From: edh@sqa.dsg.ti.com (ed humphries (ASOC))
Subject: G5RV Look-alikes
Reply-To: ed.humphries@hub.dsg.ti.com
Organization: Texas Instruments, Austin, Tx.
Date: Mon, 17 Aug 92 17:15:14 GMT

	With all the questions concerning the "G5RV" type antennas, I
	thought it might be time for a repost of my review from early
	last year. I built and successfully ran the shortened version
	described below in the inverted-V configuration. Enjoy!
	
	Multiband Wire Antennas
	By Ed Humphries - N5RCK

	The March 1991 issue of CQ Amateur Radio contains yet another
	discussion of multiband wire antennas. In his column "Radio
	FUNdamentals", Bill Orr, W6SAI writes about the original W9CXX
	multibander with its' complex copper tubing matching section.
	He then goes on to discuss the popular G5RV developed by L.
	Varney, which is widely built and commercially available. Orr
	points out the deficiencies of the G5RV: when built in the 
	original design it delivers reasonable SWR on the 7, 14, and
	24 MHz bands, but into a 75 ohm coax feedline that is awkward
	to load up on modern transceivers; when built with 50 ohm coax
	the SWR is poor on all bands, but it performs reasonably well
	when used with a "transmatch" antenna tuner. 

	The column skips over an intermediate antenna design discussed
	in the March 1986 issue of Ham Radio. Bill's column back then
	pointed out that W5ANB first proved you could successfully
	modify the G5RV, load it with 50 ohm coax and run without any
	antenna tuner. But the best design (so far HI) he discusses in
	both articles is the one by ZS6BKV. Brian Austin used computer
	modeling to help him design a 5 band tuner-less antenna. Orr's
	CQ column reprints the design using only the dimensions for a
	300 ohm matching section (I presume TV flat lead qualifies). 
	In his original column Orr also presented the figures for using
	400 (handmade open-wire leads) or 450 ohm (ladder-line) as the
	matching section. Since 450 ohm ladder-line is somewhat stronger
	than the commonly available 300 ohm TV lead-in, I'm here giving
	both sets of figures so you can make your own choice.
	
	<  90' 3" for 450 ohm matching section or 92' 2" for 300 ohm >
	o-----------------------------oo-----------------------------o
                                      ||
        The ZS6BKV Antenna            ||
                                      ||
                                      || 40' for 450 ohm
                                      || 
                                      || 36' 9" for 300 ohm
                                      ||
                                      ||

	At the end of the matching section Orr recommends a 1:1 balun;
	others would say that several loops of coax at the feedpoint
	will do as well to help keep rf off the feedline. The feedline
	to the transceiver is common 50 ohm coax; RG 58/U is fine for
	hf for most runs. This antenna should give low SWR on 7, 14,
	18, and 24 MHz bands. At 28 MHz the SWR is really only good
	from 28.5 to 29.0. Tests showed the best SWR curves when the
	antenna was erected at about 42 feet above ground. When run as
	an inverted-V (90 degree) the resonant frequency came down 80
	kHz for 14 MHz and 125 kHz for 24 and 28 MHz. The March '86
	article printed SWR curves, and the March '91 article printed
	field patterns for all 5 covered bands. 
--
Ed Humphries                Texas Instruments, Inc. 512-250-6894
N5RCK                       Internet ed.humphries@hub.dsg.ti.com