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Author Topic: CQ CQ G5RV users. ?? about height/directivity wi  (Read 614 times)
KC9BQA
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Posts: 7




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« on: August 14, 2002, 08:28:17 AM »

    I'm a new tech who has been a SWL/ham monitor for over 20 years.  I may very well want to get my general ticket over the winter.

    In the meantime, I have decided to put a G5RV wire antenna up in the tall trees that surround my place.  The G5RV the AES store near me sells is the 102' type for 80-10M, with the 30' tail of ladder line.

    The guy who's going to help me will get the antenna up about 40-45'.  From what I've read about G5RV's here at eham.net, it seems that their performance is improved when they're higher.  Since my primary listening interest is DX, I know higher would help.

    So this has got me thinking a little... I have a few questions.

    1)  Since the G5RV is a dipole, it has at least some directivity.  I understand that directivity is stronger the higher the antenna is installed.  What I'm wondering is this:  Is it worth it to install 2 G5RV's, perpendicular to each other?  I have enough trees to choose from that I could do this.  I could switch between the two antennas at the radio and (in theory) peak and null certain signals.  

    2)  At what height would the G5RV's need to be installed to "see" enough directivity to make installing two worthwhile?  It's possible that the antennas could be installed closer to 55-65', if I persuaded the tree guy nicely. Wink  Is the extra 10-20' of elevation going to make much of a difference?

    3)  If I did decide to hoist two at 90 degree angles to each other, how far apart would the G5RV's have to be (vertically and/or horizontally) to not interact negatively?  The antennas would criss-cross in the middle if they were at the same exact height.

    Asking question 3 just got me wondering... (always wondering, hi hi) is there any way to phase and/or array 2 G5RV's so that they would perform better than 1?  Would installing two in the same direction but at different heights help any?  Or hurt things?

    As you can see, I'm really trying to optimize things here.  I realize the G5RV is no beam.  I may be trying too hard here.  It wouldn't be the first time. Smiley

    Basically, I'm just trying to find out how to get a little bit of an extra edge from a simple antenna.  If what I'm trying to do isn't really going to give any extra performance, please say so.  I don't want to just have antennas up in the trees for no good reason.

    Thanks for your time and your responses.

    Todd
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WB2WIK
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Posts: 20613




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« Reply #1 on: August 14, 2002, 09:39:21 AM »

Any doublet's directional characteristics are highly dependant upon its length and operating frequency.  The G5RV is a shortened 80m doublet and has very a very broad pattern on that band, generally favoring its broad sides.  It's a 3/2 wave dipole on 20m, and has something like a clover leaf pattern (nearly omnidirectional) on that band.  It's an overly long dipole on 15m and above, and will tend to have directionality, favoring signals off its "tips" (or wire ends), and not the broadside, like a 1/2-wave dipole would.  

So, to set it up optimally, you'd have to choose "which band" you're setting it up for.  There's no single "right way" for a multiband doublet such as this.

You could criss-cross a pair of them at the same height and there would be virtually no interaction if the doublets were truly at 90 degrees to each other.  However, what you'd gain from this is questionable, and probably very little.

The G5RV needs an antenna tuner, usually for all bands except 20 meters.  Using a good, wide-range tuner will make it work far better than it could without one; so, I'd probably focus on this issue.  I wouldn't invest a lot of time or energy in a G5RV installation -- it's just not that great an antenna.*  When you achieve the General ticket, celebrate by putting up something better!  What a nice celebration that would be.  

*It's a resonant, 3/2-wave dipole on 20m.  On all other bands, it's quite a compromise.  I've always found that a resonant dipole for 80 or 40, or any other band (except 20m) outperforms a G5RV "hands down," no contest.  You might, in the future, consider parallel dipoles, or a big loop with a remote tuner, to really enjoy the property you have available.

73 & good luck!

Steve, WB2WIK/6
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AC5E
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« Reply #2 on: August 14, 2002, 10:40:48 AM »

HI Todd: Before you put that G5RV up - go to www.radioworks.com and see what the guy who makes them, along with several other antennas, has to say about them. The info you get will be the straight skinny, instead of the many Old Ham's tales bruited about.

73  Pete Allen  AC5E
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WB2WIK
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« Reply #3 on: August 14, 2002, 12:32:03 PM »

Pete, interestingly enough, Jim (RadioWorks) on his "G5RV" data sheet pretty much recommends against using one, and going with his Carolina Windom instead!

(I agree.)

73 de Steve, WB2WIK/6
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AC5E
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« Reply #4 on: August 14, 2002, 02:21:52 PM »

Hi Steve: Yes, the G5RV is a decent enough 20 Meter antenna that can be used on other bands. Just like the rubber duckie on an HT. But there are sure a lot of better antennas, many no more expensive, and some that take less room than the G5RV.

73  Pete AC5E
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WB2WIK
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« Reply #5 on: August 14, 2002, 03:05:05 PM »

People have a tendency to believe in whatever they have, especially if they've nothing to compare it to.

A guy only about ten miles from me was raving about his "Isotron" antenna and how well it worked on 75 meters.  I drove up to his house with my mobile rig, and Hustler RM75S resonator atop the MO-2 foldover mast, parked in his driveway, and offered to make a comparison.  Armed with a coax switch and 100' of RG8X, I went to his shack and wired up the Isotron as "1" and the Hustler whip on my car as "2" and did a blind study with half a dozen guys on the air, on 3830.

