[Elecraft] Lower power output after master reset (long)...

[Don Wilhelm]

Steve,

There is nothing that you did which would alter the power output.  There 
are no settings which control the maximum output, other than the CAL CUR 
setting which defaults to 2.50 Amps and should be adequate for the QRP 
K2 - the indication that CAL CUR may be reducing the maximum power wold 
become apparent because a HI CUR message would be presented on the display.

If the trimer pots on the KAT2 were moved, that would provide an 
explanation.  Set the ATU menu to CALP, attach a good dummy load and see 
what the power indication is under those conditions.  If you want to 
assure yourself that the KAT2 indication is accurate, go through the 
procedure I have detailed below. (do that before assuming there is a 
problem with the K2 or the KAT2).

Are you using a good power supply which produces 13.8 volts, and do you 
have a good power cable of adequate gauge between the power supply and 
the K2?  I prefer 16g or larger wire to minimize the voltage drop.  tap 
the DISPLAY button and then do a TUNE while observing how much the 
voltage drops during transmit - you may be surprised.

If you have adequate voltage to the K2 during transmit and the power 
indication is still low, you should check to see whether the problem is 
in the base K2 or the KAT2 forward power alignment.  Remove the KAT2 and 
connect a known good 50 ohm resistive dummy load to the K2 BNC 
connector.  It is wise to check the dummy load with an antenna analyzer 
and operate near the frequencies where it is really a 50 ohm 
non-reactive load.  With the KAT2 disconnected, the 'power detector' is 
a simple diode detector and will be as accurate as your dummy load.  See 
what the maximum power is with that combination - that checks the K2 
power output capability.

Next attach the KAT2, and set the ATU parameter to CALP.  Attach the 
known good dummy load to the ANT1 jack (make sure the K2 has ANT1 
selected).  Do a TUNE while monitoring the DC voltage at the hot end of 
KAT2 R2, and using an insulated screwdriver, adjust C55 for the smallest 
voltage that you can produce - the KAT2 wattmeter bridge is now balanced.

Next you will need something to measure the actual power into the dummy 
load - a known accurate wattmeter (but some of them have errors 
approaching 20% of the full scale reading - that is 20 watts on a 100 
watt scale!), or a calibrated oscilloscope and good 10x probe, or an RF 
probe and your DMM.  If you have an accurate wattmeter, it is easy - 
just adjust KAT2 R1 until the K2 display indicates the same power as 
your wattmeter.  If you use the 'scope, connect it across the dummy load 
(a TEE adapter will give you access if there is no other way) and 
measure the peak to peak RF voltage on the 'scope - use the formula 
V^2/400 (where V is the peak to peak voltage) to calculate the power - 
adjust R1 until the calculated power and the K2 display agree.  If you 
are using an RF probe, you must know if it reads in RMS voltage or peak 
voltage.  Most RF Probes have the diode connected between the ground lug 
and the 'hot' side of the probe (like that shown in the K2 manual) and 
will read RMS voltage - if you have a probe like that, the formula for 
power is V^2/50 where V is the RMS value of the RF voltage.  If your RF 
probe uses a series diode, it will indicate the zero to peak voltage of 
the RF wave and you can calculate the power as V^2/100 where V is the 
zero to peak RF voltage.  All the above formulas assume a 50 ohm dummy 
load - vary from that and you will have inaccurate results.   The peak 
reading RF Probe does have the voltage drop of the diode to consider, 
but can be ignored (because it is small) for powers above 2 watts or so.

The Elecraft DL1 is another alternative as a good dummy load because it 
not only is a good 50 ohm load, but contains a peak reading diode 
detector as well - so if you have the DL1, you can compute the actaul 
power by using the formula in the manual or using a graph.

Once you calibrate the wattmeter in the KAT2, then you will know its 
accuracy and can properly address whether or not there is a low power 
output from your K2.

73,
Don W3FPR

Steve Kallal wrote:
> Hi,
>  
> I managed to fix my K2 after an intermittent on the Control Board appeared.
> In the process I did a master reset hoping somehow that would fix my
> problem. Now that my K2 is operational again, I've lost some of my power
> output. It is almost certainly a calibration or setting issue.
>  
> I didn't build this K2 nor any other. So I don't know my way around the rig.
> It also has the KAT2 option, which probably also lost some settings.
>  
> My power used to peak at 15 watts on 40 meters. Now it is lucky to get 10
> watts. Otherwise the K2 seems just fine.
>  
> Can someone point me to right part of the manual to make the necessary
> adjustments. My K2 is serial number 2289. It has the mods for the conversion
> of Revision B and the 2.04p firmware. The KAT2 firmware is 1.09, at least
> that is the second # showing in the version display.
>  
> 73,
> 
> Steve N6VL