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1-10 of 14 messages
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Why are ham's using a G5RV??
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by ON4MGY on August 6, 2004
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Hello everyone,
I've experimented for a short time with a G5RV antenna and then switched to a doublet (with a real balanced tuner, not an unbalanced tuner with a 4:1 balun)
The doublet really outperformed the G5RV.
So my question, why are people still using a G5RV as a multi-band antenna?? You should now the G5RV was developed as a 20m antenna with some gain.
73
ON4MGY Nic
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RE: Why are ham's using a G5RV??
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by AC5E on August 6, 2004
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Nic, that's a good question. If we were talking about a simple wire 20 Meter antenna I would recommend Louis Varney's design without hesitation. Unfortunately, real world performance leaves a whole lot to be desired, particularly on 75 Meters and below.
The measured field strength with the antenna hung as a flat top at 65 feet, much above a typical ham's available supports, is far below what computer modelling predicts. At a distance of 75 miles, just over 100 km, there's some 9 dB difference between a G5RV and an 85 foot long trap dipole at the same height and mounted end to end with the 'RV.
In direct A/B testing almost any reasonably long doublet outperforms the G5RV on both transmit and receive below 4 mHz. Even a 105 foot doublet fed with a 9:1 balun that got hot enough to convince me there was a lot of loss there.
While I do have further investigation of the original design on my calendar, there are a number of G5RV variants that do a somewhat better job than the original on the lower bands. I would suggest one of those to anyone who insists on a "G5RV" type antenna.
73 Pete Allen AC5E
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RE: Why are ham's using a G5RV??
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by W7DJM on August 6, 2004
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I have NEVER used a G5RV, and if I have anything to say, never will.
What MY question is, is, is, HOW did we ever get to the point where we are calling things "G5RV Junior" "G5RV Senior", and "Double size G5RV"
By the way, there is no such thing(s)
G5RV is probably turning over in his grave.
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RE: Why are ham's using a G5RV??
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by K5ENA on August 6, 2004
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I have run tests with my 75 meter group between a 75 meter inverted vee and a G5RV, side by side. The fellows in my group report there's not a nickel's worth of difference between the two antennas in signal strength, if any at all.
73, K5ENA
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RE: Why are ham's using a G5RV??
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by W5DXP on August 6, 2004
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When the G5RV was invented, there were no WARC bands, and 12m is the only WARC band where the G5RV models out to be an effective antenna. Of the remaining bands, it does not work well on 15m and 10m. At best, the G5RV is a four band antenna. The series-section transformer causes a resonant point around 3.6 MHz on 80m. In the SSB portion of 75m, the G5RV carries a relatively high SWR on the coax so low-loss coax should be used. In addition, a 1:1 choke/balun should always be used between the coax and the balanced feedline. (The 9 dB of loss reported could be from feedline radiation.)
A well-designed G5RV is a pretty good antenna on 80m(CW), 40m, 20m, and 12m. I use one on all HF bands, but I vary the length of the series-section transformer to achieve a low SWR on the coax on all HF bands. 73, Cecil, W5DXP
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RE: Why are ham's using a G5RV??
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by N6AJR on August 6, 2004
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Origanlly designed as a 20 m antenna which will work on oher bands it is a great model for sales due to a catchy name and lots of promotion. Try a Fan Dipole and see what a real antenna can do!!
http://www.hamuniverse.com/multidipole.html
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RE: Why are ham's using a G5RV??
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by W8JI on August 6, 2004
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Mr. Nic,
The G5RV is NOT as bad as general rumor claims, unless someone built it wrong or installed it wrong or doesn't know how to measure things.
I challenge ANYONE to prove the claims it is all that bad on 80,40 or 20.
Built according to original spec it has moderate SWR on the low end of 80, the high end of 40, and 20 meters. On those bands it is less than ~1dB different from a "resonant" dipole fed with coax of the same length.
I blind A-B tested a G5RV against a dipole on 75 meters, and when I would say the dipole was a G5RV and the G5RV was a dipole, people would STILL say the G5RV was weaker (even though it was a dipole).
It's easy to look at this with numbers.
