EB5AGV's Workbench: building my VNWA Kit
A pretty cool and handy gadget for RF work
This page is devoted to the construction of my VNWA 2.6 Kit designed by Tom DG8SAQ and distributed by SDR-kits
These are some of the characteristics of this VNA:
- USB-Powered and controlled Vector Network Analyser
- Works with WINDOWS 64 bits and 32 bits (Windows 7, Vista, XP, ME, 2000 and Windows 98)
- Coverage from 1 kHz to 500 MHz with dynamic range of up to 90dB. Useful performance up to 1.3 GHz with reduced dynamic range and accuracy
- S-Parameter: S11, S12, S21 & S22, VSWR
- Component Measurements: Resistance, Admittance, Capacitance, Inductance & Quality Factor (Q)
- Time domain & Gating in Time domain. Distance to Fault measurement
- Logarithmic and Linear sweep: up to 8192 points with sampling time adjustable from 0.2mS to 100mS
- Matching Tool and Complex Calculator. Crystal Parameter tool
- User defined S-parameter calculator
- Basic Spectrum Analyzer useful up to 100 MHz
- Dimensions: Width 10.4cm, Depth 8.0cm, Height 4.6cm, Weight 0.2kg
- Power requirement: USB 1.1 interface, 5V DC max 500mA
- TX-Out max RF Output as signal generator: -12dBm
- Max permissable external RF Input Level on TX-Out and RX-In ports: 0dBm (0.225V RMS)
- Connectors: 2x SMA, USB-B and USB-A
I got it at the end of 2010 from the last batch of kits available. Now you can only buy the unit assembled... I am not sure of the reason but, trust me, assembling this kit is not for the faint of heart!. Read on to know why...
Assembling the USB interface PCB
The original VNWA was interfaced via a PC parallel (LPT) port. That port is obsolete now so the designer decided to add a plug-in PCB to control the VNWA by a more common nowadays USB port.
So the first thing I did was to build the USB interface plug-in board. It has some SMD ICs but lots easier to deal with than the VNA PCB ones. All in all, here you have some pictures of the process.
The kit is beatifully packaged, as you can see here:
This is one of the SMD ICs being positioned prior to solder it
And this is the unit soldered... it is not as difficult as it may seem.
Hint: use soldering flux
This is the other SMD IC, already soldered:
A general view of the PCB:
And now more populated:
The rear side, with the interconnecting plugs:
Voila!
Assembling the VNWA PCB
OK, now that I had the easy circuit, I went for the real one!
This part of the kit is even more carefully packaged
This is the PCB with one of the SMA connectors temporarily placed
You need to file a bit the PCB in order to properly fit the connector
Assembly manual is nicely written and provides an step-by-step approach so you build a part, check it and then go for the next one.
This is first part, the main power supply
Then you add some more components and check they are OK
So far, so good... now, let's start with the dreaded DDSs!. No, my finger is not unusually large ;-). You can see how tiny these items are. And how many pins they have!
After some work, here you have first DDS placed
But... would it be soldered OK?. Let's use a magnifier...
It seems so!. OK, let's do the second one
I checked the DDSs, using the VNWA software and, yes, they worked fine!!!
So let's continue with next step, the output section
Once basically checked (only voltages and consumption), let's go with the input section:
So we are almost done!!!. And this is the result
Perhaps looking at the pictures it could seem a couple hours work... no, it took me lots more, because there are plenty of 0603 SMD components. And they are really small.
I wanted to do a good work, even with all SMD labels in same orientation and all soldering as nice as I was able to do. Here you have some detailed pictures
There is a semi-rigid coax which should be placed on the rear side
And then the SMA connectors... and this PCB is done!
Final assembling of the VNWA
Once I checked the unit, it was time to put it inside its casing
And this is the result of all the work, a little RF jewel!!!
Some measurement samples
Available soon... keep tuned!