On 3/21/23 8:50 AM, Eitan Tsur wrote:

Does anyone know of any currently-on-the-market NanoVNA hardware

revisions with MAX2870/MAX2871 PLL's? Seems like they have better
performance at higher frequencies than the ADF4350/4351, etc...
Considering single quantities for a MAX chip are ~$14 USD from Mouser, I'd
be willing to pay the money for a better performing model if software is
available to support the part.

Changing PLL is a major redesign of both hardware and firmware (that is,
it's not a pin for pin drop in). The MAX2870 only goes down to 23.5 MHz
which is fairly important for a lot of users. For that matter the
ADF4350 only goes down to 137.5 MHz

The register map is quite different between the parts.

The NanoVNA uses a Si5351 part which is a clock generator that goes 2.5
kHz to 200 MHz (it will actually go higher), and costs $2.44 in single
quantity.

The design of a VNA using either the MAX or ADF parts would be quite
different.

So it's not the parts cost that's the driver - it's the design cost -
And I'd expect that the parts cost on something covering microwave
frequencies to be substantially higher than the parts going into the
NanoVNA.

For example, you're going to need a better reference oscillator to go to
4 GHz, since the phase noise starts to be a bigger part of the noise
budget, and that 20log(N) bites pretty hard. You'll also need to deal
with layout and substrate issues - at 300 MHz, regular old FR4 works
pretty well, and the small variations don't make much difference (or
will calibrate out). Start getting up to 3-4 GHz and FR4 works, but
it's lossy, and the piece to piece variability gets bigger. Some
calibrates out, some doesn't.

All this can be solved in one way or another, but it's a fair amount of
work.

On 3/21/23 11:29 AM, Eitan Tsur wrote:

NanoVNA-F uses an ADF4350 already. Good point about register maps being
different, but the MAX and ADF are pin compatible last I checked

pins may have the same definitions, but is the supporting circuitry the
same.

FWIW, pin 16 on the MAX is Vcc-rf, and Vvco on the ADF. Vvco is pin 17
on the MAX. It's also Vvco on the ADF (it's on two pins)

Pin 19 is NOISE_FILT on MAX, TEMP compensation ADF.

So similar, but not the same.

The other difference, at first, is that RFoutA on the ADF is pulled up
to Vvco through inductors/chokes, while it's pulled up by resistors on
the MAX. Maybe the same would work, but it's a bit different.

The loop filter circuitry is a bit different, too - the MAX seems to
want a split in the resistor to ground, taken to SW (pin 6)

And it might want different values.

See LiteVNA64

No, LiteVNA use different board

LiteVNA contain SD card and RTC and use hardware i2c bus control
So V2 and Lite use equual VNA software but different hardware control

Yes possible build V2 firmware and add MAX2871 generator control, but you can`t just replace it, need also tune elements around it.
This all done in Lite

So most easy and low cost way order it (LiteVNA cost near 100$)