Assembly

All component values are marked on the pc board. The insertion and soldering of these components should be done carefully as with any good construction practices. Be sure to use a small tip soldering iron and good quality electronic solder. Make sure that you do not bridge connections with solder.

Assembly Tips:

The kit contents should be checked against the documentation provided. Color codes on the resistors should match the codes on the card and will show values if you question any value measure the component with a good ohm meter.

 All component values are marked on the printed circuit card.

 I find that it is easier to attach all small passive components to the card first. Then attach the IC socket (if used) and the Header and SIP 10-pin sockets.

Attach the Header sockets first and then the SIP-10 pin socket as it is easier to solder without the SIP pins in that way. I also find that if I attach the SMA connector as the first thing on the board, I can lay the board on a flat surface and make sure that the SMA connector is level with the board for correct position.

When preparing the Header pins, break one forty pin unit at the 10-pin length, the remaining 30 pin unit is trimmed to 8 pin length. The remaining piece is cut at 8-pins and the remaining length to 6 pins.

Use care when mounting the SIP 10-pin sockets, making sure that they are flat and straight for good alignment. Use the AD9520 for this, placing the SIP sockets into the module and then into the holes on the board. A good jig for alignment of the Header pins is the Uno itself. Insert the header strips into the Uno and place the PC card over them face side up for an exact alignment. Inserting the pins into your Uno this way, will keep them straight for future insertion. Tack solder end pins remove the unit from the Uno to complete soldering all pins.

Suggested Assembly Steps

These are the steps that I use to assemble the board.

1. Mount the SMA connector on the edge of the board, and solder, making sure that it is square and level.

2. Insert all resistors, solder and trim.

3. Insert all capacitors, solder, and trim.

4. Insert the transistors, solder, and trim. Insert the diodes, solder, and trim.

5. Mount the 8-pin IC socket.

6. Separate the header 40 pin strip in to 1- 10 pin, 2 -8-pin, and 1 -6 pin parts.

7.  Using the Arduino board insert the header pins into the Arduino sockets.

8. Place the Arduino flat pins up and lay the VAA board top side up over the pins.

9.  Solder the pins from the top of the board.

10. Remove the VAA board from the Arduino.

11. Insert the 2 SIP-10 pin sockets into the AD9850 as I did with the Arduino headers. They insert from the top of the board.

12. Turn the board over keeping the AD9850 flat on your table and solder.

13. Insert the IC into its socket.

14. Assembly Complete.

 

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Parts included in the kit.

 

Trim excess length from IC or socket flush with the board as it will provide better clearance to the power connector on your Arduino Uno

Parallel resistance option

 Most values of resistor may be 5% tolerance Your antenna system is designed to have a 50-ohm impedance, and bridge components should be as close to that value as possible, as the most accurate readings will occur when the bridge matches the impedance of the system being measured.

 I supply 51-ohm 1% resistors with my kits and have found this configuration to be very accurate. I also provide sockets marked for 100-ohm resistors as an alternative.

 To use this option; fill the positions marked for 100-ohm resistors and the places marked for 50-ohm resistors should be filled with 100-ohm units also, six positions total.

 Increased power  

 The AD9850 signal generator module generates about a 1-volt rf signal. The dual transistor 2N3904 amplifier provides an output of about 3.5 volts PTP.

 Since we depend on the measurement of small induced and reflective voltages our detector diodes must be of a low voltage drop device. Our original design without the transistor amplifier circuit required the use of an AA143 diode. A great device, but not easily obtainable in the U.S. The only source of these diodes was from England.

By increasing the power with amplification, we can use various germanium diodes such as the 1N34a, which are readily available and supplied with my parts kit. Of course, you may use the AA143 diode or optionally high-speed switching units such as 1N4143.  However, because of their various voltage drop configurations you may need to use a software smoothing function of the signal, provided by VAA.exe with these alternatives.