My friend Don “Skip” Trueman, VE4AY, sent along this article about his home brew G5RV antenna.
“I made up a G5RV antenna using stranded drawn copper wire for the dipole and the open wire feed-line. This was ordered up from where I forget, but 4 packages of 50 feet each came in the mail. It’s about 18 gauge wire. It seems that whoever cuts it up and packages the wire isn’t
reliable about that 50 foot thing, as one length worked out to be about 5 feet short…however, having extra from the feed-line requirements, I spliced in the missing difference. The other half was nicely longer by about a foot, so the dipole looks textbook for dimensions on 20 meters. I could have checked the other packages for length and saved the splicing but I didn’t need 4 runs of wire to fuss with, one at a time is plenty!
There are two ways to deal with the feed-line. One uses about 35 feet of open wire line which goes to a coaxial line to get from outdoors to indoors where presumably, you connect a matching network. Arguably this will only work on 20 meters. The other approach is to put the matching network outdoors and use coax in a more conventional way, transmitter to matching network with a reflected power meter at the
operating position. This can work on any band and this was my preference for the G5RV antenna.
I made the transmission line (feeders) with 1/8 inch plexiglas (plex) spacers, one inch by three inches, spaced on the line at about 18 ins. Each is 3 inches wide to separate the feed-line wires. I put a notch in the end of the spreaders and a hole through the spreader just in from the notch. The feed-line wire fits in the notch and a short piece of enameled wire is inserted through the hole and wrapped around the feed-line wire to keep it in the notch. The transmission line is approximately 500 ohms based on the spacing between the wires. It does not match the feedpoint impedance at the antenna. It is a mismatch, but the losses are very, very low when the system is “matched”. A coaxial feed would work on 20 meters and probably show a reasonable match, but only on 20 meters. The antenna would likely be unusable on any other band.
G5RV Antenna Matching Network
Now to the matching network for the G5RV antenna. Over the years, the late Lou McCoy (W1ICP) wrote several pieces on matching networks in QST periodicals. (1)
I used a variation of one of these to match the open-wire line from my 50 ohm feed. I built a weather-proof box from an aluminum chassis and a plex cover. The plex cover allowed me to adjust matches and close it up with out “retuning/detuning” the match. Coaxial (SO239) in and two
ceramic feed-through insulators for the feed-line. The network can be configured as series or parallel to achieve a match on any band. The G5RV is a 20 meter antenna and presents some interesting characteristics when used on other bands…so that matching network gets put to good
use!
My equipment is set up in the basement of my home, and the matching network is outdoors and around the corner. Tuning up was quite a lot of exercise! I put a reflected power meter at the input to the network and a brick on the key (about 10 watts to the mismatch) and adjusted the network for no reflected power on the 5 major bands. Logged the settings with calibrated knobs and coil clips with alligator jumpers for band changes…out of curiosity, I reversed the feed-lines on the terminals and there was no change to the network tuning. Also, twisting the line 180 degrees as it came to the match had no impact on the noise level. A second reflected power meter at the operating position also showed the absence of reflected power. In short, the coaxial section of line is “flat”.
It was still a lot of work to change bands but happily the VE4 Swap/Shop came to my rescue with a LDG Z11 auto-tuner. This needed a weather-proof box for outdoor use and ‘4XI came to my rescue with a boxed network intended for marine use…the contents provided some nice toroid forms, but the box was the main event! The LDG matcher is battery operated and has memories for quick QSY. I put a toroid on the output side to get a balanced feed out. Batteries, tuner and balun all fit the box.
Toroids. I stacked two cores together and made up a one:one winding. Primary side gets one lead grounded, secondary goes to the balanced feed. What I’m still trying to understand is how a toroid responds to a reactive load and it’s likely the load is reactive everywhere except some
sweet spot on 20 meters. The transmission line is a halfwave and so the antenna feed-point impedance is repeated at the matching network. But remember we only have a 20 meter antenna. Any other band is going to be a mismatch. Likely on any other band, the reactive current could go up and saturate the balun core…the current in a matched load (again 20 meters) at a kilowatt will be 4.4 amps and an AM peak of 8.8 amps. I’m running a hundred watts max, (1.4 amp peaks on SSB). How reactive can the system get before I saturate the toroid? I haven’t found a lot of information…but suppose I do run a kilowatt and plate modulate the transmitter, my peak currents will be significant for those toroids even if no reactance is present…
Another point to make is that the dimensions, lengths etc, are not critical except for 20 meter use (where they become important, not critical) without a matching network. If you have a network, you can deal with the construction errors. Note also that the 1/2 wavelength of transmission line is a 1/4 wavelength on 40 meters and you get a high impedance at one end of the line and low at the other end…I won’t tell you which, hi! You can do the math for the other bands. And another observation is that the antenna feed-point might be 75 ohms and the transmission line is 500 ohms dimensionally…next?
This G5RV antenna has worked very well for me. It is about a half-wave above ground on 20 meters and oriented along a north/south line. I’ve copied Great Britain, France, Holland, Belgium, Australia and New Zealand in the winter months here.
Notes: 1. A Multiband Antenna System for the Newcomer, Lewis G. McCoy QST March 1959. A Transmatch For Balanced and Unbalanced Lines, Lewis G. McCoy QST October 1966. My gratitude to Joe,’4XI and to Lee,’4ANC for his ability with a fishing pole to get pull lines up in the forest and suspend the wires.
After about a year, I had a line fail at the tie down point and the cut end went up into the trees. After a little thinking, I got out the extension ladder, up the tree and I could just catch the line with the poles from the roof-top snow rake. After supper (thinking time?), I went for the double-faced carpet tape and wrapped the end of the pole, reached up and twisted the rope to the pole/tape and got all back together and down to earth. I suspect I had a squirrel event…tasty rope.”
Thanks, Skip. VE4AY and I have been friends since we met in Winnipeg at the University of Manitoba Amateur Radio Society in the late 1960’s. Skip and I also share a background in broadcasting. He worked for many years maintaining transmitter sites with Sound Broadcasting Limited.