[Elecraft] K1 signal traced

[Don Wilhelm]

David,

Note that all the RF voltage values at the buffer output and after are 
much lower on 20 meters than on 40 meters.  That points the finger at 
the Buffer stage.

Even though the MIX output is lower than expected, for right now, I 
would suggest you concentrate on the major difference in the BUF output 
between the 2 bands.  The buffer is frequency sensitive - note that 
capacitor C16 in series with R11 makes the gain change with frequency.  
The gain should be higher on higher frequencies, and in your case it is 
not.  So check the component values at C16, R11, and R12 as well as the 
soldering for those components (they determine the gain of U9).
In addition, do DC voltage measurements at U9 pin 2 during both transmit 
and receive.  If Q14 is doing its job, you should see a low voltage at 
pin 2 during receive and about 6 volts during transmit.

Yes, those values indicate that the PreMixer crystal for 20 meters is 
probably OK (reserve judgement on that for later).

73,
Don WFPR

On 3/19/2013 7:46 PM, David L DuPuy wrote:
> Don,  here are the values for the Transmitter Signal Tracing.  Results are
> shown for 40m (all okay except maybe MIX), and on the right are results for
> 20m, as measured on a 60 Mhz Tek oscilloscope.  The problem seems to start
> between OSC and MIX, i.e., at U8 Transmit Mixer/Osc.
>
> signal tracing
>
>               40m 20m
> shunt DRV to gnd
> PRE      0.09 0.06
> ATTN    0.05 0.05
> OSC      0.06 0.07
> MIX      0.05 0.05  LOW
> BUF      4.3 0.9    LOW
> TR1      2.3 0.5
> BPF      0.4 0.2    LOW
> TR2      0.4 0.2    LOW
> TR3     0.01 0.04  HI
> remove DRV shunt
> DRV     1.3 1.1
> PA     40 5.4    LOW
> ANT     40 5.0    LOW
> RFD     2.1 0.59  LOW
>
> I'm having trouble understanding how the waveform at PRE and ATTN is the
> same amplitude on 40 and 20, but very different past U8.  The signal at PRE
> and BF is not a clean sine wave, but shows a modulation... true for both 40
> and 20.  Is that normal?  The PRE and BUF 20m signal appears to be double
> the 40m frequency.  I presume that means both X1 and X2 filter board
> crystals are operating??  I really appreciate your continued help!!  (you
> are very patient!)  David  AC4BN
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>