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Hello,

Can the TinySA be connected to a USB power supply and operate directly off of the USB supply thus not discharging the internal battery or does the USB connection only provide power for charging?

Thank you.

On Thu, Jul 30, 2020 at 02:48 PM, @KC2TAU wrote:

Can the TinySA be connected to a USB power supply and operate directly off of the USB supply thus not discharging the internal battery or does the USB connection only provide power for charging?
===========================

? ?If you are familiar with the NanoVNA, then the tinySA is powered similarly.? If not, then yes the tinySA can operate off either USB power or the internal battery.? The tinySA USB port is used for charging, powering and for communications with a PC.

? ?When connected to a PC with an active USB port, charging occurs whether the tinySA is powered on or off.? My beta tinySA did not have a battery installed and I was able to operate it from my PC's USB port or from an ac or portable USB charger.

- Herb

Herb,

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.?

?

Thanks

?

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

Indeed, all power regulation is linear. NO switch mode supplies inside the tinySA
The biggest source of disturbance is the 30MHz TXCO inside the LO can causing 30MHz harmonics on the high input.
The disturbances in the low input mode are caused by FM,DAB Mobile phone and other nearby transmitters that blast through the tinySA shielding.

Is it worth lining the sandwich pcb which is in lieu of a case on many of the units with conductive sticky tape such as used inside some cellphone plastic cases? I understand that this stuff is better than extra solid metal screening as it absorbs, rather than reflecting some signal back into the circuitry.

I have just ordered a roll from Fleabay and am waiting for my TinySA to arrive.

Steve, G7psz

Putting absorbing tape at the inside of the shieldings may help, in particular for the high input shield as this may reduce the TXCO harmonics.