In article , Robert Casey
writes:

Creative PLL and DDS subsystems of today, designed by others,
make it possible for anyone to select 10 Hz increments on any
HF band (30,000 frequencies within 300 KHz) with crystal-
controlled accuracy.

Analog VFOs are continuously variable. Making it possible for anyone
to select an *infinite* number of "increments" within a 300Hz
bandwidth much less your coarse 300 Khz wide example.

Sure, but those old VFOs tended to change the frequency a little
over time. AKA "drift". Me thinks one desires to select a frequency
and then have the rig stay put on it. Modern rigs can do that
to the accuracy and drift of a good crystal oscillator to some
set resolution. But for our uses, 10Hz resolution is more than
sufficient.

That's a good summation, Robert, thank you.

10 Hz increments has been regarded as sufficient for quite a number
of years.

It all depends on the internal reference oscillator being trimmed to
the frequency it is supposed to be working at. A careful check
against WWV (for those receivers that can tune to 5, 10, or 15 MHz)
will prove that out. Since the same reference oscillator is used for
generating the transmit carrier, it will be as accurate as the receiver
once calibrated.

In the case of the mixing-by-crystal-banks plus VFO (or "PTO" for
most Collins radios), there was a dependency on the quartz
crystals being correct. Those were typically in the 30 to 50 PPM
(plus-minus) accuracy by themselves. That was GOOD accuracy
for the 50s to 60s time frame...but one band might be off on the
low side while another band might be off on the high side.

With TCXOs or VTCXOs (Temperature Compensated Crystal
Oscillators, fixed or Voltage-controlled), the drift on modern
"all band" (HF that is) transceivers can be within 1 PPM after
calibration. The old Collins "PTO" (Permeability Tuned
Oscillator) achieved stability of 50 to 100 PPM over a full
military temperature environment (-55 C to +85 C) but they
were not inexpensive. Collins amateur equipment was often
at the top of the money line when they were marketing for
the hams.


Early 2 meter synthesized rigs had some trouble with this (the
phase noise would "add" to the FM modulation and produce extra
noise. Phase modulation and frequency modulation are closely
related, one is the integral (as in calculus) of the other.

PM and FM aren't related "integrally" other than their modulation
product series expansions are extremely close, different primarily
on the signs of the series terms...thus requiring different
equalization of analog modulating signal frequencies. "Carson's
Rule" applies equally to both to estimate bandwidth versus index
of modulation.

Besides, "real hams" don't use any FM on HF...they hardly
ever go above 30 MHz. :-)

As for HF CW, some poorly designed novice xtal oscillator
circuits probably had it worse than a modern synthesized rig.
And then there's chirp...

That's a fault of design, not the basic frequency control system.

If your "chirp" refers to on-off keying CW modulation, that's a
result of inattention to the rise and fall times of the keying plus
the stability of the power supply. Quite a different matter.

The subject has gotten out of hand in here with all the PCTA
extras eager to beat on any NCTA by taking a phrase out of
logical context. :-) Those all have expensive ready-builts in
their "shack" and - naturally - those rigs are the closest thing
to perfection as anything. They don't seem to know squat
about the inner technology involved in frequency synthesizers
so they want to "get even" with anyone who does. Sigh.