You may also find this tutorial about the Si5351A on the RFzero site
useful: It explains the
frequency generation process more clearly than the Silicon Labs application
note does, and guides you through the process of choosing appropriate
settings for the chip. The site also has code.
toggle quoted message
Show quoted text
On Tue, Jul 28, 2020 at 9:18 AM Jim Lux <jimlux@...> wrote:
On 7/27/20 11:38 PM, Rudolf Schaffer wrote:
Brandon, that's exactly what i was asking for !
I've read the Si5351 datasheet but don't find an answer.
The data sheet doesn't give the details of the PLL or other synthesizers.
SiLabs has a free program called ClockBuilder that figures out how to
program it, using your desired frequencies.
What you want is this:
which gives the equations for the PLL, Multisynth, and final dividers
foutx = fvco/(Output multisynthx * Rx)
fvco = fin * Feedback_Multisynth
Valid Multisynth divider ratios are 4, 6, 8, and any fractional value
between 8 + 1/1,048,575 and 2048.
fvco = fxtal * (A + B/C)
Thank you for your message.
Rudi
Le 27.07.2020 ¨¤ 22:34, Brandon Swift a ¨¦crit :
Rudi, I think I understood your question from your first message, and
your second message did make it more clear.
For others, I think Rudi is asking "what is the smallest amount we can
increment the low-level generated tone? (and this seems to vary with
frequency)". I don't think he's asking "how do I find the step size in
the VNA sweep?"
I believe the answer ought to lie in the datasheet of the Si5351A
clock generator, the main signal source of the NanoVNA
However, I can't find that info in that datasheet right now, and can't
look at control source code effectively. Maybe someone more familiar
with the ins-and-outs of the Si5351 can provide some more insight?
On Mon, Jul 27, 2020 at 12:11 PM David Eckhardt
<davearea51a@...> wrote:
Moderators, please,....PLEASE.....place this in the Wiki as this is the
third time I've explained this.
Dave - W ?LEV
On Mon, Jul 27, 2020 at 7:10 PM David Eckhardt <davearea51a@...>
wrote:
Frequency step between measured points has more to do with FREQUENCY
SWEEP
WIDTH than absolute frequency, itself. The native NANO's offer 101
measured steps over any specified frequency sweep. So a general
formula
which gives the measured point spacing during both for cal and
measurement
is:
FS = (Upper Frequency - Lower Frequency) / 101
Where FS = Frequency Step or Frequency Spacing
A couple of examples might illustrate this. Assume one wishes to
look at
an antenna over the entire 75/80-meter band, 3.5 to 4.0 MHz. The
frequency
spacing or frequency step would then be:
FS = (4.0 MHz - 3.5 MHz) / 101 = 4.95 E-3 MHz or 4.95 kHz.
A measurement, both in cal and measurement, would be made every 4.95
kHz.
If measurement of SWR is the goal, this spacing should be adequate to
assess the fine structure of SWR behavior over the entire
75/80-meter band.
Now, assume one desires to measure an antenna over the entire 70-cm
band,
430 to 450 MHz. In this case, 200 kHz spacing between measured
points may
not be adequate to assess the fine structure of the SWR behavior
over the
entire 70-cm band.
FS = (450 MHz - 430 MHz) / 101 = 1.98 E-3 MHz or
roughly
every 200 kHz.
However, using NANOSAVER on a PC or laptop, up to 10 'segments',
each of
101 measured points can be made. One need just specify the number of
segments to obtain better resolution.
For example, if one specifies 5 segments over the entire 70-cm band,
this
would yield a measurement point spacing of:
FS = ([Upper Frequency - Lower Frequency] / 5) / 101 =
([450 MHz
- 430 MHz] / 5) / 101 =39.6 MHz or roughly every 40 kHz.
This should be adequate to assess the antenna over the entire 70-cm
band.
Dave - W?LEV
On Mon, Jul 27, 2020 at 7:46 AM Rudolf Schaffer <
rudolf.schaffer@...> wrote:
Hello,
Can somebody explain to me how to define/calculate the minimum
frequency
step versus output frequency for a NanoVNA-H4 ?
Thank you in advance.
Rudi
--
*Dave - W?LEV*
*Just Let Darwin Work*
--
*Dave - W?LEV*
*Just Let Darwin Work*
Shirley Dulcey KE1L