[Elecraft] KPA100 SWR bridge adjustment 160m & 80m

[Koert Wilmink]

Dear Don,

Just did check the dummyload with an MFJ analyzer and is working fine on
160m and higher.

73 Koert PA1KW

Koert Wilmink wrote:
> Dear Don,
>
> Thanks for your support!! there is a deep and sharp null for all bands
> except 80 &160m, cannot get lower than 1.3 for 80 and 1.8 for 160, I did
> check the core and it is the large dark gray core. I also removed T4 and
> did check the solder connections. No difference in results.
> Maybe asking Elecraft for a new FT50-43 core? I also will ask my
> colleague amateurs for another dummyload, just to be 100% sure. The
> current one I'm using is from Annecke and the freq it is capable of
> handling is 2 Ghz.
> 73 Koert PA1KW
>
>
> Don Wilhelm wrote:
>   
>> Koert,
>>
>> The absolute minimum voltage found in the C1 null (as observed at TP4)
>> is not as important as the depth of the null.
>>
>> If you cannot achieve a deep and rather sharp null, there is something
>> wrong with either T4 and its associated components or with your dummy
>> load.  The actual voltage at the null will depend on the power level
>> used.
>>
>> Assuming your dummy load is good (you can check it with an antenna
>> analyzer), you should see a 1.0:1 SWR on all bands.
>>
>> Since you indicate a higher SWR on the low frequency bands, that
>> suggests that T4 does not have adequate inductance for those bands. 
>> Check that you have used the correct core for T4 - it should be one of
>> the gray (ferrite) cores and not one of the black (powdered iron)
>> cores.  Be certain that T4 has well stripped leads and is properly
>> soldered.  If you observe toroid solder connections that look a bit
>> like volcanos, that lead was not well stripped - a good solder
>> connection will look like a mountain with concave sides - if it has a
>> convex shape, too much solder was applied and that fact can mask a
>> poor solder connection - wick away the excess solder and resolder
>> properly.
>>
>> 73,
>> Don W3FPR
>>
>> Koert Wilmink wrote:
>>     
>>> Dear all,
>>>
>>> Please find my emails to Elecraft support below. Is there maybe
>>> somebody with additional tips?
>>>
>>> Thanks!!
>>>
>>> 73 Koert PA1KW
>>>
>>>
>>>
>>> -----------------------------------------------------
>>> Hi Gary,
>>>
>>> Sorry for my late response, but I had not the opportunity to work on
>>> this earlier. I moved houses and that took longer than expected.
>>>
>>> I did check the HV bias and that is 135volts. The diodes are ok and the
>>> voltage on TP4 2mV on receive and 240mv on transmit (tune).
>>> I did connect a good dummyload close to the KPA100.
>>> I did the re-adjustment of the SWR bridge but this provided me not the
>>> required results. The best results with adjusting C1 on 5 Watts is:
>>>
>>> 160m 1.8-1
>>> 80m 1.3-1
>>> 40m 1.0-1
>>> 30m 1.0-1
>>> 20m 1.0-1
>>> 18m   1.0-1
>>> 15m 1.0-1
>>> 12m  1.0-1
>>> 10m 1.0-1
>>>
>>> Please help......
>>>
>>> Best regards and 73,
>>>
>>> Koert Wilmink
>>> PA1KW
>>>
>>>  
>>>       
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