Part Five – The G5RV – A Complicated Antenna Disguised As A “Simple” Dipole
Well, rather than get into a another major variety of antennas on this installment, I thought I might address a specific antenna that has received a lot of good and poor reviews over the years – the G5RV!
This was invented (and promoted) by Louis Varney, G5RV/SK way back in 1946. It left such an impression on the Amateur Radio Community that it has taken on the name of its creator’s call sign. Mr. Varney has shuffled off this mortal coil back in 2000, at the age of 89. Surprisingly, after his demise some Hams made a pilgrimage to Mr. Varney’s Antenna Farm. It was, reportedly, full of all manner of antennas, but not a single example of his classic G5RV Antenna! I don’t know if he had tinkered with it enough over the previous 50 odd years, or he was not as much a fan of this design as some might think?
A quick description for a G5RV antenna would be a 102 foot long dipole, fed with open line transmission line of a specific length (depending on the type of open line is used), connected to a coaxial cable, which would then be connected to an antenna tuner. G5RV’s are multi-band antennas described as usable from 80 to 10 meters with a better take off angle on some bands than on other bands. Some designs recommend baluns, some do not!
The dipole portion is relatively straightforward – the higher the better, it can be horizontal or can be installed as an inverted “V”, but most authors caution that its angle should be 120 degrees or greater. Some people crumple up the dipole’s ends, but others discourage this compromise. Why 102 feet? That would be resonant somewhere around 4.72MHz!? Well, your basic dipole is not only resonant at half wavelengths – it will be resonant at any odd multiple of ½ wavelength, i.e. ½ λ , 3/2 λ , 5/2 λ, etc. The G5RV is designed with a dipole length cut for resonant 3/2 λ at 14.150Hz, and most G5RV owners are happy with their 20 meter operation.
The open wire segment is almost black magic – if real open wire is used, it should be cut to 34 feet long, if ladder line is chosen (with an impedance of 450 ohms) it should be cut to 30.6 feet long, and if television twin line (with an impedance of 300 ohms) is used, it should be cut to 28 feet. Keep in mind that although open line has very little loss, it is very sensitive to any metallic objects nearby. Lay it against your metal gutters and your antenna might screw the pooch! Some people offer other length suggestions!
The coaxial cable attached is black magic too. Some suggest that its length is unimportant, while others swear that its length makes an incredible difference in its capabilities. Then you have to research if baluns are beneficial or detrimental and where they might best be placed. Be ready with a sturdy antenna tuner that can handle a 10:1 SWR or you might be out of luck trying to tune some bands.
For those that can’t manage a 102 foot dipole there is a variant, called a G5RV Jr., which uses a 51 foot dipole instead. The junior variant is supposed to cover 7 to 28 MHz. It’s another compromise, heaped upon a compromise antenna. Your mileage might vary…
So… how does it really work? Damned if I can be sure. The guys that run antenna simulation software for fun are often heard very loudly arguing what is really going on, to make a G5RV work on so many different bands, and why it may not work so very well with all those bands. The obvious explanation is that it is a much more complicated design than it looks to be. You obviously have the 102 foot dipole, then there is the feed-stub of the open wire transmission line AND the coaxial transmission line. Some pundits suggest that portions of the feed-stubs act as radiating portions of the antenna! That’s why putting an RF choke style balun can foul up this characteristic. There are many fine articles on the Internet that discuss how each band uses a different antenna mode to do its magic. Many contradict each other, so I leave it as an exercise for the reader to Google the subject and find a description that they favor.
The G5RV was the miracle antenna of the late 1990’s and early 2000’s – they were many newbie Ham’s first serious antenna (as opposed to a piece of random wire thrown out the back window). The Amateur Radio community has grown more disenchanted with the design in recent years. It’s a bit of a crap shoot, if you will. If you get all the wire lengths right and they work for your location it can be a great compromise antenna. If one of these factors is off, you’re stuck with a lemon. As Clint Eastwood has been known to say on The Silver Screen:
“…you’ve gotta ask yourself one question: “Do I feel lucky?” Well, do ya, punk?”
Well, Einstein suggested that he didn’t think that “God plays dice with the world…”
Well, I wouldn’t play dice with my antenna system, but it’s a free country – you decide!
So, that’s it for the (in)famous G5RV – some Hams swear by them, others swear at them!
On to the next topic for next month’s installment!
-The Editor- (I can be contacted at TheEditor@KCRC.com)