A series of four articles explored different wireless solutions for remote operation of a NanoVNA-H4.
The NanoVNA-H4 can use a USB connection, or a serial connection, the UART, selected from the configuration menu. The UART ‘channel’ is a conventional unprotected asynchronous protocol, 8N1, and supports a range of DTE speeds.
Three different wireless remote solutions were trialed, and an inexpensive Bluetooth adapter showed the most promise. The air-link is a ‘reliable’ link in terms of error free transmission, though of course it depends on adequate signal strength. Importantly, even at 115200bps DTE speed, it did not seem to suffer buffer overruns, an important detail given the lack of effective flow control in the NanoVNA-H4 UART interface (as brought to the edge pads).
In response to the need for a more efficient data transfer for screenshots (~399kB), Dislord has released a version of NanoVNA-D that supports a RLE compressed screenshot download.
The Python script published at https://github.com/owenduffy/tinydevicecapture allows standalone screenshot capture using the new “capture rle” command which permits screenshot download in 2-5s at DTE speed 115200, less than a quarter the uncompressed image.
Above, a loopback throughput test at 20m outside gave throughput of 42958bps, so it is deemed prudent to configure the NanoVNA serial speed to 38400 bps to minimise the risk of buffer overruns. Transfer time for a not very busy screen is around 6s.