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03-31-2004, 05:02 PM
Hi,

Even though still a technician licensee, I think my real interest lies in everything HF, especially antennas.

I have been reading this (http://www.qsl.net/aa3px/g5rv.htm), trying to understand the G5RV.
Since a half-wave length reasonant dipole is a pretty straightforeword principle and formula, I'm having a hard time grasping the principles of the G5RV and what makes it an 'efficient' antenna.

For example, if I am understanding this right, does a section of the feedline become a reasonant part of the antenna below the 14 mHz range, or wouldn't always be a reasonating part of the antenna system? If it is, this can not be good for RFI, can it?

Not to mention the shortened versions of the G5RV (and shortened dipoles too) which add to my confusion.

I feel like wire is the way to go at my location and I would like to understand everything that is out there about them. If there are any good books on this subject I would appreciate reccomendations.

73

R.J., KC8ZBV

WB2UAQ
03-31-2004, 05:38 PM
Hello
The twinlead 1/2 wave long transmission line (at 20mtrs) attached to the feed point does not become part of the antenna proper. #In other words it does not contribute to radiation of the RF. #G5RV used this open wire line as a way to bring down the approx 80 ohms at the feed point down closer to the ground where he directly connected a coaxial cable without a balun. #The half wave line repeats the 80 ohms at this connection so the match is pretty good. #
There is however a windom ant that uses an imbalanced twinlead section to add a vertical component to the radiation of the ant system. #This might have been the source of confusion with the G5RV using its twinlead section to radiate as well.
I'm sure there will be more comments on this ant from others as there is so much out there. #If everything is cut in half, some of the advantages might be nullified. #We'll see from the other comments.

BTW, the First ARRL Antenna Compendium covers the antenna in an article by G5RV himself and Walt Maxwell covers it in his book "Reflections" also by the ARRL.

WA3KYY
03-31-2004, 05:47 PM
Try the following web site by L. W. Cebik, W4RNL. He has lots of good information on all types of wire antennas including the G5RV and it's variants.


W4RNL's Web Site (http://www.cebik.com/radio.html)

Look closely at the 88' doublet as a good, all purpose 80-10 M wire antenna. Also pay attention to his discussions of how patterns of wire antennas change with height.

Antennas are great to experiment with and you can get started while just listening to HF while preparing for your upgrade.

73,
Mike

K3STX
03-31-2004, 06:45 PM
ZBV,

I am most certainly NOT an antenna expert, but here goes. The G5RV is a good antenna for 20 meters. Period. It will work on other bands, but not as well as it "could". OK, so what is the problem, it is a "multiband" antenna. The problem with the G5RV, and the ONLY problem with the G5RV, is in that section of "coax" that is used to hook from the ladderline to your tuner/rig. Coax is TERRIBLE when there is an antenna system mismatch. You might be losing HALF of your signal into heat with some of the mis-matches between your 50 ohm rig and that antenna on certain bands.

So what to do? REMOVE THE COAX !!!!!! Unlike coax, Ladderline is very low loss, I don't have the numbers in front of me, but look in the ARRL Hanbook in the "Transmission Lines" chapter and they show the loss of a 100 foot dipole fed with either "low-loss" coax or ladder line. You will cry. If you remove the coax and feed ladderline all the way to your tuner you have a great all band antenna. Sure the SWR is high, but you can match the antenna/feedline system with your tuner and you lose very little. (Many people, including myself, have a 4:1 "remote" balun outside the shack so the ladderline hooks to the balun hooks to the coax hooks to the tuner hooks to the rig). It is great. I promise.

Just this morning had a QSO with a guy in Panama on 15 meters and my dipole beat my resonant vertical in an A/B test 599 to 599+10 dB.

Plenty of people love their G5RV and I do believe they work well for them. But I bet if they replaced that coax with more ladder line it would be even better.

OK, someone tell me I am wrong.

paul

BTW, there is a discussion of the "real" G5RV in Lew McCoy's book and if you SEARCH on G5RV on this site you will find more info than you can shake a stick at.

