Posted by
K5MMH on
Oct 04, 2019; 12:45am
URL: http://elecraft.85.s1.nabble.com/K2-Base-Low-Power-output-on-High-Bands-tp7655490.html
After a several month hiatus from radio, have discovered my K2/100 (S/N 3010)
has some issues with transmit power on some bands and a receive issue on 10m
and 12m. I am the builder of this K2.
In Feb. of this year, I wrote the reflector looking for help with “K2 base
low xmit power on all bands @ > 10 watts”. Don Wilhelm suggested “Since you
current draw at settings above 5 watts is excessive, I would first suspect
that T4 may have been wound for "better efficiency at 5 watts" - which
should not be used in a K2 that will be operated at greater than 5 watts
because it becomes more inefficient as the power is increased above 5 watts.
Check T4 to see how many white turns are on T4 - it should be 3 turns, but
if you find only 2 turns, rewind T4”. I checked the windings on T4 and Don
was spot on. The 3-4 winding (white wire) only had two passes thru the bino.
I removed it and re-wound both green and white wires. I went thru
transmitter adjustments again on pages 72 and 74. Now reading the output
power using my same setup gives the following results with power set to 10
watts, and read on the LP-100 watt meter:
10m = 7.70w @ 3.30A
12m = 7.10w @ 2.66A
15m = 9.70w @ 2.22A
17m = 10.10w @ 2.32A
20m = 10.50w @ 2.40A
30m = 10.00w @ 2.26A
40m = 10.70w @ 2.24A
80m = 11.20w @ 2.42A
160m = 10.80 @ 2.38A
I also replaced the PA transistors at that time, but did not replace Q11
and Q13
The above were the readings after rewinding T4 and replacing the PA
transistors in Feb. 2019.
Fast-forward to today. To perform the following tests, I have removed the
KPA100, removed the KSB2 (installed jumpers between pins 1-3 of J9 and J10,
C167 installed between pins 7-12 of J11), KNB2 removed (installed jumper
between pins 1-6 of J12), K160RX removed (installed jumper between pins 1-7
of J14). With power set to 10 watts, an Elecraft DL1 Dummy load connected to
load side of LP100 watt meter and the K2 BNC antenna port connected to LP100
watt meter, power supply connected to K2 DC barrel connector J3 (supplying
13.3 VDC), key-down using paddles connected to J1, reading current with K2
internal meter:
10m = 1.02 w @ 1.38 amps
12m = 1.81 w @ 1.46 amps
15m = 3.90 w @ 1.52 amps
17m = 3.70 w @ 1.52 amps
20m = 6.40 w @ 1.84 amps
30m = 8.30 w @ 2.26 amps
40m = 10.90 w @ 2.10 amps
80m = 7.10 w @ 2.42 amps
Then proceeded to Page 10 of K2 Appendix E and performed receiver signal
tracing in attempt to find receive issue on 10m and 12m. Here are the
readings using RF probe and external signal generator, comparing 30m and
12m:
PLL section Page 10, # 2 30m = .765 12m = .721
Page 10, # 3 30m = .310 12m = .341
Page 10, # 4 30m = .642 12m = .632
BFO section Page 11, # 1 30m = .448 12m = .445
Page 11, # 3 30m = .032 12m = .035
LPF section Page 11, # 9 30m = .132 12m = .054 >>>>>>> low
Page 11, # 10 30m = .126 12m = .036 >>>>>>> low
Page 11, # 11 30m = .042 12m = .021 >>>>>>> low
Page 11, # 12 30m = .039 12m = .020 >>>>>>> low
So, I am seeking assistance on correcting the low power output on the high
bands and the receive issue on 10m and 12m.
Thanks for your assistance
Mike Harang
K5MMH
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