Hello all.
Today when powered up there was rarely any output from the divider at
all, so I started again.
I decided to try two things, build a little test rig with a spare xtal
of the same 461.5kHz as the one in the RX with the same C10 at 3900pF
and C11 at 2700pF on a bit of pcb and excite it at 1v P to P sine wave
from my sig gen around the xtal frequency and look at the output on
the scope. That failed abysmally, no change in display, thinking about
it maybe it's due to the big capacitances involved?
Anyway, back to the RX. C12 at 680pF, C10 at 3900pF and C11 at 2700pF.
Waveforms taken with scope at DC coupling, but V scaling changes. I
believe (dangerous with my lack of knowledge..) that C10 to base of Q1
is good. Base of Q2 looks ok. But with R16 at the recommended 10K I
see half a sine wave at the emitter of Q2. With the original 20k (I
don't have the oddball 20.1k around) the waveform is still part
complete and of a much lower amplitude.
Is this a bias issue with Q2 or something else please?
I hope the file names are self explanatory! Note that V axis scaling
changes in some shots!!
Thank you for all your help!
The schematic for the modded Softrock Lite II in question:
http://www.gatesgarth.com/schematic2.jpg
Scope screen captures:
http://www.gatesgarth.com/lf-base-q1.jpg
http://www.gatesgarth.com/lf-emitter-q1.jpg
http://www.gatesgarth.com/lf-base-q2.jpg
http://www.gatesgarth.com/lf-emitter-q2-r16-at-10k.jpg
http://www.gatesgarth.com/lf-emitter-q2-r16-at-22k.jpg
Friday, January 26, 2018, 11:52:20 PM, you wrote:
> Hi again
> Well all seems well if you are getting a good wave at the flip flop
> output. Just a comment about your input wave forms yes the MF does
> show a second harmonic petty low and as you have said the MF version
> works OK. Please remember a square wave is in fact and infinite
> number of harmonic frequencies so this is not an issue the dominant
> wave is overwhelmingly the fundamental so that will be processed
> into a square wave by the Flip Flop. If the drive to the
> multiplexer is good as you say (I can not open the JPG but it
> doesn't matter) it sounds like the local oscillator divider chain is
> correct. I can only conclude the instability reported is at the
> oscillator suggest you concentrate on that as a source of your
> problem. ..... I have run out of ideas.
> Anyway good luck and please report the solution there are a lot of
> people very interested. 73 petefmt
--
Best regards,
Chris mailto:[email protected]
|
