[Elecraft] K2 Base Low Power output on High Bands

[Don Wilhelm]

Mike,

The current draw now looks to be in line with the power output, but your 
output drops off with increasing frequency.

First measure the voltage at the base of Q7 and Q8 during transmit.  If 
it is not in the range of 0.60 to 0.64 volts, replace Q11 and Q13.

Since you are measuring the receive signal path, and have verified that 
the internal K2 signals are OK, you apparently have a problem in the T/R 
switch or the Low Pass Filter.  I suspect the T/R switch first.

Make certain all the RFCs in the T/R switch are not open - including the 
RFC3 toroid, and check the orientation of diodes D1 through D5.
In receive, do you have 8 volts at the anode of D4?  The cathodes of D3 
and D4 should be at least 0.4 volts (preferably 0.6 volts lower than the 
anodes.
Is RFC3 wound on a gray ferrite core?  If wound on a black core, that is 
your problem.

Once you do those checks, skip to the Transmit Mixer, Buffer, Bandpass 
Filter, T/R Switch tests during transmit (or TUNE) on page 14 of the 
manual Appendix E.  At which point in the sequence does the RF voltage 
drop significantly lower than the Expected value - ignore any RF 
voltages which are higher than the Expected value (except for the T-R 
Switch #1 which should be lower than Expected).

73,
Don W3FPR


On 10/3/2019 8:45 PM, K5MMH wrote:
> 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.

> 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.
>