Re: V2 and V3 roadmap
Jim,toggle quoted messageShow quoted text
Yes, there are sources of more or less random noise.
Filtering them out would improve performance.
But RBW is not a spec you typically see when a VNA is described.
I assume all these VNA's are using ADC's to digitize audio from a mixer
of the outgoing RF signal and a local RF signal that is perhaps 4khz away,
creating 4khz audio, to be digitized by an ADC. Should be able to reject
anything near that 4khz audio signal in the DSP firmware on the ARM.
Would need the two RF signals tightly locked to a common reference oscillator
to get stable 4khz audio at 6ghz.
However, there are other ways to implement a VNA.
I believe at least some of these new VNA's described by OwO
use the fundamental from the signal source throughout the range.
The original nanoVNA does use harmonics of the Si5351 to work above 300mhz.
The primary issue is that the fundamental is stronger than the signal of interest,
so the ADC needs more dynamic range to get the same margins.
Undesired harmonics (and the fundamental if over 300mhz) do not result in 4khz audio,
and are thus easily ignored.
So I doubt harmonics due to relatively small non-linearities in an amp would have much effect.
On Sat, Aug 22, 2020 at 11:28 AM, Jim Lux wrote: