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Author Topic: resonant antennas and open wire line  (Read 12321 times)
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w5hro
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« Reply #25 on: December 27, 2009, 12:20:06 PM »

Since certain touchy feely types like to base their claims on hearsay or antenna computer simulators check out the G5RV simulator screenshot attached below.

Notice the matching section's vertical polarization on both 40 and 80 meters?

 Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin


* G5RV.jpg (395.88 KB, 1796x1070 - viewed 183 times.)
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W2VW
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« Reply #26 on: December 27, 2009, 12:51:10 PM »

Since certain touchy feely types like to base their claims on hearsay or antenna computer simulators check out the G5RV simulator screenshot attached below.

Notice the matching section's vertical polarization on both 40 and 80 meters?

 Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin


Er uh. Sorry I don't do any modeling myself just lots of real antennas. When I want something modeled I ask da boys to do it for me.

Am I reading your screenshot correctly or are you stating that -73 dBi represents vertical polarization?
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w5hro
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« Reply #27 on: December 27, 2009, 01:22:59 PM »

Er uh. Sorry I don't do any modeling myself just lots of real antennas. When I want something modeled I ask da boys to do it for me.

Just go to some of the British websites. There's a billion websites on the G5RV and each one says something different. That screenshot was just one page from a complete G5RV evaluation from the radio organization over in England.

I read another article yesterday that said the matching section must be exact and its bottom must be at least 1m above ground for the lowest frequency of operation otherwise the antenna will radiate vertically on those lowest two bands.

With all of the ready-made G5RVís available today there is no telling if they are all made correctly or not. Did they use 450-ohm window line or 390-ohm line? Were the right calculations made, etc., etc., etc. If you built it yourself, what calculations did you use? Itís actually kind of scary.

A properly designed G5RV installed at the right height above REAL ground will probably work correctly. That probably rules out a few of the ready-made store-bought kind.
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k4kyv
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Don
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« Reply #28 on: December 27, 2009, 03:26:27 PM »


Just go to some of the British websites. There's a billion websites on the G5RV and each one says something different. That screenshot was just one page from a complete G5RV evaluation from the radio organization over in England.

I read another article yesterday that said the matching section must be exact and its bottom must be at least 1m above ground for the lowest frequency of operation otherwise the antenna will radiate vertically on those lowest two bands.

With all of the ready-made G5RVís available today there is no telling if they are all made correctly or not. Did they use 450-ohm window line or 390-ohm line? Were the right calculations made, etc., etc., etc. If you built it yourself, what calculations did you use? Itís actually kind of scary.

It's beginning to sound a  lot like audiophoolery.
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Don, K4KYV                                       AMI#5
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« Reply #29 on: December 27, 2009, 03:49:13 PM »

Er uh. Sorry I don't do any modeling myself just lots of real antennas. When I want something modeled I ask da boys to do it for me.

Just go to some of the British websites. There's a billion websites on the G5RV and each one says something different. That screenshot was just one page from a complete G5RV evaluation from the radio organization over in England.

I read another article yesterday that said the matching section must be exact and its bottom must be at least 1m above ground for the lowest frequency of operation otherwise the antenna will radiate vertically on those lowest two bands.

With all of the ready-made G5RVís available today there is no telling if they are all made correctly or not. Did they use 450-ohm window line or 390-ohm line? Were the right calculations made, etc., etc., etc. If you built it yourself, what calculations did you use? Itís actually kind of scary.

A properly designed G5RV installed at the right height above REAL ground will probably work correctly. That probably rules out a few of the ready-made store-bought kind.

So would you care to answer my question?

I don't need to do calculations to look for feedline radiation which only exists in your mind.
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N2DTS
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« Reply #30 on: December 27, 2009, 10:42:22 PM »

I used to run a home made g5rv, compaired to a resonant dipole fed with coax, it was a poor and noisy performer on 80.
If the open wire line was not the right length, the tuner had a hard time tuning it at a high voltage point on 80 meters.
My coax run was short, using RG214, about 25 feet of it.

