Re: LF: Softrock RX divider IC problem, unexpected frequency out

[M0FMT <peteg8fmt@gmail.com>]

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

On Fri, Jan 26, 2018 at 10:16 PM, Chris Wilson <dead.fets@gmail.com> wrote:

Hello Tobias and everyone else.


Thanks for the detailed info, much appreciated.

I  managed  to change the divider again, but this is probably the last
time  as  a pad is lifting. I also put back a 22k resistor for the 10K
R16.  The  new  divider  one  didn't  have any output at all, save the
tiniest  bit  of  ripple:(     So  I  put  back the 10K and output was
intermittent  and  much  like  before.  But I noticed if i touched the
divider  on its plastic shell the the thing gave a much better output,
good  square waves, but they would either stop themselves, or if power
to  the board was removed then re-applied, it wouldn't start. The input
was   on  frequency  and  strong. But now I could sometimes just hover
a  finger  right  above  the divider chip and it appeared a capacitive
effect would start it.

When it did output clean square waves they too were on frequency.
There was a proper 90 degree phase shift. I then put in a 6.8k for R16
and it's better still. Dare I go lower, or is this telling me
something I am not hearing?I haven't changed the crystal yet. I don't
think the issue is now the oscillator itself, but driving the divider.
I am sure Andy is right that a Schmitt trigger buffer would be best,
but I didn't really want to start redesigning something I know others
have had running 24 hours a day with superb results.

I'll  upload the oscillator wave form at pin 3 of the divider as it is
now.

http://www.gatesgarth.com/newR17-to--pin3.jpg


Friday, January 26, 2018, 9:33:04 PM, you wrote:

> Hi Chris !

> The first screenshot shows an un-symmetrical square-wave that will
> generate two frequencies to the 1:4 divider and Tayloe-mixer. An FFT of
> this signal (R17-to-pin3) should show two peaks and not only one as
> expected. A standard frequency counter will show only the arithmetic
> mean value of both frequencies, as it is just adding zero-crossings
> during gate-time.

> The Softrock series 6.x had a different type of I/Q divider that used
> three flips-flops. They did not have a problem with such an
> un-symmetrical square-wave, as there was an inherent divider by two,
> which forced the oscillator signal to be symmetrical to the mixer.

> You could try to move the bias-level of Q2 transistor to a voltage where
> the output (square-wave) signal of Q2 will be almost symmetrical.
> If the oscillator at Q1 is not running smoothly, this is where to look
> for variations of C's or R's to make it run stable.

> 73 de dg3lv Tobias

--
Best regards,
 Chris                            mailto:dead.fets@gmail.com