W5DXP
04-01-2004, 01:41 AM
The twinlead section of a G5RV is known as a series-section transformer. On all bands it transforms the antenna feedpoint impedance. Here is what EZNEC says about a 102' dipole fed with about 28 ft. of 300 ohm twinlead:

Freq antenna feedpoint transformed to 50 ohm SWR
3.8 36-j324 15.4-j8 3.3:1
7.2 583+j1200 28-j77 6.3:1
14.2 102-j44 114-j88 3.8:1
24.95 200+j338 80-j28 1.9:1

As you can see, the 50 ohm SWR is not terrible on any of these four bands. The other 4 HF bands don't fair as well as these.
--
73, Cecil, W5DXP

KA4GEH
04-01-2004, 05:17 AM
There is nothing magical about the G5RV. It is just a 102' flattop dipole (3/2 Wavelengths long at 20 meters). Alternately, you can think of it as a 1/2 wave dipole at 4.6Mhz, or so. Fed with ladder line, such a dipole can be expected to yield a reasonably useable match for many (but not all) frequencies over about a 5:1 frequency range, that is from about .5 X the design frequency to about 2.5 X the design frequency. In the case of the G5RV, then, from about 2.3Mhz to about 11.5 Mhz, or 80 through 30 Meters. The trick lies in the fact that length of the antenna was intentionally selected so that the frequencies at which it does NOT yield and acceptable matching range lie outside of a ham band. And that's all there is to it.

As the frequency of operation goes above the point where the antenna is more than 3/2 wavelengths long, the classical figure 8 dipole radiation pattern breaks up into many lobes, and it gets increasingly more directional off the ends of the antenna.

I have often wondered how useful a three-wire fan dipole would be with wires 204', 102', and 51' long, fed at the center with ladder line. Anybody tried this, or heard any performance reports on it? If used only in the Ham Bands, it would never be operating near the resonant length of any wire, so interaction between the elements should be a minimum.

04-01-2004, 04:49 PM
I love discussions like this. http://www.qrz.com/iB_html/non-cgi/emoticons/biggrin.gif

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote </td></tr><tr><td id="QUOTE">The trick lies in the fact that length of the antenna was intentionally selected so that the frequencies at which it does NOT yield and acceptable matching range lie outside of a ham band. And that&#39;s all there is to it.[/QUOTE]<span id='postcolor'>

Understood, thank you K4GEH.

Thanks to N6YMA also for the list of books, I will definitely be investing in these. I&#39;m going have to take some time out of my day and get the EZNEC program also&#33; I remember a friend of mine fooling around with it and it looked pretty interesting.

Thanks for everyone else&#39;s input on this, I really do appreciate it. Right now I think I&#39;m going to go rediscover the cebik website.

73,

R.J., KC8ZBV

KJ5XX
04-01-2004, 07:11 PM
I&#39;m going to have to disagree - the G5RV is NOT just a dipole with a 102&#39; flat-top. If it was, we&#39;d all be feeding it with coax since it&#39;s easier to handle and use.

For an excellent article on the theory behind the G5, this article explains in detail how the antenna behaves on all bands that it is designed for:

http://www.radiowavz.com/html/g5rv1.htm

I used a variation on the G5, a half-size version, fed all the way to the shack with ladder-line. I worked over 100 countries with this antenna and 100 watts. Even worked Siberia running less than 50 watts. If you&#39;re going to go with a wire antenna this is a great antenna. You might also consider looking at the Delta Loop......just a random length of wire (I use 157&#39; run in a loop from my 2nd story eaves, down and around my back fence and back up to the eaves).

Good Luck&#33;

w5rtx
04-01-2004, 10:28 PM
Of all the antennas I&#39;ve ever tried, the G5RV is the worst. Period.
Yes, you can load it with a tuner and use it mulit-band, but in my experience, it doesn&#39;t compare with a simple resonant dipole or a decent vertical.
73&#39;s

W5DXP
04-01-2004, 11:51 PM
To W5RTX, perhaps you aimed the lobes in the wrong directions.
73, Cecil, W5DXP

WA5KRP
04-02-2004, 12:30 AM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (w5rtx @ April 01 2004,16:28)</td></tr><tr><td id="QUOTE">Of all the antennas I&#39;ve ever tried, the G5RV is the worst.[/QUOTE]<span id='postcolor'>
Gary,


I wouldn&#39;t argue your point for a second. It simply goes to show identical antennas in different locations behave differently.

