One listens not to the two tones, in an effort to discriminate them, but
rather to the slow "thrummmm thrummmmm...." that repeats at very low speeds
when you get the tones close. That is, the amplitude of the thrummmm builds
and fades at the beat frequency.
You can hear this when you tune a piano, and the beating goes away when the
two strings are matched. Some of us like to tune our pianos for a little
"roll" to add a certain sound, and so you then tune the strings so the
thrummming is slightly there.
One used to hear this occasionally on older airplanes also, where two piston
engines would be slightly apart in speed. You could hear a very slow
build-up and drop off of the amplitude of the sound, until the pilot matched
speeds. Of course you don't hear that any more with modern equipment.
Has not a thing to do with your ability to hear, say, a 30 Hz tone. The
thrummm that you hear, while I never measured it, is at a much higher
frequency than that....perhaps a couple hundred Hz or so. But it Varies
very slowly in amplitude over time - that is, at the beat frequency.
73 de Gary, AA2IZ
----- Original Message -----
From: <CATFISHTWO@aol.com>
To: <tentec@contesting.com>
Sent: Monday, January 09, 2006 9:37 PM
Subject: Re: [TenTec] [Orion] O2 versus Orion
>
> I enjoy this on the orion, but you will never ever keep up with my swan 3
> drifty, now that's accurate freq's
>
> In a message dated 1/9/2006 9:42:00 A.M. Pacific Standard Time,
> RMcGraw@Blomand.Net writes:
>
> My experience tells me that there is a concernable difference in ones
> ability to audibility and accurately "zero beat" a given signal. Unless
one
>
> can observe the difference in beat of the two signals via the S-Meter
> fluctuations as the frequency gets very close, it is thus below the audio
> passband of the and certainly below the low frequency hearing of most
folks.
> Less than 30 to 50 Hz for example. Therefore the 1 Hz resolution or
ones
> desire to achieve such is of rapidly questionable accuracy.
>
> To this end, I prefer to actually measure the transmitter output or
actual
> oscillator frequency with a suitable counter capable of measuring to 0.01
Hz
> at the desired frequency or better. Truthfully, not many hams have
access
> to such high accuracy items as their cost is several times that of an
Orion
> II. Thus we do more "referencing" than actually measuring of frequency
> values. In each case, the reference add a percentage of error +/- to the
> resolution method.
>
> I took some time to "practice" various zero beat methods this morning and
> then looked at the actual transmitter frequency. In most cases I was
able
> to get within 30 to 50 Hz of the desired frequency but certainly in fact
no
> closer, as the audio passband fell apart below 30 Hz and there was simply
> "nothing to hear" coming out of the receiver. Once I got closer in
> frequency then I was able to detect the swing of the S-Meter and bring
> things in a good bit closer. Still, accuracy of 1 Hz was questionable.
>
> We must remember that these radios are not designed to be frequency
meters
> or frequency counters and thus the stability and repeatability is very
> questionable when one gets into the single digit Hz region. Then why do
> they put 1 Hz resolution on radios? To be better than the next fellow
and
> to sell radios with features.
>
> 73
> Bob, K4TAX
>
>
> ----- Original Message -----
> From: "Martin AA6E" <martin.ewing@gmail.com>
> To: "Bill Tippett" <btippett@alum.mit.edu> > standard for WWV
comparison.
> >
> > Now that I look at the schematics, I see that the CODEC has a separate
> > "14.360 MHz" clock crystal. Maybe that's the problem. It should be
> > generated from the TCXO. Is that the birdie I hear at 14,351.770?
> > (.05% low) This would introduce a minor offset, which is cancelled
> > out if you calibrate against WWV. Or is there more to it?
> >
> > Orion's accuracy and stability are good, but none too high, IMO. This
> > shows up in netting accuracy at the higher freqs. Of course, 95% of
> > rigs out there are worse. The new IC-7000 has a much better spec:
> > +/- 0.5 ppm vs Orion's +/- 3 ppm. Probably cost them a couple of
> > bucks more. The IC-7800 claims +/-.05 ppm 0-50C "after warmup", for a
> > price.
> >
> > It would be nice if the master oscillator was at least upgradeable or
> > syncable to an external reference, for the few folks who are looking
> > for very high precision.
> >
> > 73 Martin AA6E
>
>
>
>
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>
>
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