[Elecraft] KPA 100 Low power on 160M

Mon Oct 27 05:37:47 EST 2008

Hi Don,

I am sorry I should have said:

The K2 with the  KPA100 removed behaves normally, current
does not exceed 2.5A on any band at full power (between
10-17 Watts depending on band 40M I get the most power)

I have retuned 80 and 160M and I have checked all the
components for correct value C11,12,13,14,15 + 16, L34 +5,
160M board checked C1,2 and 3 and L1 and L2 for 21 turns.

Now UK band is 3.5 to 3.8Mhz 300 KHZ wide 80 Metre gives
full power where ever I centre tune 3.6, 3.65, 3.7 or 3.75
MHz, now top band I get 15 Watts if I tune at 1.9 MHz drops
off a bit at 1970 upwards, and also 1840 downwards, however,
in dB terms lest than 1.5dB across the band, looks worse in
watts when you see 15 drop to 10! I have compromised top
band to give the max output between 1900 and 2000. It is
better than it was.

With your help, I am beginning to think that the input match
to the KPA 100 is not 50 OHMS on top band, hence the high
current warning( High return loss). I will replace the
co-ax, as a start, and measure S11 and S12 form my network
analyser, and check the match into the KPA100 and report
back, it is odd the other bands seem happy with the match. I
must of damaged something somewhere removing the KPA100.

73's

Andrew

> Andrew,
> 
> FB on all of that.
> Before doing anything else, remove the KPA100 and run the
> base K2 into a  dummy load.  With the power at maximum,
> note the current draw during a  TUNE (press DISPLAY to see
> the voltage and  current).  Do that on 160 as  well as on
> 80 and 40 (to compare the current per band).  If you
> receive  a HI CUR message, increase the CAL CUR setting
> (up to 4 amps) to see if  it goes away.
> 
> If the 160 meter power output and current draw is similar
> to the other  bands, then you can say the base K2 is OK
> and look for a problem in the  KPA100. (the current draw
> at max power will normally be lower on 40  meters). The
> problem can actually be in the base K2 160 meter LPF - the
> above test will reveal it if present.
> 
> 73,
> Don W3FPR.
> 
> 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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