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Re: Low Power ?

Posted by Don Wilhelm-3 on Sep 19, 2004; 2:26pm
URL: http://elecraft.85.s1.nabble.com/Low-Power-tp370386p370395.html

Larry,

The K2 is speced for 10 watts out on all bands with a 13.8 volt power
supply, and most are capable of about 12 watts on the higher bands (10/12
meters) and 15 watts on 17 meters and below.  Recall that there is a menu
entry (secondary menu) that sets the power limit on 10 meters - it defaults
to 10 watts.  If you are checking for maximum power on that band, you may
want to temporarily set that value to 15 watts.

You could first try repeaking the bandpass filters - the K2 typically has
more gain on 40 and 30 meters, so your low 40 meter output gives me
suspicion.

The most common reason for low power output is T2.  T2 should be wound so
that the secondary (green wire) is spread over most of the primary turns,
and it should be mounted above the board by about 1/16 inch (2mm).  You may
want to download the latest manual and look at the illustration for T2.

Also check T4 - make certain it has the proper number of turns and that it
was not wound for maximum efficiency at 5 watts.

Last but not least, be certain your wattmeter is correct - many are not, and
be certain your dummy load is actually 50 ohms resistive on the band you are
investigating.  If you have a calibrated 'scope with a frequency limit of 50
MHz or more, you can check the wattmeter by observing the RF voltage across
the dummy load.  Power can be calculated as the square of the Peak to Peak
Voltage divided by 400 for a 50 ohm load (yes, you can do all the peak to
RMS conversions and arrive at the same thing - I will leave the proof to the
'student').  An RF probe can also be used to measure the RF voltage, and in
that case the probe shows RMS voltage and the power is calculated as V**2/R.

73,
Don W3FPR

----- Original Message -----

I wonder if my K2 (Serial # 2424 with latest mods and software) is set up
correctly and would appreciate comments.  Output power with CAL CURR set at
3.0 amps is as below.  Increasing CAL CURR to 5 amps makes little
difference.  I know that the K2 is basically a 10 watt rig and I get more on
some bands, but the upper bands do not achieve this.  When using the K2 with
my KW1000 Linear Amplifier a watt or two makes a difference.
80 Meters = 13.0 watts out
40 Meters = 10.0 watts out
30 Meters = 12.0 watts out
20 Meters = 11.0 watts out
15 Meters =  8.0 watts out
12 Meters =  9.5 watts out
10 Meters =    7.0 watts out



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