But the bell curve suggests that an enormous number of hams have found the G5RV serves them beautifully. Yes there are trade-offs. but as a multi-band antenna it has a lot to offer and a very long track record to prove it.

Aside from that, do you think the rockwall in Rockwall, TX. is a geological formation or some sort of ancient structure?


73


WA5KRP
San Antonio

W8JI
04-02-2004, 12:33 AM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (w5rtx @ April 01 2004,15:28)</td></tr><tr><td id="QUOTE">Of all the antennas I&#39;ve ever tried, the G5RV is the worst. Period.
Yes, you can load it with a tuner and use it mulit-band, but in my experience, it doesn&#39;t compare with a simple resonant dipole or a decent vertical.
73&#39;s[/QUOTE]<span id='postcolor'>
On occasion I see people say that, but it makes no sense. The SWR isn&#39;t that bad on 80.40 or 20 meters. If you calculate the losses of the entire system, it isn&#39;t much different than a dipole on those bands.

I had a few up here, and did some on the air tests compared to a dipole at the same height with both antennas in a clear area. When I would tell people it was a G5RV, they would almost always tell me the signal was worse. But when I would tell them the DIPOLE was a G5RV, they would still tell me the antenna I was calling a G5RV (even though it was the dipole) was worse.

No one can explain the reason for high losses on a G5RV (on 80,40, and even at times 20), I can&#39;t measure the losses, and I work a few DX stations with loud signals (compared to other DX in the same country) so my conclusion is the high loss is mostly &quot;invented&quot; or the product of a very poor installation.

If the G5RV was a person, there would be grounds for a federal discrimination lawsuit.

73 Tom

W5DXP
04-02-2004, 04:20 AM
Instead of emoting about the G5RV, would someone please publish some SWR and loss figures based on NEC (EZNEC)? I once set out to discredit the G5RV but I couldn&#39;t, at least not on 80m, 40m, 20m, and 12m. 73, Cecil, W5DXP

WA5KRP
04-02-2004, 07:01 AM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (w5dxp @ April 01 2004,22:20)</td></tr><tr><td id="QUOTE">Instead of emoting about the G5RV, would someone please publish some SWR and loss figures based on NEC (EZNEC)? I once set out to discredit the G5RV but I couldn&#39;t, at least not on 80m, 40m, 20m, and 12m. 73, Cecil, W5DXP[/QUOTE]<span id='postcolor'>
Emoting? http://mysmilies.ipbfree.com/s/contrib/edoom/_sure.gif


And you want someone to do your homework after you tried to discredit an inanimate object? #And FAILED?



Here. (http://www.qsl.net/k2hq/g5rv.htm)


WA5KRP http://www.computerpannen.com/cwm/cwm/3dlil/nonono2.gif
Anecdote

K3STX
04-02-2004, 11:29 AM
Nobody is trying to discredit the G5RV, only point out that, at least in theory, that section of coax has alot more loss in it than if it were replaced with ladder line. The same horizontal dipole portion with ladder line all the way to the shack would exhibit less loss on the various bands than would a &quot;real&quot; G5RV. Period. The difference might not amount to much in the real world, but if you care about dB loss the G5RV will have more. I think that is my only point.But if you DID use ladder line all the way it would NOT be a G5RV, in the same way there is no such think as a &quot;mini&quot; G5RV. If you change the G5RV it is not a G5RV anymore.

