HF Arduino Vna (english version)

By F4GOH

The main characteristics of Vna analyzer are:

• HF : 1 MHz à 60MHz
• Reflection and transmission analysis
• Uses the DL2SBA Jvna software
• Mode « Standalone »
• LCD display 4 × 20
• Bluetooth with Blue VNA Androïd software
• Scrolling menu by rotary encoder
• Cost € 50 without Bluetooth Module

The VNA is based on the following components:

• Arduino NANO
• Module ad9851
• ad8302

ebay-links : components list

Pcb available mail me :  f4goh@orange.fr
Introduction :

This HF VNA is an adaptation of the scheme described in the Russian site RA4NAL. I use an Arduino Nano and system measurement on the same board. I add rotary encoder and lcd display to use the VNA in standalone mode. The PC software is Jvna same as miniVna from  DL2SBA.

you can use the VNA from 3 differents software interfaces:

Mode 1: Connect to PC

The VNA is connected to Arduino nano via miniUSB. The PC software is Jvna same as miniVna from DL2SBA (http://vnaj.dl2sba.com).
It is possible to analyse antennas in reflection mode or filter in transmission mode.

Mode 2: Connect via Bluetooth Module

The VNA is connected to via Bluetooth Module. Using blue VNA software, it is possible to analyze antenna like on PC computer, except you can up the VNA on the top of your pylon.
you can then perform analysis without cable.
(https://play.google.com/store/apps/details?id=ro.yo3ggx.btvna&hl=fr)

Using Mode 3 in « Standalone ». Just a 5V power supply to operate all. With mSd Card inserted, all measurements is saved in a text file. It can be possible to anayse them on a spreadsheet.

The information of antenna parameters are displayed on a 4 x 20 character LCD screen. The selection of the band or frequency is done with a rotary encoder.
the handling is quick and has few menus.

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Main board description :

V2 schematics

We can easily recognize the RA4NAL scheme, the Arduino UNO was replaced by a NANO facilitating the integration of the USB connection.

The AD9851 DDS is an oscillator, the signal is amplified by an ERA2SM and attenuated by R25,R26,R27 before attacking the tandem coupler based on a BN43-202.

The direct and reflected power of the coupler is attenuated by a couple of T Résistors and  injected into a ad8302
The ad8302 will give us a DC voltage proportional to the magnitude and phase of the two signals.

These two voltages Vmag Vphs and are converted into an average of 20 digital values by the Arduino.

In PC software mode , these numericals values is directly transferred into Jvna software. Jvna compute all antenna parameters like RL, |Z|, |XS|, theta, swr.

SPI connection is shared between the DDS and the MSD card. Knowing that the power supply of the MSD card is 3.3V, it will add tension divider to Arduino.

The LCD display 24 × 20 characters is controlled via the I2C bus provided that it is equipped with a PCF8574 interface (I2C Serial Interface Module For LCD1602 Display).

Beware to use an bluetooth module (connected on J7) is compatible 5V level I / O, because this is not the case for all modules.

If you wish to scan with Jvna software on PC, you must disconnect the Bluetooth module in order not to provoke conflict on the serial line.

The LED D3 lights when there is a data transfert on the serial line.

Omron relay allows to activate the mode of transmission and thus measure the gain of a filter interposed between the DUT output and input DET.

If you want to use mSD card, you must load VnaArduinoSd.ino into Arduinonano, and install Arduino sdfat library. Insert your mSDcard into a module and connect it to J3.

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Soldering and testing:

Start with soldering the support of the Arduino Nano, support for the AD9851 DDS, the connector of the LCD display and rotary encoder. (rotary.png)

Do not forget the decoupling capacitors and anti-bounce. (C12, C18, C20, C21)

VnArduino.ino program the file in Arduino from the following link:

https://github.com/f4goh/VnArduino

Use xloader if you want to upload firmware without compilation

Hold the rotary encoder button for switching on to access the menu.

From the menu, choose JVNA

Once validated, then the Arduino reset itself into JVna mode

Start Jvna on your computer, choose the correct COM port in the « driver selection » menu and « miniVNA ». Make a connection test and click update.

Perform a phony reflection calibration for now, then in the frequency calibration menu adjust the DDS ticks 23,860,477 to be compatible with the AD9851.

Go into the GENERATOR menu, click « on air », then check the frequency generated with an oscilloscope on the DDS output. (10Mhz) Adjust ticks to obtain 10Mhz with a frequency counter.

Solder now the ERA-2SM amplifier or an equivalent component of your stock.

Recheck the output signal of the amplifier with an oscilloscope

Now weld the measuring bridge (tandem coupler) and the T attenuators.

The tandem coupler used to measure the direct and reflected powers is made with a binocular toroid BN-43-202 (2×5 turns, 0.5MM)

On 50 ohm load, check with an oscilloscope the voltages across R12 (max forward voltage) and the terminals of R6 (reflected voltage near zero).

Without load (open output), with an oscilloscope check the voltages across R12 (max forward voltage) and the terminals of R6 (max reflected voltage).

Finish by weld the components around the ad8302.

Check with a voltmeter the reference voltage VREF supplied by ad8302 to be 1.8V.

The VNA is ready for use.

Repeat calibration, this should match the screenshot below.

To use the « standalone » mode, it will be necessary to perform a calibration (menu on the 4th line of the LCD display).

The location of calib resistors are used to adjust the load on measurement for 50ohms RS = 50 ohm.

It is then necessary to place a single resistor with a value between 300ohms and 2Kohms on one of the two sites, but perhaps only will you not need.

73 and good parts assembly

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Improvement of the measurement by F1AIA:

Below the diagrams containing the changes to be applied at the level of attenuation values as well as the amplification part with the replacement of a ERA to SGA3386. By applying these corrections, you can be measured attenuations to -40dB and S11 values or Return Loss (RL) -35 to-39dB.
The dynamics of the whole is enhanced with better amplification of SGA, accompanied by a better choice of reference values applied to the inputs of the AD8302.

Jean-Claude thank you for this info.

SGA3386 with his 68 ohms resistor

DET attenuation correction

V3 schematics

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OZ6HR Edition

• Choose U2 or U4 depend of ad9851 pad(if you use U2 put a strap on J10 (2-3)
• For card reader  choose J3 or J9 depend of sd reader (if you use J9 do not put R16 to R21and R10 resistors)

Update file on github for special OZ6HR edition

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Congratulation Rainer (OE1KFR)

Thanks to YL2GVC for his picture, great !

Russ K0WFS VNA

Russ K0WFS VNA

Luca I6QIZ

Luca I6QIZ

Ray m0dhp