Not only can our ears not detect much below 30 Hz, our radios don't do too
well with that frequency and below, either. Most cut off 'around' 100 Hz.
For those who must split hairs on frequency accuracy, WWV suffers
variations depending on propagation and short-term variations (Doppler) due
to an unstable ionosphere, even in these days of minimal solar activity.
I'm fortunate in that I receive WWV at 2.5, 5.0, 10.0, 15.0, 20.0 and 25.0
MHz 'mostly' via groundwave (near Berthoud, Colorado). WWVB is on 60 kHz
and on long paths (like the east and west coasts), does not suffer the
Doppler variability that the HF signals do.
If you want the ultimate without ionospheric modulation, procure a GPSDO
and use that as your frequency standard. Mine typically runs in the couple
of parts in 10 E 11 on the 10 MHz output. Occasionally, the display
indicates a bit better (and worse), but is far better than ionospherically
propagated HF WWV. I believe AirSpy is now selling the Bondar GPSDO (no
connection).
Another excellent application for this purpose is Spectrum Lab, <
>, as opposed to FIDIGI. Softpedia
also offers it. It's freeware and has become pretty much the standard for
the VLF and ELF'ers. I use it extensively for meteor scatter from distant
DTV signals.
Dave - W?LEV
On Sun, Jan 12, 2020 at 7:15 PM Lawrence Macionski via Groups.Io
<am_fm_radio@...> wrote:
David GM8ARV-
Yes, the ADAFRUIT white page on their SI5351 board I linked to does elude
to setting the frequency to 1ppm. I have found and knew it for years, "ZERO
BEATING" to WWV doesn't work, because humans can't hear lower than 20-30
cycles depending on age and history with cannon fire.
For those who are not hams FLDIGI is a program for decoding various ham
radio digital modes. It uses a computer sound card to display frequency
versus time versus intensity (amplitude) in a waterfall display. It has
audio frequency readout. Now before someone pipes up - "Well how do you
know that's accurate?" We don't .. but what we do know is that WWV and
it's carrier is accurate, by superimposing our NanoVNA CW mode signal at
10.0000 or injecting it into the same receiver using nearby antennas.. we
can see the WWV carrier and the NanoVNA carrier and see the frequency
difference on the waterfall display. In my case it's 110 cycles. WWV is
also at 5.0000, 15.0000, 20,0000 and there is also CHU Canada available.
So, these days we don't need a capacitor to change, or slug tuning.. Even
the SI5351 data sheet specified a crystal in the 25-29 mhz region.. That's
because somewhere we deposit a number in a register that aligns the
accuracy of the output of the SI5351.. granted to enviromental tolerances,
but for a $50 "gizmo" that is in use world wide, that's fantastic.. I
started with a US Army Signal Corps BC-221-AF frequency meter, which was
the "best you could get" when I got my 1st class Commercial Radio Telephone
license in 1971.. Cause a Service Monitor was $1000's. Now go read how to
use a BC-221 and we could meet and do better than commercial standards.
Back then we'd use a heathkit oscilloscope and display the oscillator
"standard" versus the unknown oscillator and produce a Lissajous pattern
and using a twiddle stick, get the pattern to look like an "O" and try to
stop it from rotating. In the Detroit area we were homebrewing 100.0 cycle
PL''s and used a 5:3 Lissajous pattern against 60 cycles. Detroit Edison AC
was our frequency standard..
Larry W8LM
--
*Dave - W?LEV*
*Just Let Darwin Work*
*Just Think*
