[Elecraft] K2 RF Output

[jerry]

So - I figured - if something on the KPA100 is drawing excess current, 
and not
really doing anything with it, it must be making heat, right?

    I powered up the radio through the barrel connector, left the KPA100 
connected,
set it to "tune" at minimum power and just left it for a while.  Then 
felt around.
Then poked around with an infrared thermometer.

    Zilch.  Nothing anywhere is getting hot to trot.  Nor can I find any 
hot spots
on the heat sink.

                  - Jerry KF6VB


On 2021-08-12 10:22, jerry wrote:
> On 2021-08-08 09:49, Don Wilhelm wrote:
>> Jerry,
>> 
>> Replace diodes D16 and D17 in the KPA100 wattmeter, and things should
>> settle down.
> 
> *** The diodes came in from Mouser yesterday, and I replaced them.  
> Things
> are still not right.  I did get a good adjustment on C1, and it now 
> reads 1 to 1
> on all bands.
> 
>    HOWEVER, it still will not give full power. It fails with "HiCUR".
> 
>   If the KPA100 is installed but not powered up ( power from the
> barrel connector ),
> it gets to about 8W then fails "HiCUR".
> 
>   If the KPA100 is installed AND powered up AND enabled via the menu:
>    on 40M, it gets to a bit over 80W, then says "HiCUR".
>    on 20M it gets to about 65W, then "HiCUR"
> 
>   If I uninstall the KP100 completely, the radio gives full power - 
> 15.3W on
> 20M, 16.7W on 40M.
> 
>   Very mystifying.  I made up a cord to connect the barrel connector
> to my lab supply.
> Interesting results:  with the KPA100 connected but power through the
> barrel, the radio
> simply does draw enough current to shut it down with "HiCUR" at 8W.
> It shuts down at
> EXACTLY 3.5A measured by the power supply.
> 
>   With the KPA100 entirely disconnected, the radio makes 16W on 40M at 
> 3.15A.
> 
>   So my conclusion is that something in the KPA100 is drawing excess
> current, in transmit mode, even though the KPA100 is mostly not
> operating.
> 
>    In "tune" with the power all the way down, and the KPA100
> connected, the radio draws
> 750mA through the barrel connector.
> 
>    In "tune" with the power all the way down, and the KPA100
> DISCONNECTED, the radio
> draws 440mA through the barrel connector.
> 
>                  - Jerry KF6VB
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
>> If you attempted to adjust KPA100 C1 while this condition was present,
>> balance the wattmeter again, it will change with good diodes
>> installed.
>> The diodes are 1N5711 type.
>> 
>> That wattmeter is still used as long as the KPA100 is installed on the
>> base K2 - reducing the power to less than 12 watts does not take it
>> out of line.
>> 
>> CAL CUR should be set at 3.5 amperes with the KPA100 installed. That
>> (and the current display) is the current drawn by only the base K2,
>> and not to the KPA100.
>> 
>> 73,
>> Don W3FPR
>> 
>> On 8/8/2021 12:24 PM, jerry wrote:
>>> All,
>>> 
>>>   My new QRO K2 behaves a little strangely...
>>> 
>>> On Tune - it makes 108W on 40M, very nice.
>>> 
>>> But on 20M it behaves strangely.  It won't make more than 20W or so, 
>>> complains about high SWR. Even though my Heathkit HM-102 
>>> SWR/Wattmeter says the SWR is zilch.
>>> 
>>> So I moved it to a dummy load.  As I turn the power up, it makes up 
>>> to about 80W, and then says "Hi CURR".  And it claims that the dummy 
>>> load ( an 800W "Florida RF" resistor bolted to a large heatsink ) is 
>>> 1.6 to 1, which is totally bogus.
>>> 
>>> OK, there's a null trimmer for the SWR bridge.  I got it down to 
>>> 1-to-1 SWR on 20M.  It degrades on higher bands though - up to 1.5 to 
>>> 1 on 10M.
>>> 
>>> Now, 20M gives me a max of 45W - above that it complains "HI CUR".  
>>> It's doing that on all bands.  With the PA off via menu, I get a 
>>> maximum of about 8.5W before getting the "HI CUR" message. I tried 
>>> setting the current up a little bit on the CAL CUR menu, but no real 
>>> difference.
>>> 
>>>   With a clamp-on DC ammeter ( which I don't trust THAT much ) I see 
>>> 340mA on receive,
>>> and just about 3.6A when the display goes "HI CUR".  This is with the 
>>> PA turned off.  The
>>> display shows 7W just before this happens.  Hmm, 13.8V times 3.5A 
>>> means 48.3W DC input.  Seems a little excessive.
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