Antenna "2" was 6-7 "S" units stronger than "1," for everybody.  "2" was the whip on my car, in the driveway.

Which is why playing with a _lot_ of different antennas is always fun -- the more, the better.

WB2WIK/6

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W1EBI
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« Reply #6 on: August 15, 2002, 04:37:06 AM »

Steve, do you have any direct performance knowledge or experience re the Carolina Windom vs. the W9INN multiband dipoles? Per our earlier correspondence, I am evaluating all options to improving the "OK" performance of my G5RV. My only way to get up around 40ft and also pass the spousal acceptance factor would be to use trees. Susceptible to wind movement, but maximum stealth. I have worked a number of stations with Carolina Windoms, and in fact had bookmarked the Radio Works website, but it got lost as "KS" and I really didn't look into it. Lots of good stuff there!

George
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WB2WIK
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« Reply #7 on: August 15, 2002, 06:52:52 AM »

The Carolina Windoms do seem to work better than G5RVs, likely because they provide a closer impedance match across all the bands due to the off-center feedpoint.  Still, my experience with the C.W. antennas (I've used a few, but only temporarily like on Field Day) is that they do indeed require a tuner to take advantage of multiple bands.

40' high and tree-supported is not a bad deal.  I've used wire antennas far higher than this, tree supported, by using pulleys and counterweights so that when the trees sway, the horizontal wire simply bobs up and down but no additional strain is created.  

If you've got some 40' high trees and like "stealthy" antennas, you might consider a delta loop (tree supported) instead, as per the "One Stealthy Delta" article in QST a few months back.  Ingenious system.  Invisible antenna, likely to work very well because it's always "perfectly" matched by the SGC autotuner installed at its feedpoint.  Thus, any length coaxial feedline will have very little loss regardless of frequency -- and that's a very important factor.

Although I don't need any "stealth" where I am, I'm considering that same antenna, just for the heck of it.

73 & good luck!

Steve, WB2WIK/6



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NB6Z
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« Reply #8 on: August 15, 2002, 07:31:37 AM »

Todd, I can answer some of your questions from my own experience:
40 to 45 feet above ground will give your HF wire a reasonable take off angle for DX on 20 thru 10 meters; and the radiation patterns will be pretty much per the theory...
I presently have 2 horizontal all band wires in a criss cross 90 degree configuration with one wire mounted 5 feet below the other. Only one of these wires is resonant by length to the ham bands (the NB6Zep Jr. is 65 feet long) and the other is a NB6Zep (
http://home.teleport.com/~nb6z/nb6zep.htm ) and basically a 20 meter EDZep. I use them on all bands and have detected very little coupling between the two antennas. I have a tuner/SWR meter for each antenna lead and can A/B switch them to instantly bring in signals from other directions. This works amazingly well, especially on 20 meters where the lobes are sharp and broadside to both the antennas. You will need to model your G5RV on a PC (or find a published graphic) to show you were the lobes are for each of the bands. (If the lobes were at 45 degrees on both the wire, I guess it would make no differrence wich 90 degree wire you use.) In your case with the 102 foot long wire, you will have multiple lobes on all the DX bands, and so the A/B switch will be less useful in general.
I suggest you would have more fun with 2 20 meter EDZep wires and then put up a seperate antenna if you want 80 meters also. Have fun...
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AC5E
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« Reply #9 on: August 15, 2002, 09:43:28 AM »

FWIW - I notice the ARRL Handbook has the SWR/transmission line loss figures on a 100 foot flattop on the various bands, from 160 to 10.

100 feet is only two feet off a G5RV's dimensions and the difference is trivial. It's worth a good hard look for anyone who is contemplating putting up a G5RV or a similar antenna.

73  Pete Allen  AC5E

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KC9BQA
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« Reply #10 on: August 17, 2002, 08:28:28 AM »

   I want to thank the elmers who kindly replied to my G5RV question.  I now understand that there are definitely better receiving longwires than the G5RV.  I did spend quite a bit of time at the www.radioworks.com site.  As such, I am now intrigued by the Carolina Windoms.  

   Again, thanks for the replies.  It means a lot to a new member here at eham.net.  I am going to start a new topic regarding Carolina Windoms.

   73,
   Todd
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W0OPW
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« Reply #11 on: August 22, 2002, 09:10:04 AM »

Your comment:
"1) Since the G5RV is a dipole, it has at least some directivity. I understand that directivity is stronger the higher the antenna is installed."

 is incorrect.  Antennas do not get more directive as their height is increased.  The ground losses decrease which will increase the overall gain.

 As we say: Higher is Better.
 Pat W0OPW
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KF9VH
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Posts: 72




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« Reply #12 on: August 27, 2002, 11:08:10 AM »

I have a Van Gorden G5RV up about 35 feet on a push up pole and it works like a champ. Some hams claim that it is poor on 40 and 75 meters but if works great for me. I had a wire up for 75 meters for a while and the g5rv works all most as well. I have talked all over on 40 also. The only band I have a problem with is 15 meters.

This has been the best $60.00 I have spent on ham radio.
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