It is a perfectly good antenna, but changing it to a 102&#39; center fed zepp with ladder line would probably make it a much better antenna. I know there are published reports of the SWR on each band of the G5RV, all you have to do is imagine the loss of a 200:1 SWR on 50 feet of RG8.

paul

W8JI
04-02-2004, 02:31 PM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (K3STX @ April 02 2004,04:29)</td></tr><tr><td id="QUOTE">Nobody is trying to discredit the G5RV, only point out that, at least in theory, that section of coax has alot more loss in it than if it were replaced with ladder line. The same horizontal dipole portion with ladder line all the way to the shack would exhibit less loss on the various bands than would a &quot;real&quot; G5RV. Period. The difference might not amount to much in the real world, but if you care about dB loss the G5RV will have more. I think that is my only point.But if you DID use ladder line all the way it would NOT be a G5RV, in the same way there is no such think as a &quot;mini&quot; G5RV. If you change the G5RV it is not a G5RV anymore.

It is a perfectly good antenna, but changing it to a 102&#39; center fed zepp with ladder line would probably make it a much better antenna. I know there are published reports of the SWR on each band of the G5RV, all you have to do is imagine the loss of a 200:1 SWR on 50 feet of RG8.

paul[/QUOTE]<span id='postcolor'>
But what every misses is the SWR is NOT that bad on the coax, and even if loss is included and a SMALL cable like RG-8X is used the difference between the G5RV and a dipole on 80,40, and 20 meters is one dB or less.

It is only on the bands where feed impedance is through the ceiling that coax loss is high.

Some of the post about G5RV poor performance are clearly invented either through some installation error or measurement error (or I suppose the could just be fabricated reports).

There is absolutely nothing that supports claims that a G5RV is significantly worse than a dipole OR an antenna fed entirely with ladder line on 80,40, or 20 meters. As a matter of fact, the 88ft dipole LB Cebik suggests has significantly (a few dB) more loss than a G5RV on 80 meters. If his call was G5RV, the antenna would be a lynched by angry mobs and called a failure&#33; Since it is a W4 call, it escapes the mobs despite having more system loss than a G5RV.

I&#39;m constantly amazed at how crappy poor LF antennas like no radial verticals or Gap antennas escape the same mobs.

73 Tom

K3STX
04-02-2004, 06:03 PM
Was digging around to find SWR values for a &quot;real&quot; G5RV. I did not realize G5RV did not specify the length of coax needed to go the the tuner. Of course, there are variants, but modeling 102 feet dipole using 450 ohm ladderline for the transformer section:
75 ohm SWR at the base of the matching section:

80 meters 8:1
40 meters 4:1
30 meters 62:1
20 meters 2:1
17 meters 12:1
15 meters 23:1
12 meters 4:1
10 meters 33:1

Obviously fine on 80, 40, and 20, but 62:1 on 30 meters seems a bit high. Now with 10 feet of coax to your tuner you are obviously fine. Actually, as long as you can tune it with a tuner and get on the air on the band you want you are golden: people work the world with QRP all the time. It&#39;s a matter of efficiency.

Like I said before, I&#39;m not very knowlegeable about antennas and transmission lines, if Tom (W8JI) says something, I would certainly trust him.

paul

W5DXP
04-02-2004, 09:16 PM
http://www.qrz.com/iB_html/non-cgi/emoticons/wow.gif1--></span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (wa5krp @ April 02 2004,01http://www.qrz.com/iB_html/non-cgi/emoticons/wow.gif1)</td></tr><tr><td id="QUOTE">&gt; And you want someone to do your homework after you tried to discredit an inanimate object? And FAILED?[/QUOTE]<span id='postcolor'>
Nope, you missed the point. What I am asking for is scientific evidence that the G5RV is not a good antenna. I tried to prove that it is not a good antenna and failed. Anyone else trying to prove it&#39;s not a good antenna will run into the same thing that I did. The web page you provided simply proves my point.
--
73, Cecil, W5DXP

VK4XJB
04-02-2004, 10:03 PM
I know people that would be freaked out by the swr values given by both Cecil and Paul just on 80, 40 and 20.

Using the Cecil&#39;s figure of 6.3:1 for 40m because that is a for a 50 ohm coax and trying to compare with the coax I used for my 40m dipole. Hopefully I have this correct. I did a spread sheet using the formula in the arrl antenna hand book 17th edition.

