nanoVNA-H – recovery

This article applies to the original NanoVNA (v1) by edy555 / ttrftech, and the NanoVNA-H derivative.

I often see reports that a nanoVNA has been ‘bricked’. The term seems to have become part of the vernacular of would be pros. The term ‘bricked’ certainly applies to electronics that can no longer be programmed through ‘ordinary means’ and is to all intents and purposes as useful as brick, but in most cases, the nanoVNA is recoverable.

The STM32F072 chip  used on the original nanoVNA has some features that make the firmware update process simple and robust, and difficult to mess up.

The normal way of doing a firmware update is using the DFU protocol from a PC over the USB interface. To use this, the device has to be “put into DFU mode”, this means that the chip is reset and started executing the bootloader in permanent system memory.

The concept of DFU is that normal client programs used with the device can easily be extended to include the DFU function as just another menu function of the client software. NanoVNA-App does this, but in my experience most PC client programs do not.

So, you probably need to use a programming client, and for Windows a good choice is ST’s DfuSeDemo. You may need to convert the distributed file format using Dfu file manager from the same distribution, not all developers distribute a .dfu file.

There is a pin on the board, BOOT0, that must be held high during reset to enter the on-chip bootloader. Later firmware versions also provide a menu option to enter the bootloader, but if an attempted upgrade messes up the menu, you may need to use the BOOT0 pin bridged to the adjacent VDD pin while you power cycle the nanovna.

Some later hardware can be booted in DFU mode by pressing the jog button in while powering on.

Above is the rear view of the board, and a jumper using pogo pins to bridge BOOT0 to VDD. Continue reading nanoVNA-H – recovery

nanoVNA-H – rework of v3.3 PCB to v3.4?

nanoVNA-H v3.4 is out, and I don’t yet see significant problem reports.

When I compare the circuit with v3.3 (which I have), apart from new battery charger IC etc, the changes are in three areas:

  1. decoupling power to the mixers;
  2. increasing the drive to the mixers; and
  3. higher attenuation of input on the rx port. Continue reading nanoVNA-H – rework of v3.3 PCB to v3.4?

nanoVNA-H – v3.3 USB problems

At nanoVNA – measurement of two 920MHz LoRa antennas I mentioned my growing frustration with the USB interface on the nanovna, particularly the tendency to reset the nanoVNA with the slightest wiggle and the frustration in trying to use the resulting mess.

I have previously cleaned both plug and socket a couple of times, the last time was after some board modifications and flux residue was washed from the board keeping the USB socket dry, then the USB socket was flushed with clean solvent and blow dry.

The USB problems have become apparent only recently and rapidly got worse. Continue reading nanoVNA-H – v3.3 USB problems

nanoVNA – that demo board and its U.FL connectors

One of the many nanoVNA cloners makes an interesting little inexpensive demo board with a selection of components, filters etc to develop familiarity with the nanovna.

Above is a pic of the demo board and the supplied jumper cables. The demo board may not include information relevant to using the cables and connectors supplied. Continue reading nanoVNA – that demo board and its U.FL connectors

nanoVNA user post provides an interesting example for study #1

At https://groups.io/g/nanovna-users/message/9185 a user posted a measurement made with his nanoVNA of a length of coax with termination.

Above is his initial reported measurement of an approximate 350′ length of coax with a known good dummy load on the opposite end. 350′ is 106.7m. Whilst this chart is less value than a Smith chart rendering, understanding the nature of things allows us to infer the Smith chart. Continue reading nanoVNA user post provides an interesting example for study #1

nanoVNA-H – measure 144MHz Yagi gain – planning / feasibility

This article documents a feasibility study of using the modified nanoVNA-H to measure the gain of a 4 element 144MHz Yagi, the DUT.

The intended configuration is the DUT will be connected to the tx port (Port 1 or CH0 in nanoVNA speak), and a known ‘sense’ antenna connected to its rx port (Port 2 or CH1 in nanoVNA speak).

nanoVNA |s21| noise floor

To make useful measurements of the received signal, the rx signal level must be a reasonable amount higher than the noise floor, 10dB should be sufficient.

Above is a plot of the |s21| noise floor around 146MHz. Continue reading nanoVNA-H – measure 144MHz Yagi gain – planning / feasibility

nanoVNA-H – measure 40m low pass filter for WSPRlite flex

This article demonstrates the use of a nanoVNA-H to measure the response of a low pass filter designed to pass 7MHz frequencies but attenuate harmonics. The inductors and capacitors make a seven element Chebyshev filter as designed by G3CWI for use in a 50Ω system.

Implementation

Above, the filter is assembled on a piece of matrix board with two BNC connectors. The inductors are fixed with hot melt adhesive, and the whole thing served over with heatshrink tube. It is not waterproof. Continue reading nanoVNA-H – measure 40m low pass filter for WSPRlite flex

Antennas – disturbing the thing being measured – open wire lines

A common question in online forums relates to inability to reconcile analyser measurements of an antenna system with the transmitter system antenna facing VSWR meter.

The cause is often that the antenna system was changed significantly to connect the analyser.

Seeing recent discussion by the online experts of how the measure the impedance of an antenna system looking into a so-called balanced feed line gives advice that is likely to cause reconciliation failure.

I will make the point firstly that the line is not intrinsically balanced, it is the way the it is used that may or may not achieve balance of some type. I will refer to that type of line as open wire line.

Let’s explore the subject using some NEC models.

I have constructed an NEC-4.2 model of an approximately half wave dipole at 7MHz, it is 20m above the ground, and fed slightly off centre with open wire line constructed using GW elements. At the bottom, I have connected a 2 segment wire between the feed line ends, and two sources in series. Continue reading Antennas – disturbing the thing being measured – open wire lines

nanoVNA – a surfit of choices

An oft cited advantage of the nanoVNA are choices:

  • hardware (several clones of the basic thing, the ‘improved’ -H series, the coming -H with bigger screen, the -F with bigger screen… and the future v2);
  • firmware (lots and lots of forks, some hardware targeted);
  • external clients (PC clients, web interfaces, Python / Octave / Matlab code etc).

There is not necessarily interoperatibilty between all instances of each level of this tree. For example, nanovna-F may not share firmware images with the original nanoVNA and its clones, and vice versa due to a different display protocol.

Some PC clients support features not implemented in all current firmware versions, eg screen capture. Continue reading nanoVNA – a surfit of choices