Monday, 11 December 2017

The FA-VA4 Vector Antenna Analyzer (LF-100MHz)

For some time I had been considering the purchase of the MFJ259 antenna analyzer but after a little online sleuthing, came across this little beauty, the FA-VA4 Antenna Analyzer by Funk Amateur in Germany and available through their Box73 website here.

I liked the fact that the cost of the analyzer was about half that of anything else comparable ($140 US including shipping) and that it covered the new 2200 / 630m bands!

I think many amateurs planning on building a system for either of these new bands will find the very affordable FA-VA4 a handy piece of equipment when it comes to working on their LF / MF antenna since most available SWR meters do not cover these frequencies accurately.

Delivery time was fast and everything was very well packaged. The FA-VA4 comes in partial kit form and requires only a short amount of time to put together.

The necessary assembly consists of soldering pin strip connectors, switches, AA cell holders, and the BNC connector. All of the tricky SMD components have been pre-mounted ... total assembly time was less than 60 minutes and everything fired-up nicely, without problems, thanks to the well written instruction / user manual.

Included with the kit are three BNC connectors needed to calibrate the instrument for the highest accuracy. These consist of a 'Shorted' connector, an 'Open' connector and a 50 ohm 'Load' connector (SOL). A simple three-part calibration procedure for all frequencies takes about 15 minute to complete, while the instrument calibrates itself as it scans through all frequency ranges with each connector plugged into the output. Once this task is completed, the analyzer is ready for use.

If you're like me, I think the main use will be to check out and tweak some of your HF antennas using the SWR or Z sweep function. This allows you to set a desired 'center' frequency along with a + / - sweep range and have the display draw a nice plot of your system.

Had my 630m antenna not already been tuned and matched, I would have found the analyzer to be a great help but, thanks to my 'scopematch', that antenna has already been optimised.

All menu features and data entry is via three momentary-contact push switches. Although this might initially seem awkward, it is not, and operation is pretty intuitive.

The main modes of operation are:

Single Frequency SWR  Measurement


Single Frequency Impedance Measurement


Single SWR Measurement Run


Single Run For Impedance Measurement (Resistance and Reactance)


SWR Measurement On Five Frequencies (5 Band Measurement)


As well, all of the above can be viewed in a continuous 'cycle' mode, as inputs are changed and all screens can be saved for future reference.

Additional capabilities include use in an HF Signal Generator Mode (~ 1V square wave @50 ohms), the ability to measure C and L at a given frequency, as a 'dip meter' and to measure cable resonances and determine lengths.

The complete manual may also be downloaded from their website here.

I will soon put all of my antennas to the test and see what work might need to be done to optimize them, particularly my HF half slopers, which, in spite of their great performance, have always proven a bit of a mystery when it comes to pruning them to resonance ... I rather suspect that the sloping wires are more of an impedance tuning stub than a radiator and that most radiation comes from the vertical support tower, not the sloping wire.

All-in-all, the FA-VA4 appears to offer very good value for the money and is a well built, quality test instrument. I think it will become a popular choice among hams, especially those on LF / MF. The only thing different that I would have liked, would be to have a UHF (SO 239) connector rather than a BNC on the output, since most amateurs are using these on their HF systems ... or, the inclusion of a BNC-to-UHF adapter.

If you already use this device, please feel free to add your comments below!


Dan Romanchik said...

I recently also built one of these, and I think they're a great deal, too. I sold my Palstar ZM-30 because I'm so happy with this unit. It's certainly much lighter than the Palstar, so that should make it easier to use out in the field.

I wish they would have used an Arduino-compatible processor, so it could be hacked on a little bit, but that's not a big deal.

73, Dan KB6NU

Steve McDonald said...

Glad to hear positive comments Dan. At this price it should be very popular.

Photon said...

Thanks for the intersting post.

That's going to be very popular, given its price and the ability to provide both magnitude and sign of the imaginary part of impedance.

The display seems almost indentical in type,if not detail, to the 'legacy' RigExpert analysers.

One can only hope that the unjustifiably-high price of much of our equipment is reduced as technology and kits spread - and become accessible to those not on a golden post-war pension!

Ken said...

Very interesting. Neat little unit. If it does resistance and signed reactance that can be useful. Signed meaning showing plus or minus reactance. Useful for experimenting or even saving time with antenna issue. The You kits just shows impedance (Z). Impedance (Z) is resistance + reactance. The MFJ has those features and maybe a few more. I guess that's why I held on to it.

You can put a low band antenna on a car (as a good example) and have it resonate and dip perfectly on frequency. But have a 2 to 1 SWR because the impedance is 25 ohms. Breaking out the reactive components can help with a solution.