Brett
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w5hro
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« Reply #31 on: December 28, 2009, 12:34:46 AM »

I used to run a home made g5rv, compaired to a resonant dipole fed with coax, it was a poor and noisy performer on 80.
If the open wire line was not the right length, the tuner had a hard time tuning it at a high voltage point on 80 meters.
My coax run was short, using RG214, about 25 feet of it.

Back in the mid to late 1980's when I was relicensed and started getting back on the lower HF bands I tried several different self resonate antennas. I didn't want to put additional posts up in the backyard at the time so I tried shortened antennas first. The G5RV was one of them. I also tried trap dipoles, but I kept shorting out the doorknob caps across the coils. They didnít like big continuous AM carriers for any length of time especially with modulation on top. I finally bit the bullet and put up a full-length 75-meter antenna with a 40-meter fan below it. RFI was an issue when operating on 40 meters though.

I later expanded the fan dipole to cover the other bands and the harmonic RFI radiation actually became worse than when I tried the G5RV. I really wiped out everything when on 20 meters. Everything was coax feed with 1:1 current baulns right at the antenna wires, but the tuning was always an issue in the shack and you had to be right on the antenna's resonate frequencies for each band to get a 1:1 match. I finally got smart and threw away the coax and went to the center-fed Zepp fed with window line and I have never looked back. Itís a better multi-band antenna scheme and it solved all of the problems I had with the previous antennas.

I think the G5RV is just really ďtouchy feelyĒ Grin as with most shortened antennas and everything has to be just right for it to work correctly. I personally would never try one again, itís not worth it, but if you have limited space it is a solution. Just be prepared for interference issues. When I searched around the net I found several different websites that had slightly different lengths when using 450-ohm window line. They were all within 1í to 3í of each other, but thatís probably just enough to make a difference using that particular antenna. The height above real ground is also important. It looks like the guy who started this topic has similar issues with his G5RV. He even gave his neighbors free Christmas light blinkers Wink
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KX5JT
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« Reply #32 on: December 28, 2009, 01:16:04 AM »

I suppose my experience with the G5RV is atypical.  Once I put a W2DU 1:1 Choke Balun where the coax transistions to 450 ohm windowline, all of my RFI and tuning issues dissappeared.  I can tune it 160 - 6 meters flat.   

Yet, I still wanna go with full sized doublet and a balanced tuner.  I just feel like it'll play better.
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Steve - WB3HUZ
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« Reply #33 on: December 28, 2009, 01:51:22 AM »

John, your situation is not atypical. I hear hundreds of G5RVs on the air and most have good signals. The ones who don't nearly always have them mounted at a very low height. In reality, they are indistinguishable from a dipole at the same height on all bands with the possible exception of 80 meters. Even on 80 meters, if low loss coax is used, the G5RV will only be slightly down. On the higher bands, they will have some gain compared to a dipole - after all Varney designed the antenna to produce a cloverleaf gain pattern on 20 meters, thus the 1.5 wavelength dimension for the flat-top portion.

There is nothing magic about them, either good or bad. That said, most people would probably be better served just running the ladder-line into their shack and matching it with a good tuner. Or they could just change the length of the feedline appropriately.

http://www.w5dxp.com/notuner.htm


For some non-audiophool type info on the G5RV, see the links below.

http://www.w8ji.com/g5rv_facts.htm
http://vk1od.net/antenna/G5RV/index.htm
http://vk1od.net/antenna/G5RV/optimising.htm
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Steve - WB3HUZ
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« Reply #34 on: December 28, 2009, 02:07:09 AM »

LOL. Someone appears to be clueless about modeling or what dBi means.


Since certain touchy feely types like to base their claims on hearsay or antenna computer simulators check out the G5RV simulator screenshot attached below.

Notice the matching section's vertical polarization on both 40 and 80 meters?

 Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin Grin


Er uh. Sorry I don't do any modeling myself just lots of real antennas. When I want something modeled I ask da boys to do it for me.

