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Author Topic: G5RV  (Read 3093 times)
N0FPE
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Posts: 356




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« on: April 21, 2011, 03:39:08 PM »

I have heard it said that the G5RV antenna works equally bad on all bands! Is this true? And if that is true why do a lot of folks think they are better than a pocket on a shirt? Is this all another urban legend? Just wonderin!

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WB2WIK
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« Reply #1 on: April 21, 2011, 05:53:24 PM »

It's a good design that works well on 80-40-20-12 meters.  It's not good on 30-17-15-10 meters because its mismatch is very high.

The weakest signals I ever hear on 17, 15 and 10 meters are from G5RV users.  But on the bands where it matches pretty well, it's fine.

It models only 1 dB down from a full sized dipole on 80m, and about 2 dB gain over a dipole on 20m.

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N7DM
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Posts: 671




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« Reply #2 on: April 21, 2011, 08:02:34 PM »

[Multiband],[Vertical]....'simple' antennas work equally poor in all directions. I heard it when I was a kid. The overwhelming truth is that an antenna IS a conductor with RF current flowing in it, period. I've even used salty, wet, cotton cord. How well it radiates, where is radiates, both depend upon where it is placed. That is, how high, over what kind of earth [or water], and how much current you can get to race around in the conductor. Most of us are stuck with a few of those factors, that we cannot choose. "Making the best of a bad situation".  Old G5RV is credited with inventing a multiband antenna for 80/40/20/10... the only HF bands of the Era, and harmonically related. Further it was fed with open, balanced line of such length that the feed end of the line had a pretty low impedance, to match the low impedance link output... also of the Era. Well placed... it did as well as any other 'antenna'. Today... with a bunch more bands, hybrid feeds of baluns and coax's... it hardly looks like a G5RV anyway, and my short stack of poker chips is on darned near any antenna like my Field Day dipole [70 feet overall, fed with 450 ohm twin-lead], working at least as well. Of course, it seem 'today' that guys like to buy even wire antennas, and Lord knows, a guy will defend to the death that which he is stuck with!

I'm in my very well worn fox-hole............ let the mortar fire begin....

dm
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K8AXW
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Posts: 3598




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« Reply #3 on: April 21, 2011, 09:47:39 PM »



IIIIINNNNNNNNN COOOOOOOMMMMMMIIIIINNNNNNNNGGGGGG!!!!!!!
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KI4SDY
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Posts: 1452




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« Reply #4 on: April 21, 2011, 10:18:45 PM »

That's strange. Mine works great on 10 meters! Of course, I installed it according to the instructions!  Wink
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G3RZP
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« Reply #5 on: April 22, 2011, 03:14:31 AM »

The original used 75 ohm cable from the end of the 34 feet of open wire line. This was because in those days, the commonly available coax  was for domestic TV, and was (still is in the UK) 75 ohms. Coax was desirable because the transmitter was the G5RV 'Elizabethan' design, built with all anti TVI precautions in there, and a pi network tank circuit. Originally with one 807, later it had 2 to get up to pretty well the full UK power limit of those days - 150 watts. It was certainly the case that a lot of the metalwork was done at the Marconi research centre at Great Baddow, just outside Chelmsford. It would have been done as what was known as a 'Home Office' job by someone for a couple of packs of cigarettes.......

One of Louis' great regrets was that he never copyrighted the design, so lots of people have made money from sellling 'G5RV antennas', but he never got a penny! Originally, he was looking for good 20m performance, and he did quite well with it on that band. I knew him reasonably well: he and his XYL, Nelida, stayed with me a few times.
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N7DM
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« Reply #6 on: April 22, 2011, 05:59:47 AM »

Thanks for the expansion of info, OM. You mention Pi's and coax; as I recall coax is an outcome of WW2...Pi's to work INTO the unbalanced line [also making for a much cheaper Final Tank Circuit acting as a good L/P filter, too]  As I remember, I had first seen his design stuff in a Pre-WW2 magazine ?  Maybe not correct.... I *did* use what I thought was it, on a push-pull pair of 807 'valves'... link coupled output. Nice; NO MATCHING! Swing the link in, dip the plate... work EU......... HI HI

VY 73
« Last Edit: April 22, 2011, 06:01:52 AM by N7DM » Logged
G3RZP
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« Reply #7 on: April 22, 2011, 11:43:13 AM »

Coax was around before WW2. The 1936 ARRL Antenna Book (where my copy is, I know not) tells you how you make it. Use 1/2 inch copper tube and 14AWG wire: thread isolantite beads on the wire, and crimp either side of the bead to stop it moving. Crimper made from cheap electricians pliers with a small 'V' groove filed in each of the wire cutting jaws. Join the lengths of copper tube with suitable plumbing fixtures, thread wire and beads through. Very low loss, though.

