The IP5303 inverter section is running at 350KHz when running off of the internal battery. That will create a pile of noise.
For a good sense of supply line noise, the IP5303 needs to be removed/disabled and a well filtered 5V linear supply used as Erik mentioned earlier.
That is why I suggested running off a 7.2V lithium pack, using a linear 5v regulator with low noise and transient specs.
The service manuals for various VNA analysers are all over the Web - have a look at how they filter their power sources.
A good source of manuals is:?
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On Friday, October 18, 2019, 3:16:34 a.m. GMT-4, erik@... <erik@...> wrote:
On Thu, Oct 17, 2019 at 01:02 PM, Dave Daniel wrote:
has anyone measured the +5 V rail(s) to see how noisy they are?
USB power is very noisy.
Hugen79 designed the power part of nanoVNA different from edy555
Hugen79 uses the output of the IP5303 for 5 volt where edy555 uses the USB power.
Did not check noise on IP5303 output but when the nanoVNA is running on internal battery noise is less so I assume its very high frequency noise coming from the USB VBUS, leaking through the IP5303
