 50 ohm resistive
> load ( a 1.13 SWR just does not "cut it"), then adjust the forward KAT2
> pot to give you the same K2 display as indicated by the LP-100, your
> power should track nicely.
>
> Your K2 power output does depend on the correct calibration of the KAT2
> wattmeter.
>
> 73,
> Don W3FPR
>
> On 12/17/2018 9:03 PM, engineercm wrote:
> > I'm becoming more active in QRP contesting and need to make sure that my
> > power is <5W.  I thought I was aligned ok until I put my LP100A into the
> > shack (what a wonderful instrument).  When Power Control = 5.0, the
> LP100A =
> > 3.0.  Now, I want to be below 5.0, but not that low!  To reach LP100A =
> 5,
> > Power Control must be set at 7.5 (40m) and 8.5 (20m).  This is with the
> ATU
> > = Cal(P), which removes the matching circuits.  The dummy load is a
> MFJ-264;
> > the LP100A SWR = 1.13.
> >
>

--
72,

Clark, WU4B
QRPARCI #10815
SKCC #3892
NAQCC #5055
CWOPS #1869
Collins Collectors #AC90-12432
Southeastern DX Club <http://www.sedxc.org>
North Georgia QRP Club <http://www.nogaqrp.org>


*"It is vain to do with more what can be done with less."*
*Attributed to *William of Occam (1288 AD - 1348 AD)
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