Am I reading your screenshot correctly or are you stating that -73 dBi represents vertical polarization?
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KX5JT
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John-O-Phonic


« Reply #35 on: December 28, 2009, 02:23:02 AM »

W8JI speaks some real truth about the G5RV!!  It really has a bad reputation that is often undeserved.  I've had on more than one occasion recieved a very nice signal report from somebody then I said my antenna was a G5RV and suddenly they recanted and my signal wasn't "as good as it should be", blah blah blah.....

Amazing.... if the G5RV is magical at all, it's that once someone hears that it's a G5RV it suddenly becomes 2 s units lower than it was!  It plays well on 40 and 20, very well.  I play on 80 meters with 50 to 100 watt carriers and seem to get great reports from other stations... especially if I never mention the antenna.  Grin

I heard someone the other day describe their antenna as a "102 foot doublet".   Heh, I chuckled knowing he had a G5RV and got tired of hearing the "detractors" put it down.



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Steve - WB3HUZ
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« Reply #36 on: December 28, 2009, 02:35:11 AM »

Yes indeed John. The G5RV has gotten a bad reputation. In some cases, it may be deserved. I've seen some versions that had the cheapest ladder line, a very small balun (probably lossy) and RG-58 as the coax. If you look at VK1ODs info, you can see the RG58 version shows the most loss - not really a big surprise.

Also, the G5RV is often the first antenna used by many new hams and it usually gets put up at rather low heights. Hey, a full-sized dipole will suck when it's only 10-20 feet off the ground and used on 80 meters.   Grin

You did the right thing by putting a good balun on yours.
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w5hro
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« Reply #37 on: December 28, 2009, 02:37:09 AM »

LOL. Someone appears to be clueless about modeling or what dBi means.

So what if it's -73 dBi down in the woodwork in that model? It doesnít erase the fact that if the matching section is wrong the antenna won't function properly. The one I got from Radio Works years ago was radiating like a M.F. Don't look at me, look at the place who made it. That was my experience with the G5RV and apparently I'm not the only one who has had the same type of issues. However, it wasnít as bad as the fan dipole. It was more of an RFI generator.

LOL, LOL and LOL !!!
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Steve - WB3HUZ
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« Reply #38 on: December 28, 2009, 03:19:41 AM »

-73 dBi is effectively zero. It's a purely mathematical number produced by the modeling software. It does not represent anything real. Math and physics are not the same thing. The fact that you don't understand this just destroys the validity of anything else you post on this subject. It may also explain why you had so many problems with the G5RV.  Cry
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KX5JT
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John-O-Phonic


« Reply #39 on: December 28, 2009, 03:47:53 AM »

Steve HUZ said:

Hey, a full-sized dipole will suck when it's only 10-20 feet off the ground and used on 80 meters.   

BUT I have worked a couple stations in FL (HOA hell) that used 80 meter dipoles at 12 feet and another at 18 feet just a few weeks ago and lo and behold!!!  20 db over 9 signals at the 100 watt carrier level!! 
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N2DTS
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« Reply #40 on: December 28, 2009, 09:19:13 AM »

That may be something they dont tell you about fan dipoles, while they might work very well on TX, they may pick up lots more noise, since they are resonant on all sorts of frequencies.

They do mention the harmonic radiation, but nothing about them picking up more noise.

I have the rump of the dxlb plus (160 to 10) as a 40 and up fan dipole, and noise on 40 seems much higher with it than the 40 only dipole.

I have had a lot of noise that sounds like a gasoline engine spark ignition noise, which is not there at all on the 80 meter dipole.
Its not a motor though...

I should just put up a 40 meter dipole in its place, and find something else for 20 and up.

My G5RV was up about 50 feet, and the TX seemed ok on all bands, but the rx picked up a lot of noise compaired to the resonant dipole.

Maybe that is the same effect as the fan dipole, its sort of resonant at various frequencies...

If you seperate the RX and TX performance, I think a number of antenna's work ok on getting rf into the air, but it seems like the rx performance varies widely between antenna types.

I noticed this dramatic difference when I had the dx-lb plus up (before it melted), it WAS resonant on 160, even though it was very short on 160, and I NEVER heard so many strong stapping signals on 160 before or since, tuning up other antenna's with a tuner did not come close at all.

