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KPA100/KAT100 trouble

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Chris Kantarjiev K6DBG

KPA100/KAT100 trouble

I may be having my first run-in with lightning damage.

A thunderstorm rolled through the SF Bay Area last night. I didn't
disconnect my antennas until I *saw* the first lightning flash.

Oops, I think.

I turned on the radio later in the evening, and was getting very
high SWR indications on the KAT100, and HiCur on the K2. Hitting
TUNE caused a lot of clicking and clacking, and eventual tune to
about 1.5:1, but SWR was still high on transmit - and the indicated
power on the bargraph was lower than dialed in. This is on both
antennas - a vertical and OCF dipole - both more or less resonant.

I turned off the rig and called it a night.

This morning I pulled out my LP200 dummy load/power meter. The ATU
tunes it to 1.1:1. Power out does not change appreciably
in response to the POWER knob - if set for any value less than 10W,
the power is about 4W; if set for values about 10W (PA on), power
out is always about 30W. In neither case is the LED indication on
the K2 correct.

I also notice that the SWR LEDs no longer display anything when the
power is set below 10W, but indicate as expected when POWER is
above 10W.

If I put the ATU into CAL mode, which I understand removes all the
LC network, the SWR LEDs indicate 5:1 (all on), and the power out
is higher, but still doesn't respond to the POWER knob: 10W on
LOW mode, about 90W in HIGH mode.

Connected to the K2/KAT2 (with the serial cable disconnected) the K2
operates as expected (once I remember to turn the ATU back to AUTO :-)

I'm not even sure where to begin looking, but it certainly seems
that the SWR bridge might be malfunctioning.

Help?

Thanks!

73 de chris K6DBG
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Don Wilhelm-4

Re: KPA100/KAT100 trouble

Chris,

As your first step, you need to obtain some 1N5711 diodes - obtain 5 of
them if you have to order any.

First remove the KPA100 and check the base K2 into a good dummy load.
Do you have good power control over the entire range? If yes, the base
K2 is working, but if no, replace RF Board D9 and re-check.

Once you have verified that the base K2 can control the power output,
add the KPA100 - operate into a dummy load (no antennas please because
there are too many variables to deal with). If the K2 with KPA100
properly controls power and displays a 1:1 SWR, then you will have 2
more extra diodes. OTOH, if the KPA100 produces full power output no
matter where the power knob is set, then replace D16 and D17 in the
KPA100. The K2 with KPA100 should now properly control power output.

Lastly, add the KAT100, but set the ATU menu to CAL and connect the
dummy load to the KAT100. If all works well, you have extra diodes, but
if all is not well, then replace D1 and D2 in the KAT100.

After all is working fine into a dummy load, then you can connect an
antenna and try it out - you should find normal behavior.

OK, this has been simplistic and considers only that the lightning
zapped the wattmeter diodes. This is usually the only consequence, but
if at any point, normal behavior is not restored after replacing the
diodes, there is some other problem that must be investigated before
attempting to proceed any further with the testing.

73,
Don W3FPR

Chris Kantarjiev wrote:

> I may be having my first run-in with lightning damage.
>
> A thunderstorm rolled through the SF Bay Area last night. I didn't
> disconnect my antennas until I *saw* the first lightning flash.
>
> Oops, I think.
>
> I turned on the radio later in the evening, and was getting very
> high SWR indications on the KAT100, and HiCur on the K2. Hitting
> TUNE caused a lot of clicking and clacking, and eventual tune to
> about 1.5:1, but SWR was still high on transmit - and the indicated
> power on the bargraph was lower than dialed in. This is on both
> antennas - a vertical and OCF dipole - both more or less resonant.
>
> I turned off the rig and called it a night.
>
> This morning I pulled out my LP200 dummy load/power meter. The ATU
> tunes it to 1.1:1. Power out does not change appreciably
> in response to the POWER knob - if set for any value less than 10W,
> the power is about 4W; if set for values about 10W (PA on), power
> out is always about 30W. In neither case is the LED indication on
> the K2 correct.
>
> I also notice that the SWR LEDs no longer display anything when the
> power is set below 10W, but indicate as expected when POWER is
> above 10W.
>
>

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Chris Kantarjiev K6DBG

Re: KPA100/KAT100 trouble

Don,

It's taken me several weeks to get to this, but tonight was the night. I had
tested and determined that the base K2 was fine, but neither the KPA nor KAT
controlled power correctly. The parts folks had sent me diodes.

Boy, what a nuisance these are to replace! Julius N2WN had suggested putting the
KPA's diodes on the underside of the board, where they are easier to get at, and
I followed that advice. For the KAT, there's just no good way to get at the
backside of the board w/o removing all the connectors. I used a stainless dental
pick to clean out the holes from the front, and soldered from that side, too.

Power control works great now. Both bridges seem to want to be recalibrated -
the max output is about 75W, even when I have 100+ dialed in. I didn't do the
original calibration on these, so I'm not certain of how close they were ... and
I guess I'm not sure that I measured for full power out when I bought them.

