Lower power output after master reset...

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Lower power output after master reset...

Steve Kallal
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

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Re: Lower power output after master reset (long)...

Don Wilhelm-3
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
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RE: Lower power output after master reset...

Brett gazdzinski-2
In reply to this post by Steve Kallal
 
One thing I noticed on my K2 is that the slightest
swr will fold back the power output a lot.

The basic K2 reads power output as voltage only at the
antenna output, and that is used to adjust the power
output of the radio.
Pushing the tune button would change the power output
a lot, as the rig reads the voltage and makes adjustments.

When you add the built in antenna tuner, that has an swr
reading circuit, so power is more accurate and stable I think.

I think there is an swr calibration procedure, and you
might also make sure the antenna tuner actually tuned down
to a 1.1 to 1 swr.

Brett
N2DTS



> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]] On Behalf Of Steve Kallal
> Sent: Monday, July 30, 2007 11:12 AM
> To: [hidden email]
> Subject: [Elecraft] Lower power output after master reset...
>
> 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
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft   
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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