Herb,
Actually, two different odd harmonics get used.
From Erik's post of
/g/nanovna-users/message/1743You are explaining well, except the SW uses above 300MHz the 3rd harmonic of one clock and the 5th harmonic
of the other clock to avoid detecting the 3rd harmonic of the mixing product of the 1st harmonics of the clock's
Example 200MHz + 200.00166MHz produce from 1st harmonic 1.66kHz which will include a certain amount of 3rd harmonic at 5kHz.
Using 200MHz + 120.001MHz produces only 5kHz when their 3rd and 5th harmonic combine
Also, the Si5351 is spec'd to operate at up to 225 mhz, anything beyond that is a gift.
Those for which the PLL craps out at 290 mhz are not necessarily from "shady sources".
Perhaps just cut from the outside edge of the wafer, but still perfectly compliant with the spec.
Jerry, KE7ER
On Fri, Jan 17, 2020 at 09:20 AM, hwalker wrote:
On Fri, Jan 17, 2020 at 07:49 AM, <nanovnagroup@...> wrote:
From the link at the Wiki section:
It states that top frequency range is 900MHz:
========================================================
It actually states that third harmonic operation is 300-900MHz. The fifth
harmonic is used for 900-1500 MHz operation. This is a basic principal of
operation for the NanoVNA that should be well understood by most user's. I
would think that would be especially true if the user's the name is
"nanovnagroup" :)
As Larry replied, some NanoVNAs will only able to reliably achieve 266.7-800
MHz third harmonic operation, and 800 - 1.300 MHz fifth harmonic operation.
Hugen specs his v3.4 NanoVNA-H as operating reliably to 1.5 GHZ. His v3.4
board uses the same synthesizer chip as his original NanoVNA-H so I'm guessing
he must be cherry picking his synthesizer chips. Think of it as overclocking
your PC's clock, the majority of legitimate chips will operate reliably pass
their marked frequency, but those using seconds from shady sources probably
will not.
- Herb