I suspect that it's a calibration issue, because output is low across the entire
HIGH range. The bargraph is showing about the right number of bars for the POWER
setting.

Or is there some other problem I should be looking for that might cause this?

Thanks again.

73 de chris K6DBG

Don Wilhelm wrote:

> Chris,
>
> As your first step, you need to obtain some 1N5711 diodes - obtain 5 of
> them if you have to order any.
>
> First remove the KPA100 and check the base K2 into a good dummy load.
> Do you have good power control over the entire range? If yes, the base
> K2 is working, but if no, replace RF Board D9 and re-check.
>
> Once you have verified that the base K2 can control the power output,
> add the KPA100 - operate into a dummy load (no antennas please because
> there are too many variables to deal with). If the K2 with KPA100
> properly controls power and displays a 1:1 SWR, then you will have 2
> more extra diodes. OTOH, if the KPA100 produces full power output no
> matter where the power knob is set, then replace D16 and D17 in the
> KPA100. The K2 with KPA100 should now properly control power output.
>
> Lastly, add the KAT100, but set the ATU menu to CAL and connect the
> dummy load to the KAT100. If all works well, you have extra diodes, but
> if all is not well, then replace D1 and D2 in the KAT100.
>
> After all is working fine into a dummy load, then you can connect an
> antenna and try it out - you should find normal behavior.
>
> OK, this has been simplistic and considers only that the lightning
> zapped the wattmeter diodes. This is usually the only consequence, but
> if at any point, normal behavior is not restored after replacing the
> diodes, there is some other problem that must be investigated before
> attempting to proceed any further with the testing.
>
> 73,
> Don W3FPR
>
> Chris Kantarjiev wrote:
>
>> I may be having my first run-in with lightning damage.
>>
>> A thunderstorm rolled through the SF Bay Area last night. I didn't
>> disconnect my antennas until I *saw* the first lightning flash.
>> Oops, I think.
>>
>> I turned on the radio later in the evening, and was getting very
>> high SWR indications on the KAT100, and HiCur on the K2. Hitting
>> TUNE caused a lot of clicking and clacking, and eventual tune to
>> about 1.5:1, but SWR was still high on transmit - and the indicated
>> power on the bargraph was lower than dialed in. This is on both
>> antennas - a vertical and OCF dipole - both more or less resonant.
>>
>> I turned off the rig and called it a night.
>>
>> This morning I pulled out my LP200 dummy load/power meter. The ATU
>> tunes it to 1.1:1. Power out does not change appreciably
>> in response to the POWER knob - if set for any value less than 10W,
>> the power is about 4W; if set for values about 10W (PA on), power out
>> is always about 30W. In neither case is the LED indication on
>> the K2 correct.
>>
>> I also notice that the SWR LEDs no longer display anything when the
>> power is set below 10W, but indicate as expected when POWER is
>> above 10W.
>>
>>
>
>
>

Don Wilhelm-4

Re: KPA100/KAT100 trouble

Chris,

I am pleased to learn that you have had success with the diode
replacement. They are a bit difficult to reach, and there is no reason
they cannot be placed on the bottom of the board as you have done.
Do correct the power supply situation before drawing any further
conclusions about maximum power output, but you can calibrate the
wattmeters even with your limited current battery.

You can calibrate the wattmeter in the KPA100 and the KAT100 at 10 watts
and that typically provides good results over the entire range. The
KAT100 manual gives you voltage measurements to do that calibration and
will normally yield quite acceptable calibration results - just follow
the manual instructions.

Actually doing the KPA100 wattmeter calibration at 10 watts will provide
good accuracy over the entire range too (there is scaling at high power
built into the KPA100). Power only the base K2 and the power control
steps will provide more resolution during the calibration, and if you
have an accurate dummy load, you can read the RF voltage across the
dummy load with an RF Probe and calculate the actual power.

The K2 LED bargraph does not have sufficient resolution to measure the
actual power output - if you have the Elecraft DL1, you can use it with
the built-in detector to determine the actual power, but lacking that
tool, use an RF Probe and a good 50 ohm non-reactive dummy load to
calculate the power - most RF Probes will withstand RF voltages across a
50 ohm load for up to about 18 watts.

73,
Don W3FPR

Christopher A. Kantarjiev wrote:

> Don,
>
> It's taken me several weeks to get to this, but tonight was the night.
> I had tested and determined that the base K2 was fine, but neither the
> KPA nor KAT controlled power correctly. The parts folks had sent me
> diodes.
>
> Boy, what a nuisance these are to replace! Julius N2WN had suggested
> putting the KPA's diodes on the underside of the board, where they are
> easier to get at, and I followed that advice. For the KAT, there's
> just no good way to get at the backside of the board w/o removing all
> the connectors. I used a stainless dental pick to clean out the holes
> from the front, and soldered from that side, too.
>
> Power control works great now. Both bridges seem to want to be
> recalibrated - the max output is about 75W, even when I have 100+
> dialed in. I didn't do the original calibration on these, so I'm not
> certain of how close they were ... and I guess I'm not sure that I
> measured for full power out when I bought them.
>