[ARC5] Drift in BC-453 - more

Fri Dec 15 16:44:13 EST 2017

Hi

We’ve gone around a bit on accuracy vs stability vs wander vs temperature drift. That makes things a bit 
confusing. They very much are not the same thing. In some cases they overlap, but not always the way
you might expect.  

Your typical sound card has a single crystal running it’s timebase. The stability of the tone in generates 
will be roughly what the stability of that crystal is in the computer’s thermal environment. If the temperature
is fairly constant, it will hold a ppm or three. If the temperature ramps up and down by 10’s of degrees as
you play your video game ….. it may move around a bit. 

One ppm is one Hz at a MHz. At any of the frequencies involved with a BC-453, a ppm is a fraction of a Hz. 
Expecting the sound card to hold less than a hertz over a few minutes to a few hours is not unreasonable 
in the BC-453 case. That assumes the computer isn’t doing crazy stuff and your sound card doesn’t have
some really odd parts in it. 

Lots of fun ….

Bob

> On Dec 15, 2017, at 2:14 PM, millerke6f at aol.com 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 <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 <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 <https://www.avast.com/antivirus> > > ______________________________________________________________ > ARC5 mailing list > Home: http://mailman.qth.net/mailman/listinfo/arc5 <http://mailman.qth.net/mailman/listinfo/arc5> > Help: http://mailman.qth.net/mmfaq.htm <http://mailman.qth.net/mmfaq.htm> > Post: mailto:ARC5 at mailman.qth.net <mailto:ARC5 at mailman.qth.net?> > > This list hosted by: http://www.qsl.net <http://www.qsl.net/> > Please help support this email list: http://www.qsl.net/donate.html <http://www.qsl.net/donate.html> ______________________________________________________________ ARC5 mailing list Home: http://mailman.qth.net/mailman/listinfo/arc5 <http://mailman.qth.net/mailman/listinfo/arc5> Help: http://mailman.qth.net/mmfaq.htm <http://mailman.qth.net/mmfaq.htm> Post: mailto:ARC5 at mailman.qth.net <mailto:ARC5 at mailman.qth.net?> This list hosted by: http://www.qsl.net <http://www.qsl.net/> Please help support this email list: http://www.qsl.net/donate.html <http://www.qsl.net/donate.html>
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