Jim, the original G5RV is a 1-1/2 wave 20 meter *only* antenna that offered a good match for the coaxial line by using an open-wire matching section. As you know, such matching sections are frequency-dependent, like any fixed tuned matching network. The G5RV allowed the use of the newly-available (at affordable prices) coaxial lines that appeared at the end of WWII.
Louis Varney (G5RV) contributed to the discussion of using his 20-meter "G5RV" on other bands. That's what causes a lot of confusion. At the time Varney published his original design, many Hams operated on only one band. That changed dramatically in the years after WWII, particularly in the 1950's. The rapid availability of surplus parts and entire rigs, a rather affluent post-war society here in the USA, and a large number of commercial and kit rigs appearing on the market in the 50's made multi-band operation "normal" for most Hams. Hams, always willing to "try anything" for an antenna -- even loading up the bedsprings (literally!), wanted to use Varney's G5RV design on more than 20 meters. Of course, the G5RV is nothing more than a doublet fed with open wire line, an efficient multi-band design that had been popular since the 1920's. Varney's contribution was the use of a specific open wire line section to match to coaxial line on 20 meters without the need for an antenna tuner (ATU). Ignoring the matching section and simply using it as a multi-band doublet worked fine, as long as one used a suitable matching network (ATU) and avoided the coax section. The problem was that Hams wanted to use coaxial lines. Not only were they easier to run into the shack, virtually all post-War rigs were designed for coaxial feedlines for simpler bandswitching and TVI-proofing. So the battle to find a suitable compromise between efficiency and the use of coax in a multi-band "G5RV" started in earnest. Varney himself wrote about those attempts, emphasizing the need for a matching network (ATU) on any but the 20 meter bands or if the dimensions of the antenna or feeders were changed in any way. One of those taking up this challenge was ZS6BKW who wrote a computer program to study and optimize the best combination of length and feeder for a G5RV-like antenna. His design provides a decent (<2:1 SWR) match on 7, 14, 18, 24 and 29 MHz but shows quite high SWRs on 3.5, 10, and 21 MHz.(see "Practical Wire Antennas" by John D Heys, G3BDQ, published by the RSGB, page 22). Ron AC7AC -----Original Message----- In all the G5RV articles I've read, including the original, it's a multiband antenna. It was specifically designed that way by G5RV. What's special about the G5RV is that if it is properly built and installed, it will present a low (but not 1:1) SWR and good efficiency on the non-WARC bands. And it's simple. > The same thing happened with the single-wire fed > Windom years ago. EVERYONE had them. > That antenna goes back to the 1920s. The "Windoms" we have today are really off-center-fed (OCF) dipoles. > Why would one want to clobber up an open-wire fed dipole? > The G5RV version requires a tuner when used on bands other > than 20M, so why not bring the open-wire to the tuner and > dispense with the open-wire-to-coax transition kludge hanging > outside in the sky? It's a simple application made difficult. No, it isn't. The reason for the popularity of G5RVs and OCFs is this: Properly made and installed, they are capable of low SWR (not unity) on multiple bands, and they wind up with a coax feeder of random length coming into the shack. While a tuner may be needed to get 1:1 SWR at the rig, the tuner need not be balanced, nor does it need to have a wide matching range. A simple, low cost tuner can do the job of tuning out the relatively-small mismatch. OTOH, if you simply put up the classic dipole-fed-with-ladder-line and don't concern yourself too much with lengths of dipole and feeder, the result can be a wide range of impedances at the shack end of the line. So you need a much more expensive tuner to get the system to work efficiently. All three systems will work well if done right. After all, they're all just dipoles with different feed systems. The question is, what resources are available? 73 de Jim, N2EY _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
