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

[Koert Wilmink]

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
>>
>>  
>