[ARC5] Drift in BC-453 - more

Fri Dec 15 15:34:07 EST 2017

Hi
Some people spank (discipline) the computer and sound card timebases 
with atomic clocks or gps signals. However, I use WWV and reference to 
that. I'm an amateur and a Michigan hillbilly. I tune WWV's carrier from 
an AM radio on the spectral display and then line up a 10mc xtal 
oscillator superimposed on the 10mc WWV. It could be a 5mc xtal and wwv 
at 5mc. It's exactly the same only different. As your xtal oscillator 
pip on the spectral display moves onto the WWV pip you will see it climb 
up the side of the WWV pip. As it approaches zero the top of the pip 
will show some moire and when that is cleared up you are pretty darn 
close. Less than 1Hz. Maybe absolute zero. if you continue tweaking the 
xtal's pip will descend the other slope of the WWV pip. The soundcard 
and computer timebases are irrelevent (close stability). The VFO (HFO) 
in your receiver is irrelevant (close stability). Let them all drift and 
wander around. They will still show the relationship between your xtal 
and WWV. As long as computer oscillors don't jump around enough to make 
you go cross-eyed trying to look at it then it works perfectly. If your 
radio doesn't have AM mode you have to use more care in deciding which 
pip is the WWV carrier coming through your CW or SSB receiver. If it is 
FM just forget about it.

Connect you frequency counter to read the xtal frequency while the 
computer diplay shows it stable against WWV. If needed..tweak your 
counter so it shows 10.000000000000000000000000000000000mc. Wait a while 
to see if it drifts very much. It probably won't  Then measure whatever 
it is you wanted to measure with your frequency counter. Then check it 
against the xtal (still dead on WWV) and see if it changed. If it didn't 
then your counter is telling you what you wanted to know. If it did 
change you can mentally (use a calculator if you must) adjust the end 
reading by that amount.

This should work if you use something like CHU and an appropriate local 
xtal.

73,

Bill  KU8H

On 12/15/2017 02:14 PM, Bob via ARC5 wrote:
> Intersting comments on using the Computer to sort out drift parameters.
> I often wonder how the various clocks in the computer sound card and cpu
> clocks vote into the calculus?  Granted, some correction and validation
> of the computer's internal clock systems can be accomplished using
> external internet resources, but the question remains as to how accurate
> the computer sound card processes are.  Perhaps it's just that the
> calcuations in the computer's sound card DSP are done in the audio range
> that allows for sub  1 Hertz calculation?
>
> Cheers
> Bob, KE6F
>
>
> -----Original Message-----
> From: Bob kb8tq <kb8tq at n1k.org>
> To: Kenneth G. Gordon <kgordon2006 at frontier.com>
> Cc: Arc5 <Arc5 at mailman.qth.net>
> Sent: Tue, Dec 12, 2017 12:27 pm
> Subject: Re: [ARC5] Drift in BC-453 - more
>
> Hi If you are running a radio at 400 KHz, and a similar radio at 4,000
> KHz the drift of the second one (in Hz) probably will be 10X the drift
> of the first radio. The same applies if you go to 40 MHz (you now are at
> 100X vs 400 KHz). Yes, there are a bunch of assumptions there about
> radio construction, IF frequencies and various other things. To the
> extent this is “simple”, a 1 Hz drift on a BC-453 would be about the
> same as a 100 Hz drift on a similar radio on 10 meters or a 10 Hz drift
> on 80 meters. Simply put - if you *think* you could listen to SSB on 10M
> with a low IF / single conversion non-crystal based radio (ignoring
> anything but drift as a problem) … you should get about 1 Hz drift on
> the 453. You could compare to comfortably listening to SSB on 80 M as
> well. Of course, you immediately get into “drift over what period of
> time”. Any radio like this that I ever used for SSB stayed on pretty
> much all the time. Use it in the evening and leave it on all day while I
> was busy with other stuff. Starting from dead cold … yikes …. that’s a
> tough test for a tube based radio. If you *do* want to test for sub 1Hz
> sort of stability it’s likely easier to shove a stable signal into the
> radio and let a computer look at the audio coming out than to do a bunch
> of other crazy stuff. The advantage is that the result of the test is
> looking at the same thing the decoder software in the computer will be
> looking at. There are a lot reasonably stable oscillators on the auction
> sites to provide an adequate signal. The risk is more spending $20 and
> getting a dead one than anything else. Pretty much anything called an
> OCXO should do the trick. Lots of fun Bob > On Dec 12, 2017, at 2:57 PM,
> Kenneth G. Gordon <kgordon2006 at frontier.com
> <mailto:kgordon2006 at frontier.com>> wrote: > > On 12 Dec 2017 at 14:32,
> MICHAEL ST ANGELO wrote: > >> Bill, >> >> What is this millihertz spec
> for WSPR? I haven't tried it yet but I >> thought frequexcy stavility
> has to be a couple of hertz for the 2 >> minute cycle: >> >>
> <https://groups.google.com/forum/#!topic/2-meter-wspr/-hDK071K1iM> >> >>
> Mike N2MS > > Hi again, Mike. That spec is for 2 meters: it becomes far,
> far more critical at HF and MF. > Yes. Millhertz. > > Since, "Many
> WSJT-X capabilities depend on signal-detection bandwidths no more than a
>> few Hz. Frequency accuracy and stability are therefore unusually
> important." > > See this for details: > >
> http://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main-1.8.0.html#GENERAL
>> > In fact, someone on one of our lists mentioned something like <0.5
> Hz drift in 2 minutes or > less. I can't remember the details now, but
> his post included the link above. As I remember > it, he also told us
> that if the drift exceeded what I mentioned above, that would prevent >
> decoding of the input. > > I know that Bill Cromwell noted enough drift
> from the very slight drift in filament voltage by > line-voltage drift
> to cause very noticable drift. As he says, he decided to simply forego >
> attempts to use those modes. > > Although I am inclined to agree with
> him, I am very curious to learn if it IS possible to use a > BC-453 for
> these modes. I would guess not, but stranger things have happened. > >
> Ken W7EKB > > --- > This email has been checked for viruses by Avast
> antivirus software. > https://www.avast.com/antivirus > >
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