[Elecraft] KPA 100 Low power on 160M

[Andrew Lenton (Linux account)]

Hi Don,

Just to tie the ribbons, I completed the KPA 100 up grade, blue cores
ect, and it made no difference, so I went back to basics, "what could
cause a poor return loss on 160 only into the KPA 100?"  I checked the
following:

C86,  C67, D11, R2,1 R22, C66, C60, C61, C62, C63 and R9 The fault was
traced to D11. although it measured OK and the volt drop when forward
biased was reasonable 0.65V, it did not like 160M and gave a poor
reflection to the K2 ( high current warning). I had replaced it before
to try and cure this fault, which threw me, however, the current
replacement is from a different manufacture!! so maybe not all 1N4007's
are the same!

Now I have brought the KPA up to reversion E the radio seems a lot more
stable, I am currently adding the 60M and transverter board. Thanks for
all your words of wisdom

73 and Merry Christmas

Andrew & Sue (M3UUG)


On Sun, 2008-10-26 at 16:41 +0000, Andrew Lenton (Linux account) wrote:

> 
> Hi Don,
> 
> Ah very good point this rules out the low pass filter on the KPA 100,
> as low  power is OK. I only have this problem on 160, as 80 to 10 are
> fine
> 
> Th High current only show up on 160 M, the display on the K2 reads the
> same on the external watt meter Bird through line. SO! symptoms below
> are:
> 
> 
> 
>         1 Power on display matches Watt meter from 160 to 10 ( all be
>         it 160 is 60 Watts Max)
>         2 Power from 80 to 10 max 111 Watts on display and meter, no
>         high current warning
>         3, Power after 60 watts on 160 I get high current warning
>         4, I did not disturbed  R 26 it was covered by metal plate
>         when I removed the KPA100 to make way for the DSP, and the
>         setting of R26 would also affect other bands
>         
>         The Bird meter was calibrated this year with all its elements,
>         also I have more than one Watt meter, all say the same low
>         power on 160 and high current
>         
>         Something must have been disturbed somewhere!! I guess?
>         
>         73's
>         
>         Andrew
>         
> 
> 
> On Sun, 2008-10-26 at 10:43 -0400, Don Wilhelm wrote: 
> 
> > Andrew,
> > 
> > If the KPA100 low pass filter were a problem it would misbehave at both 
> > the low and high power ranges because it is always in the circuit with 
> > the KPA100 connected.
> > 
> > A "Hi Cur" message means the *base K2* is drawing current in excess of 
> > the CAL CUR setting, and the power will be reduced to control the current.
> > 
> > If the HI CUR message only shows up when driving the KPA100, then I 
> > would look for a problem in the input of the KPA100, or mis-calibration 
> > of the wattmeter in the KPA100.  If you bumped the setting for R26 while 
> > working on the KPA100, that in itself may be sufficient to explain the 
> > HI CUR indication.  Did you measure the actual power output with an 
> > external wattmeter or are you depending on the K2 display?  If the 
> > internal wattmeter is not properly calibrated, the actual power output 
> > can be much greater than indicated by the K2.
> > 
> > 73,
> > Don W3FPR
> > 
> > 
> > Andrew Lenton wrote:
> > > Hi Don,
> > >
> > > Thanks for that, Putting aside the K2's low power on 160, which no doubt has
> > > a component error value somewhere, the KPA 100 has been working at 111 Watts
> > > for two years until I disturbed the PA last week to make way for the DSP
> > > board. So something has happened to the KPA100. I only get a high current
> > > warning when the KPA100 is in use. 80 to 10 Metres is fine 11 watts no
> > > warnings! I think something has happened to the high power low pass filter,
> > > any thoughts?
> > >
> > > 73
> > >
> > > Andrew G8UUG
> > >   
> > >
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