[time-nuts] EFC tracking

WB6BNQ wb6bnq at cox.net
Sat Jun 26 20:02:16 EDT 2010


Hi Steve,

Let me build on the VFC idea for a minute.  If I am understanding your interest
properly, you are wanting to monitor and track the EFC changes then process that
information as a form of studying the stability to some degree.  Is that correct ?

Well, it occurred to me, admittedly after the fact, that there are several programs
written for Amateur radio use to receive and observe very slow CW on the really long
wave radio frequencies, like 160 to 190 KHz.  These programs provide the waterfall
type displays among other types and, I think, they store the sessions as a file for
later review.  As I am only familiar with the fact they exist, I have never used them,
you would have to peruse their abilities to see if there is a fit.

The primary point is they use a computer sound card to look at the audio out of a
receiver.  That audio is somewhere around 1KHz.  I am not sure what kind of
sensitivity the software has as to resolution, but I believe a number of Amateurs,
including some on the list, have used such for the "FMT's" (frequency monitoring
contests) with fair, if not better then fair, results.

The software may do all you want or at least a major portion that being the file
creation and storage, hopefully in a raw PCM format (i.e., no compression.  I am not
sure what is required for the circuit of the VFC these days but it shouldn't be
anymore complex then that of building up a CPU and so forth.

Good luck with the project,

73....Bill....WB6BNQ

Steve Rooke wrote:

> Bill,
>
> On 27 June 2010 01:21, WB6BNQ <wb6bnq at cox.net> wrote:
> > Steve,
> >
> > I think using a voltage-to-frequency converter would solve that problem.  They
> > are not too expensive and there are several flavors from Amalog devices and some
> > others.
>
> I just had one of those duh! moments :) It does make the sampling a
> little more complicated as I'd have to take a number of samples and do
> something like a FFT to get the frequency, I think. My idea seemed
> just a simple way to just make a single, or limited number, of
> sample(s) and I have the data. Still, this is a good idea and I'll
> have a good thunk about it.
>
> > Just set it for a 1KHz start point or maybe 10KHz.
>
> Thanks for your advice,
> Steve
>
> > Bill....WB6BNQ
> >
> >
> > Steve Rooke wrote:
> >
> >> I would like to track the EFC voltage in hardware using something
> >> cheap and ready to hand. I was thinking of using a sound card as it
> >> has good resolution but it's obviously only AC coupled so it would not
> >> measure the DC of the EFC. I thought about modifying a sound card to
> >> make it DC coupled but most of them seem to reference the 0V point to
> >> some internal reference voltage hence there is a DC shift there. I
> >> next thought about turning the DC into AC by chopping it, IE.
> >> inverting 50% of the voltage via an oscillator. This way I could pass
> >> the square wave directly into an unmodified sound card, take
> >> measurements and then do an RMS calculation on them (really just need
> >> to flip the sign on, say, the negative readings).
> >>
> >> I wonder if anyone has done something like this before and could share
> >> their experiences. I've attached a diagram image (hope it is accepted
> >> by the list) which is my first go with Eagle so I'm not exactly very
> >> familiar with it, sorry. The R's and C's in the astable would be set
> >> to a clock frequency that enables this to work without bias given the
> >> sampling frequency. I'm not sure if this clock should be slower than
> >> the sampling frequency or higher, just haven't got my head around that
> >> yet. The R's around the op-amp would need to be set in a ratio that
> >> transforms the EFC voltage into the range that the sound card can
> >> handle (that is yet to be calculated by measuring the limits). If you
> >> have any suggestions or ways of doing this in a better way, I'd be
> >> very grateful for the advice.
> >>
> >> Thanks,
> >> Steve
> >> --
> >> Steve Rooke - ZL3TUV ? G8KVD
> >> The only reason for time is so that everything doesn't happen at once.
> >> - Einstein
> >>
> >>   ------------------------------------------------------------------------
> >>                  Name: DCchop.png
> >>    DCchop.png    Type: PNG image (image/png)
> >>              Encoding: base64
> >>
> >>   ------------------------------------------------------------------------
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> >
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>
> --
> Steve Rooke - ZL3TUV & G8KVD
> The only reason for time is so that everything doesn't happen at once.
> - Einstein
>
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