VSWR what?!

In the December 2013 edition of Kitplanes magazine I found yet another useful piece of information, and like so many other times during this build, it came a year or so too late. The article was written by Jim Weir–maker of many canard antennas–and discussed checking the VSWR (Voltage Standing Wave Ratio) of each antenna before burying it under the skin of a plastic airplane such as the Long-EZ, at which point if you have a problem . . . well, better think up some good solutions!

Jim recommended a MFJ-259B Antenna Analyzer to check the VSWR on each antenna to ensure they were good.  Again, my antennas already being installed, I still wanted to check them to A) know if any had a VSWR too high to count as good, and B) pick the best between the COM antennas for COM1, and the best between the NAV antennas for NAV1.  The goal is a VSWR ratio less than 3:1, because anything higher is a lot electrical energy traveling back along the OUTSIDE of your antenna coax cable to the transmitting device (ie, radio), which will drive your available Tx wattage to unacceptably low levels and could damage your transmitter in the process.  In addition, as with so many other units of measurement in the weird & wonderful world of electrons, VSWR readings are logarithmic.  Any increases above a 1.5:1-to-2:1 ratio and things start getting real hairy real quick!

I of course started hunting around for a good, used antenna analyzer at an acceptable price anywhere I could find one.  That pretty much drove me to eBay, where I picked one up for about half the price of a new one.  And thar she be below.

MFJ-259B Antenna Analyzer

The only problem with my newly won prize (which I actually bought a while ago), was the antenna cable adapter that came with it.  These analyzers can be used for checking any antenna and are common in the HAM radio world, so perhaps the antenna cable adapter that came was used for something even more exotic by a HAM radio bubba.

Old Connector ???So although I didn’t know what the mystery adapter was used for, I did know that to check the BNC connectors used on the Long-EZ antenna cables that I would need a BNC adapter for the antenna analyzer.  So, last week I ordered a couple of them, one male and one female, and I got them in today.

New BNC connectors M & F

You can see the new BNC antenna cable adapters on the right, and the old one on the left. Below is a shot of one installed on the antenna analyzer.

It fits!

Since the weather is still too cold to economically heat my workshop for glassing, I plan on terminating all my antenna cables with BNC connectors and then checking the VSWR of each one with this MFJ-259B antenna analyzer.

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