On Thu, Jul 30, 2020 at 08:16 PM, Larry Rothman wrote:
Herb,
?
Erik said the unit uses an analog power supply to eliminate noise when plugged into a usb port.?
?
Does it now use a low dropout 3v reg directly off the Li battery? The only schematic is for the RF side so I'm curious about the supply section.?
?
Hi Larry,
? ?Erik has said he will only release portions of the schematic as needed by users to troubleshoot any failures with there devices.? I believe that is a wise choice after witnessing how quickly clones of the NanoVNA-F and SAA-2 hit the market.? The latest version 3.x of the NanoVNA-F also will not release full schematics and the SAA-2 producers are wishing a little late they had not done so.
? ?My pre-production tinySA has been working so well I hesitate to open the case until the production level unit I ordered arrives.? I can say that I have operated the tinySA from usb power and disconnected from the PC on battery power, at the lowest 3kHz rbw I can see down -100dBm or better from either source. Almost all internally generated noise is leakage from the LO.? Using a 3kHz rbw and a wide span, the sweep time is in the seconds, but if you need to measure down to -100dBm ...
? I did look back through my notes and Erik wrote the following:
The tinySA power supply circuit is linear (no switched power supply)? using LDO regulators directly from the battery. Separate regulator for RF part. L/C filter to eliminate regulator noise.?
After Eriks's experience with switched power supply noise as a user of the original NanoVNA, his use of a linear regulator in the tinySA is not a surprise.? He also reserved at spot on the PCB for a huge Vdd-RF capacitor (C53) that can be added later if it becomes required.
- Herb