Bigger stuff made much the same way was used on commercial HF point to point sites, too.

Louis published in the RSGB Bulletin in the 1950's and occasionally in the 70's and 80's in RSGB RadCom. The pi network was originally known as the 'Collins coupler', used by Art Collins pre WW2.
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N7DM
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« Reply #8 on: April 22, 2011, 12:35:53 PM »

Roger on the Home-Brew coax. I'm thinking of the 'usual' roll it out stuff. May be wrong there too, but...   I can't honestly say I ever saw anything about Pi Net's in output circuitry until maybe the '50's, when here in the States outfits like Harvey-Wells produced fairly cheap low powered gear.  I didn't have any, just homebrew and link coupled.  Fun times, they were.  Still happy to hear your input....

dm
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WB6BYU
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« Reply #9 on: April 22, 2011, 01:09:19 PM »

Quote from: G3RZP
...Coax was desirable because the transmitter was the G5RV 'Elizabethan' design...

I suspect that Louis didn't realize at the time what a range of advances in electronics (and everything
else) that era would encompass!


One of the reasons that the pi network (and later pi-L) became popular was that it was easily
bandswitched with reasonable parts, and provided some harmonic attenuation while matching
a wide range of impedances.  Previous circuits often required complex switching and/or plug-in
coils.

How well it works depends on many factors:  coax losses can be high on some bands, it could be
hard to match on 80m with the wrong coax length due to the low impedance at the feedpoint,
and it works best with a 1 : 1 current balun at the junction of the coax and twinlead (which G5RV
originally recommended against due to the poor performance of baluns of that era.)

I wouldn't say that the issues are the fault of the antenna, but more of the marketers who claim
it works all bands 10 - 80m (or 10 - 160m in some cases), and to some extent the users who
believe that if a tuner can match an antenna it must be working properly.

It's not a bad antenna to cover a few bands with a tuner.  VK1OD has a good analysis of the
expected efficiency on various bands using different feed methods here:

http://vk1od.net/antenna/G5RV/index.htm
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N7DM
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Posts: 671




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« Reply #10 on: April 22, 2011, 01:14:56 PM »

HI... Used to say a Pi was good for loading up nails and locomotives, but not much for Ham antennas... HI

I was just thinking that since the UK guys got to the Cavity Magnetron ahead of us, maybe you got practical, flexible coax sooner too. Rack my brain but I think the first coax I ever saw was in a WW2 Surplus Barn near Seattle in.... 1948? 

Oy................

dm
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WB2WIK
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Posts: 20540




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« Reply #11 on: April 22, 2011, 01:34:49 PM »

Coax was around before WW2. The 1936 ARRL Antenna Book (where my copy is, I know not) tells you how you make it. Use 1/2 inch copper tube and 14AWG wire: thread isolantite beads on the wire, and crimp either side of the bead to stop it moving. Crimper made from cheap electricians pliers with a small 'V' groove filed in each of the wire cutting jaws. Join the lengths of copper tube with suitable plumbing fixtures, thread wire and beads through. Very low loss, though.



Coaxial cable was patented in the U.S. by AT&T on December 8, 1931.

However it came into popular use when American Phenolic (now "Amphenol") developed a way to extrude plastic dielectrics in 1942, which led to economical mass production.  That's why before WW2, almost nobody ever really saw coax except for experimental purposes. 
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N7DM
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Posts: 671




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« Reply #12 on: April 22, 2011, 01:55:20 PM »

Good info... 'fits', tnx.  Frankly, I never got into it. Still only use a short chunk of '58 from the Corsair output to the input link on the matching net'.......... Gads, same sort of rig I used back then.

Great Hobby, ain't it. That's why I have The Gear 'there', and this fool contraption HERE.  No cross contamination...........

