[Elecraft] K2 RF Output...SOLVED

jerry jerry at tr2.com
Thu Aug 12 15:31:18 EDT 2021 

Well, that was easy.

    With the help of Don w3fpr, of course.

    Turns out that the internal wattmeter in the KPA100 was giving bad 
info to the
K2.  It was reporting about half the actual wattage.  A quick tweak of 
R26 ( and R27 to match ) fixed it up.

                   - Jerry KF6VB



On 2021-08-12 11:00, jerry wrote:
> 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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