Its quite an amazing difference between a resonant antenna and anything else I have tried, and if you extrapolate out the idea, it seems like a single band antenna that is resonant works best for RX.
It seems like it can be somewhat shortened, but if its resonant, it works well on RX.
As you add other bands, the noise goes up.

Brett

 

Brett
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KM1H
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« Reply #41 on: December 28, 2009, 10:38:33 AM »

When I moved back to NH from Chitown in 73 I put up a HB G5RV as the quickest way to get on the air while working on towers and better antennas.

It was roughly 60' high and strung between a pair of pine trees. The open wire feed was roughly 400 Ohms made from #14 and the balun was HB. Running around 600W I had no problem working DXCC on 80M CW over about 6 months, helped of course with a couple of Beverages as well as contests.

It also worked well on 40 & 20 but of course not on 15 where it isnt supposed to. And 10 was dead due to the sunspot cycle.

Quote
I used to run a home made g5rv, compaired to a resonant dipole fed with coax, it was a poor and noisy performer on 80.

That is a pretty good indicator of feedline radiation.

Carl
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« Reply #42 on: December 28, 2009, 10:39:14 AM »



So what if it's -73 dBi down in the woodwork in that model?


You posted that info in the first place to prove something about vertical radiation.

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W2VW
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« Reply #43 on: December 28, 2009, 10:42:37 AM »

out the idea, it seems like a single band antenna that is resonant works best for RX.
It seems like it can be somewhat shortened, but if its resonant, it works well on RX.
As you add other bands, the noise goes up.

Brett


According to this:

http://www.its.bldrdoc.gov/fs-1037/dir-031/_4576.htm

my 124' doublet is resonant somewhere in the 40 meter band.

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W2PHL
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« Reply #44 on: December 28, 2009, 10:53:58 AM »

That may be something they dont tell you about fan dipoles, while they might work very well on TX, they may pick up lots more noise, since they are resonant on all sorts of frequencies.

 Brett , I also noticed an increase in received noise when i added a second element to my 33ft veritcal. The second vertical element (connected at the feedpoint like a fan dipole) gives me 20m but the tradeoff seems to be more RX noise. Thanks for posting your findings.

Phil  
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« Reply #45 on: December 28, 2009, 12:01:28 PM »

Some day I'm gonna stretch a well-made G5RV between two towers at 130' high - and work the west coast on 75M AM using 10w - just to prove a point... Grin

T
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December / 1964    to    December/ 2014 will mark 50 years in this hobby.   Yikes!  Brrrrrrr.

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w5hro
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« Reply #46 on: December 28, 2009, 12:09:05 PM »

-73 dBi is effectively zero. It's a purely mathematical number produced by the modeling software. It does not represent anything real. Math and physics are not the same thing. The fact that you don't understand this just destroys the validity of anything else you post on this subject. It may also explain why you had so many problems with the G5RV.  Cry

BS, BS, BS, BS and more BS !!!

That model was just one model at a certain meter for a correctly matched feeder and what it shows is that vertical antenna polarization on the lowest two bands is in fact possible.

The other guy was right you "touchy feely types" just cant stand it when someone else gets on here and shares experiences that don't agree with yours. Its one of the main problems with the AM Forum.












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KF1Z
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« Reply #47 on: December 28, 2009, 12:15:50 PM »


The G5RV is, was meant to be, designed as,  a 20 meter antenna, albeit 3/2 waves long.

What happens if you use a 20 meter dipole on 75 meters?
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w5hro
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« Reply #48 on: December 28, 2009, 12:20:32 PM »


The G5RV is, was meant to be, designed as,  a 20 meter antenna, albeit 3/2 waves long.

What happens if you use a 20 meter dipole on 75 meters?


If fed with 50-ohm coax you'll be pissing in the wind.
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K3ZS
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« Reply #49 on: December 28, 2009, 12:57:05 PM »

A 3/2 length antenna fed in the center with coax should be about the same as 1/2 lambda dipole.
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