[Elecraft] K2 KPA100 Low Power Output Problem Mostly Solved

[Mike Walkington]

All,

After thinking the advice I got from several of you and trolling back
through the e-mail archives I found my problem.

A little embarrassing to tell you, but the cause of my low KPA100 output
power on all bands was due to a sagging power supply, but hopefully my
experience will help others :(  My paradigm (dastardly things that they are)
was thinking that the KPA100's current need was the total required. I forgot
to add in the basic K2's current needs!

At least my component identification, soldering technique etc was OK :)

Power output is now good on all bands except on 160 where I'm still
experiencing excessive current drain.

I still don't believe the results I got from scanning the LPFs with the
antenna analyser.  Specifically, what is the relationship between the SWR
results and the likely cut-off frequency?  What is the likely impact on
receiver performance?

Mike
VK1KCK
K2 #2599



-----Original Message-----
From: elecraft-bounces at mailman.qth.net
[mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Mike Walkington
Sent: Tuesday, July 05, 2005 6:00 AM
To: Elecraft-Reflector
Subject: [Elecraft] K2 - KPA100 Low Power LPF Performance

All,

I'm investigating low power output from my KPA100 and have scanned the LPFs
as suggested in the troubleshooting section.  My results were as follows:

Using an MFJ259 and having checked that MFJ output freq matches freq on K2
ie MFJ is aligned, I scanned low pass filters.  Here is the synopsis of the
SWR:

160m - Approx 1.0 from below 1.73MHz to 2.25MHz, climbs to 1.5 at 2.50MHz

80m - Approx 1.0 from 2.00MHz, starts climbing at 3.25MHz but approx 1.1 to
4.00MHz

40m/30m - Approx 1.0 from 5.00MHz, starts climbing at 9.25MHz (1.2),
10.00MHz (1.5), 10.8MHz (1.2), dips at 11.00MHz (1.0) and climbs again
11.26MHz (1.2) and 11.36MHz (1.5)

20m/17m - Approx 1.0 from 13.40MHz, starts climbing at 15.00MHz (1.05),
15.50MHz (1.18), 16.00MHz (1.2), 16.50MHz (1.35), past 17.00MHz over 1.5

15m/12m/10m - Approx 1.5 from 20.00MHz to 25MHz, dips 25.50MHz (1.2),
26.00MHz (1.15), 26.50MHz (1.0), stays down and rises at 28.00MHz (1.2),
28.50MHz (1.2), 29.00MHz (1.5)


Has anyone else scanned the filters in this fashion, especially for a KPA
delivering full output power/  If so, what were the results, ie I'm looking
to see what is considered normal. Did anyone else have LPF issues and what
were they?

Mike
VK1KCK
K2 #2599