When I had a dipole up for 40m it was fed with a length of rg58 with a measured loss of .69dB and length approx 60 feet. Slight mismatch with a #swr of 1.6:1. I calculate the coax loss to be .76dB.

By feeding the #28-j77 from the example giving a 50ohm 6.3:1 swr using the same piece of coax I calulate the loss to be 1.84dB. Just over 1dB higher. By using a better quality coax to reduce losses or use 75 ohm to reduce the mismatch, the line losses would be reduced.

Using the loss figures from the transmission line chapter. Using same length rg213 I estimate a total loss of .99dB with .64dB of that due to swr. Using same length rg59 a loss of 1.48dB with .88dB due to swr.

These losses are a bit worse than feeding a dipole but seems a reasonable trade off for multiband operation using coax feed. I would not call the losses signal killers.

WA5KRP
04-03-2004, 12:18 AM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (w5dxp @ April 02 2004,15:16)</td></tr><tr><td id="QUOTE">Nope, you missed the point. What I am asking for is scientific evidence that the G5RV is not a good antenna. --
73, Cecil, W5DXP[/QUOTE]<span id='postcolor'>
OOOOOOPS.


I apologize. http://mysmilies.ipbfree.com/s/contrib/legionxs/wavey.gif


WA5KRP
Texas

W5DXP
04-03-2004, 12:51 AM
http://www.qrz.com/iB_html/non-cgi/emoticons/wow.gif3--></span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (vk4xjb @ April 02 2004,16http://www.qrz.com/iB_html/non-cgi/emoticons/wow.gif3)</td></tr><tr><td id="QUOTE">&gt;These losses are a bit worse than feeding a dipole but seems a reasonable trade off for multiband operation using coax feed. I would not call the losses signal killers.[/QUOTE]<span id='postcolor'>
Exactly&#33; One dB of loss is probably not even noticeable except maybe for weak signal CW. The G5RV is not the most efficient antenna in the world but it is a good compromise to achieve 4 band operation on HF. And by adjusting the length of the series section transformer, one can optimize for one&#39;s band of choice. It is even possible to optimize for 30m at the expense of the other bands. The key is to allow the series section transformer to transform the antenna feedpoint impedance to a current maximum point. It already does that pretty well on 80m, 40m, 20m, and 12m with the standard measurements.
--
73, Cecil, W5DXP

K3STX
04-03-2004, 01:21 AM
I don&#39;t think the problem is when the SWR is 4:1, the problem is when it&#39;s 62:1 on 30 meters or 33:1 on 10 meters. I don&#39;t have a problem with the antenna either, but it is a good discussion so people out there can be motivated to read up on it. Perhaps we can agree it is a good dipole for 80, 40, 20, and 12 but not so good for 30, 15, and 10 meters. What a shock, there is no such thing as a free lunch.

By the way, can the &quot;average&quot; MFJ tuner match a G3RV on 30 meters?

paul

W5ALT
04-03-2004, 01:30 AM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (K3STX @ April 02 2004,21:21)</td></tr><tr><td id="QUOTE">By the way, can the &quot;average&quot; MFJ tuner match a G3RV on 30 meters?[/QUOTE]<span id='postcolor'>
Well, my &quot;average&quot; MFJ tuner can match a disconnected antenna on 30 meters. #http://www.qrz.com/iB_html/non-cgi/emoticons/tounge.gif

Yep, I&#39;ve done it, then finally figured out why the band seemed so dead ...

73,

W8JI
04-03-2004, 01:54 AM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (K3STX @ April 02 2004,18:21)</td></tr><tr><td id="QUOTE">I don&#39;t think the problem is when the SWR is 4:1, the problem is when it&#39;s 62:1 on 30 meters or 33:1 on 10 meters. I don&#39;t have a problem with the antenna either, but it is a good discussion so people out there can be motivated to read up on it. Perhaps we can agree it is a good dipole for 80, 40, 20, and 12 but not so good for 30, 15, and 10 meters. What a shock, there is no such thing as a free lunch.

