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
--
|