[Elecraft] KPA 100 Low power on 160M
a at lenton.org
a at lenton.org
Tue Oct 28 05:07:08 EST 2008
Hi Don,
Set up: KPA100 powered up connected to K2 only the Aux RF
plug disconnected. 50 ohm load connected to RF O/P
Ok I measured the return loss into the KPA100, the loss is
6-7dB on 1.9 MHz, so an SWR of 2.5 to 1! on 3.5 to 24 MHz
less then 1.3 to 1 and rises a bit towards 29MHz. I did not
have a lot of time last night as it was a club meeting, so
will make some more measurements tonight and get back.
73
Andrew
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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------------------------------
Message: 3
Date: Mon, 27 Oct 2008 08:25:10 -0400
From: Don Wilhelm <w3fpr at embarqmail.com>
Subject: Re: [Elecraft] KPA 100 Low power on 160M
To: a at lenton.org
Cc: elecraft at mailman.qth.net, don at w3fpr.com
Message-ID: <4905B326.6010601 at embarqmail.com>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Andrew,
OK, sorry for the 'dumb' response, but I had to check it out
so there
would be no 'tail chasing' in a non-problem area.
Yes, it would seem that the input to the KPA100 is nowhere
near 50 ohms
on 160m.
I don't know the vintage of your KPA100, but if it does not
have blue
toroids at RFC1 and L16, now would be a good time to install
KPA100UPKT. That change was mostly to the T/R switch area,
but still
can impact the input circuit response.
You can check out the KPA100 LPF easily with an antenna
analyzer - put
the base K2 into CW TEST just to be safe, and set the power
less than 11
watts. Pull the input coax from the RF Board and insert a
51 ohm
resistor. Switch to 160 meters and connect the analyzer to
the SO-239
connector. The K2 and KPA100 must be powered (and the
ribbon cable
connected) because the KPA100 relays are not latching types.
The SWR
should be less than 1.5 over the entire 160 meter band.
You could try running the antenna analyzer into the KPA100
input
(connect the output to a dummy load since some power may be
developed at
the KPA100 output). If you set the K2 power to less than 11
watts, you
will be reading only the KPA100 LPF, but when the power is
set at
greater than 11 watts, you should read the input impedance
of the
KPA100. I have never actually done this measurement, so I
don't know
what is normal, but you could compare with the results on 80
and 40
meters as a sanity check.
73,
Don W3FPR
a at lenton.org wrote:
> 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
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