Thanks to the efforts of N7WS and G3VGR, I now have pdfs of the 1958, 1966 and 1984 G5RV articles. What an incredible online community - within a few hours of a request, fellow amateurs a continent and an ocean away supply me with the information.
In a message dated 5/19/07 2:34:37 PM Eastern Daylight Time, [EMAIL PROTECTED] writes: > > Varney simply reverted to using his design as a center fed doublet on any > band except 20 meters! Of course, a center-fed doublet (random length > horizontal wire, broken at the center for low-loss open-wire feedline) has > been an well-known, efficient antenna since the 1920's. Varney offered > nothing new in his G5RV design except on 20 meters where the length of the > horizontal wire coupled with the matching section (33 feet of open wire line > of specific size and spacing) produced a tolerably low SWR for common types > of feed lines in use in 1946. It needed a matching network between the > feedline and the matching section on other bands, and was not optimized for > 50 ohm coax even on 20 meters! I have to disagree with this somewhat. The intent of the G5RV design, IMHO, wasn't to make an optimized antenna for 50 ohm coax or 20 meters, but rather to make one that would be a reasonable compromise for the HF/MF ham bands of the time. >From the referenced article, Varney writes: > > > "Although the impedance match for 75-ohm twin lead or 80-ohm coaxial cable > at the base of the matching section is good at 14 MHz, and even the use of > 50 ohm coaxial cable results in only about a 1.8:1 SWR on this band, the use > of a suitable matching network is necessary on all other HF bands.." > > Note the terminology: "Matching section" is the length of open wire line of > specific length, wire size and spacing used to match the center of the > horizontal wire to a feed line at the lower end. "Matching network" is what > we call today an antenna tuner or ATU. > > The matching network (ATU) should be at the end of the matching section > (open work line), not at the rig. Putting the tuner at the rig adds > significant losses to the system depending upon the type and length of > feeder used between the rig and the "matching section". Also, note that the > original design was optimized for 80 ohm coax or 75 ohm twinlead, both of > which were fairly common right after WWII. > But the actual added losses of using a tuner at the rig may not be worth worrying about. It all depends on the situation. > Post WWII rigs with tunable "pi-network" outputs could handle quite a wide > range of feeder impedances efficiently without resorting to an external > "tuner". We weren't particularly concerned about an SWR of 2:1, 4:1 or more > even if we had the means to measure it. So a 1.8:1 SWR was quite good. Of > course, with today's fixed-tuned rigs that's crowding the point at which the > rig will roll back power or shut down altogether to protect the finals > unless a tuner is used at the output to reduce the SWR the rig "sees". > Yup. In fact, towards the end of the hollowstate era, the matching range of many tube rigs was quite restricted, so that SWR of more than 2 or 3 to 1 was too much for them. Even with all-open-line feed, G5RV developed something worthwhile. The classic dipole fed with ladder line and a tuner can be made to work on all bands even if random lengths of dipole and feedline are used. But the impedances at the shack-end of the line may be very high, very low, and/or very reactive if this is done. What G5RV did was to come up with a set of values that result in easier-to-match values of impedance at the shack end of the line. 73 de Jim, N2EY ************************************** See what's free at http://www.aol.com. _______________________________________________ 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