QRU I guess. Happy week-end, All..................
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N2EY
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« Reply #13 on: April 22, 2011, 03:45:49 PM »

I have heard it said that the G5RV antenna works equally bad on all bands! Is this true?

No.

And if that is true why do a lot of folks think they are better than a pocket on a shirt?

Because, in their experience, the G5RV worked well for them.

Remember that any antenna is better than no antenna. And when HF conditions are good, you can make QSOs with a really mediocre setup.

To truly understand the G5RV, you have to understand the times when it was designed, and the compromises.

Is this all another urban legend?

No. There are a lot of myths about the antenna, but the truth is pretty simple.

Some things to remember about the G5RV:

1) It was designed to cover 80, 40, 20, 15 and 10 meters with "low SWR" - meaning less than about 4 or 5 to 1 on those bands. As W5DXP (see his excellent website) and others have shown, that performance can be wishful thinking, particularly on 10 meters. In those days, 80 meters for G5RV (in Region 1) meant 3.5 to 3.8 MHz and 40 meters meant 7.0 to 7.1 MHz. More important, 30, 17 and 12 weren't ham bands, so the design could rightfully claim to be an "all-HF-ham-band" antenna.

2) The G5RV was designed when most ham transmitters had tube finals and pi-network output circuits that would load into a wide range of impedances without a transmatch, and into almost anything with one. "Loading" meant "the final amplifier plate current dips to the correct value and doesn't burn up". Many hams didn't have SWR meters; what mattered to them was whether the antenna loaded and made QSOs.

3) The G5RV is a compromise antenna that would fit the typical English townhouse garden (what we Yanks would call "back yard"). Long feeder runs were pretty much impossible with such a setup, and an SWR of 4 or 5 to 1 through 50 feet or so of coax or twin-lead on 80 or 40 wasn't considered a problem. There was no easy way to measure or model the overall feed system efficiency back then anyway.

4) The original design used open-wire feeder (not twin lead, not window line) for the matching section and 75 ohm coax or 72 ohm Twin-Lead (yes, there was such a thing). 50 ohm coax and the window line now in vogue change the game. The length of the coax from the transition point to the shack can have a major effect on "matchability". So can things like height, how straight the antenna is, balun characteristics, etc.

5) Some years back, W3RV and I were able to get a home-made G5RV to have low SWR on 80, 40 and 20 CW, and acceptable SWR on 15 and 10 meters. But it took a lot of pruning and fiddling. Worked well - about the same as a half-wave-long coax-fed dipole. The advantage was the multiband capability. I prefer a W3DZZ-style trapped dipole nowadays.

6) Some time back I went on a search for the actual, original G5RV article(s). Not articles based on the originals or interpretations but the actual articles themselves. What I found was that G5RV hisself wrote articles in the RSGB Bulletin for July 1958 and November 1966, explaining the antenna. He later did an update in Radio Communication for July, 1984. The articles are out there on the web, free for the download. G5RV's explanations are graphical rather than numerical, and in some cases modern modeling software will show things more accurately.

7) In all of the original articles, the antenna uses a 102 foot dipole wire and 34 feet of open-wire line, then "any length" of 72-75 ohm Twin-Lead or coax to the rig. The possibility is also mentioned of using the ladder line all the way to the rig. If that is done, the recommended length of line is some multiple of a quarter wave at 20 meters, and a link-coupled balanced tuner.

8) There have been many variations of the dimensions, by authors other than G5RV himself. Most of these were attempts to adjust the minimum-SWR points, to use parallel line with a lower velocity factor, or both. One variant well worth considering is the ZS6BKW, which sacrifices 80/75 but has some advantages on the other bands.

9) The G5RV isn't magic. It's really just a feed system for a dipole about 100 feet long that permits the impedance at the end of the matching section to be somewhere in the vicinity of 50-75 ohms on several HF ham bands. It may have some slight gain (1-2 db) in some directions on some bands in some cases, but it's not a "DX antenna" any more than any other dipole.

10) Where 'modern' hams have trouble is that they put up a G5RV clone and then expect 1:1 SWR on every part of every band. It just doesn't work that way.

73 de Jim, N2EY

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W0BTU
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« Reply #14 on: April 22, 2011, 10:38:48 PM »

The G5RV works very well, on SOME bands. But there's a better design. See http://www.w0btu.com/g5rv_antenna.html and follow the links.
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