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Before you pass this by, thinking an idiot out in ham land can't calibrate a NanoVNA OPEN,SHORT,LOAD, THRU..... I'm not speaking of that calibration, which i found excellent in a paper "“Factory” Calibration Considerations and Procedures for the NanoVNA" That document is an expansion of Message# 233 from this groups.io website. Mostly the work of Alan Victor, W4AMV and his colleague Gary O’Neil, N3GO. That re-write and the additional material is the work of Larry Goga, AE5CZ. Kudo's

Instead - What I'm talking about is above my paygrade as I know the calibration I want is not covered. Playing with my NanoVNA; I set up a CW signal (from the touch pad) of 10.000Mhz and compared it against WWV on my ICOM 756proII using FLdigi waterfall to measure my NanoVNA frequency. My NanoVNA 110 cycles high at 10.000.00 against WWV. At least on my frequency counter I have a trimmer to zerobeat WWV.

I did a search of SI5351 and tried to figure there must be some sort of "master adjust" register as I'm thinking any ham could and should be able to bring the master frequency to within a few cycles. Especially when working with harmonics. It is described here:



I have done the "warble" in the discription where you can count 4 cycles per second adjusting my freq. counter... The paper was written by Jim N?TKN.

It's above my paygrade to develop this calibration into the NanoVNA. Any thrill seekers want to step up to the plate? Perhaps some sort of Stand alone "SI5351 master flash".program that tweaks the SI5351 and writes it through the USB cable..apparently the SI5351 can save the tweak value.

Advise.

Larry W8LM

Is there a crystal somewhere? What are its tuning capacitors? And what is its load capacitance? Any room for a trimmer?

My answer above means, as you probably know, that you can fine tune the frequency of a crystal by changing capacitors around it.

The nano's have a TCXO module which is not adjustable. The schematic shows a DAC freq trim control line from the uP but I believe all the nano's, beyond perhaps the first ones made, have a TCXO that is not adjustable and their Vcontrol line on the TCXO does not exist. The pad on the TCXO for VC position is just grounded through a zero ohm resistor. You can replace the TCXO with one that does have a Vcontrol but I would not recommend it. The TCXO temp tracking is 0.5 ppm over temp. The initial build tolerance is 1.0 ppm.

The Si5351 has the ability to warp a crystal resonator but since the nano's feeds a clock from the TCXO the warping function will not work.

If you are in fact getting 110 Hz off freq at 10 MHz freq setting you are 11 ppm off freq. This would only be possible if you had a TCXO that did have Vcontrol and it is grounded. You can remove the zero ohm chip resistor to ground on the TCXO Vcontrol pin and put a 0.6v to 3.3vdc variable supply on the pin and see if the freq moves indicating you do have a TCXO with Vcontrol.

The Si5351 has a lot of spurious frequencies and you might be zero beating one of them by mistake.

The nano's should be less then 1 ppm for frequency tolerance.

It is possible to tweak the synthesizer frequency setting to account for any TCXO tolerance. I don't think this function is written into the firmware and if it is not it might be something that could be put in future firmware. There would be a calibration register in Flash memory for freq offset and the firmware would calculate the required synthesizer setting offset to the desired freq.

PS. also not sure how accurate you can be with zero beating. There may be a demodulator low freq rolloff issue..

From: roncraig1@...
[]
It is possible to tweak the synthesizer frequency setting to account for any TCXO tolerance. I don't think this function is written into the firmware and if it is not it might be something that could be put in future firmware. There would be a calibration register in Flash memory for freq offset and the firmware would calculate the required synthesizer setting offset to the desired freq.
===========================================

Whilst the NanoVNA series are not designed as high stability frequency standards, I do agree that having the ability to set a "ppm" value for the master oscillator would be a very useful enhancement.

Copied the suggestion to the NanoVNA-F group.

David GM8ARV
--
SatSignal Software - Quality software for you
Web:
Email: david-taylor@...
Twitter: @gm8arv

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

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*

You can get much better than 20Hz by watching S meter, when you are very close it will swing due to constructive and destructive action on the signal. Get the S meter to nearly stop swinging and you will be within 1 Hz