For example, a G5RV on 3.750MHz has 7.7dBi peak gain with an impedance of 35.7 -j297
The 450ohm ~30ft feedline has .473dB loss with that termination, and the input impedance is 28.5 j74.5
The loss in 20 feet of RG-8X would be .07dB into that termination, so the SYSTEM would have 7.7dBi minus .473dB minus .07dB for a total gain of 7.157dBi
A RESONANT DIPOLE at the same height has 7.98dBi peak gain and an impedance of 65j0. The loss in 50 feet (same total feedline length) is .267dB. Since peak gain is 7.98dBi minus .267 is 7.71dBi.
The difference between the G5RV and the dipole is 7.71dBi minus 7.157 dBi = .553dB
A typical cheap tuner matching the impedance of the coax would have less than .2dB loss, and even if we double that we only have 1dB total difference.
This is almost exactly what I measured in actual tests, and since the math and tests agree I can only conclude people are measuring things wrong or making up stories.
So the challange is this.....show me where the alleged loss is. I think it is in people's heads. Prove me wrong with facts, not stories. To show you how imbedded prejudice is, people now are raving about the Cebik dipole that has significantly more loss than the G5RV!! It's all in the name I guess.
73 Tom
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RE: Why are ham's using a G5RV??
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by W8JI on August 6, 2004
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by K5ENA on August 6, 2004 Mail this to a friend!
I have run tests with my 75 meter group between a 75 meter inverted vee and a G5RV, side by side. The fellows in my group report there's not a nickel's worth of difference between the two antennas in signal strength, if any at all.
73, K5ENA>>>
K5ENA,
That is EXACTLY what my tests showed, and it is also what the models show.
One of the loudest stations I work on 80 from Europe has a G5RV, and I used to regularly smoke people in pileups using one on 40 and 80 meters!!
My conclusion is some people don't know how to build, test, or install an antenna and so they hang this nasty but false idea out that the G5RV has high loss. This started the false rumors, and now they are impossible to stop with fact.
73 Tom
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RE: Why are ham's using a G5RV??
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by WB2WIK on August 6, 2004
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"Why are hams using a G5RV?"
Maybe, "because they can?"
Before Varney published his article(s), hams used all sorts of doublets of various lengths, fed various ways, and called them doublets.
I have a QSL card from G5RV which has a photo (not a great one) of his station and antenna. His antenna was a 204' long center-fed doublet, fed all the way with ladder line. Where was the "G5RV?" I thought that was kinda funny.
Also, some of the stories about G5RVs are curious, like the ones where hams claim to have been using them for 40-50 years. Maybe so, but Varney didn't publish his article until the mid-70s, so anything similar made prior to that wouldn't have been a "G5RV."
I think here's what happened: Somebody saw a marketing opportunity. "Hey, here's a doublet we can manufacture for about ten bucks, put it together in a plastic bag with an instruction sheet, and sell it for $40!" So, they did, and then many others did, too.
The "bad rap" for G5RVs may well be in poor deployment, as Tom says. I never spent enough time fooling around with one to care, but it is true that "on the bands" I often hear or work guys saying they have a "G5RV in the attic" (uh-oh) or a "G5RV up 20 feet as an inverted vee" (which wouldn't work well no matter what it was), stuff like that. I can't recall ever hearing anybody with a G5RV up 150 feet above ground who didn't have a good signal. But then, any sort of doublet 150 feet above ground would probably generate a good signal.
WB2WIK/6
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RE: Why are ham's using a G5RV??
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by X-WB1AUW on August 6, 2004
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My theory is that many new hams are buying it because it is a “multi-band” antenna that is less expensive than other multi-band antennas.
As new hams, they lack experience and theory on how antennas work, and more specifically, under what circumstances, an antenna’s performance decrease dramatically.
I also believe that since new hams start on VHF/UHF, they buy antennas for mobile and “base” use. When they start getting on HF, they are used to buying antennas instead of making simple wire “dipole” antennas.
One of my first antennas was a trap dipole for 40 and 80 that I mounted on the TV mast on the two story house I lived in; that was the only way I could get all that wire up in the air, as an inverted Vee over the house. Worked great for me as a Novice. Could have saved the cost of the 40 meter traps if the internet was around so that I could have read about more than one “dipole” strung out from the center of the 80 meter inverted Vee.
I didn’t have the internet to ask questions about the problems I created with it.
One problem I created was following the Yaseu owner’s manual when it said to run a ground wire. I was on the second story and ran a small diameter ground wire from the rig, out the window to a rusty old ground rod that had been used years ago to ground a TV antenna mast.
73
Bob
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