By the way, can the &quot;average&quot; MFJ tuner match a G3RV on 30 meters?

paul[/QUOTE]<span id='postcolor'>
I don&#39;t think anyone ever said the G5RV was great on all bands, but I&#39;ve seen several say it stinks on all bands.

That just isn&#39;t factual.

By the way, the SWR figures and loss calculations are actually less if you use the G5RV on the low end of 80 and the high end of 40, or do a little bit of feedline and antenna length tweaking.

If eveyone whines so much about a half to one dB loss increase or tuner matching range, I wonder why they don&#39;t worry about the 2dB or 3dB feeder loss in using W4RNL&#39;s 88ft long dipole and the very poor impedance it presents to tuners? (The 80M SWR is something like 60 to 1).

Why don&#39;t we worry about Gap antennas or MFJ &quot;no ground&quot; verticals on 80 meters, where efficiency is about 10%? Or what about antennas like a B&amp;W dipole or the vertical from Germany that are loaded with a resistor and have 10dB or more loss on some bands?

73 Tom

AC0BE
04-03-2004, 02:04 AM
I really think this whole discussion would benefit by viewing the basic flatop dipole as the &quot;standard&quot; and the rest as variations created to accomodate installation situations.

The G5RV is a variation of the standard and like most OCF dipoles, done to solve particular installation choices.

The various forms of the &quot;standard&quot; tend to be compromise antennas and the lore of enhanced (magical) performance will usually elude close examination by modeling.

So if I may make a suggestion, if you are looking to put up an antenna, start with the old standby and go from there. Do a little homework and make whatever changes you need to: some will have a big effect, some will make little difference, all will probably be at least a little less than the &quot;standard&quot;.

73 Steve

KA4GEH
04-03-2004, 02:55 AM
In general, the best way (from an efficiency point of view) to feed any center fed dipole, wheather resonant or not, is with balanced ladder line, not with unbalanced coax of any kind. Only in the special case of a center fed resonant dipole can one expect to get a good effiicient match and excellent performance using coax alone, and then only when the coax comes away from the feed point at a right angle to the radiator for at least a quarter to half wavelength. Otherwise the antenna&#39;s radiation pattern is distorted because RF flows in the shield as it becomes part of the antenna system. A 1:1 (or other ratio) balun at the feed point will alleviate this problem. But again, only in the case of a center fed resonant dipole.

Once you move off the frequency of resonance for a given antenna, balanced open wire (ladder line) all the way from the antenna to the tuner or rig will nearly always outperform any unbalanced coax or mixed (coax / ladder line) feed system. That is not to say that ladder line will necessarily insure a great antenna with any length of wire in a dipole configuration, only that it will probably do a measurably better job than anything involving unbalanced coax and/or a balun in the same non-resonant configuration.

That said, there are reasons other than efficiency that usually govern the design of a given antenna application. A rotten radiator is always better than no radiator at all. It may not be optimal, but it will work. Back when the G5RV was invented, there was no 30 meters. Not surprisingly, 30 meter performance was not a big factor in the design. The idea was to find a particular length of wire that would exhibit its characteristic (and difficult to match) high impedance points outside of as many ham bands as possible. (It is a multi-band antenna, not an all-band antenna) It put the unmatchable points at frequencies no ham wanted to match to anyway. The idea was to get a single wire that would enable a practical tuner to match the wire on as many bands as possible. Not all bands, and maybe not even a great match, but at least something that one could work with. By this standard, I think history has judged G5RV&#39;s design a success. It is not a bad antenna, nor is it a great antenna, but it is a very practical antenna for a lot of hams. And yes, it is unquestionable that individual resonant antennas for each band will usually outperform a G5RV. But that might not be a practical possibility for many hams.

Another serious design criteria is that many of us don&#39;t have a operating position that lends itself well to using ladder line alone. We need to use coax to route our feedline through walls, attics, HVAC spaces, and other odd places. G5RVs design is a workable compromise for us.

Now, one could apply the same principle to the design of an antenna that would yield better performance on those bands that a G5RV doesn&#39;t match well. Compute a dipole length that yields practical impedance points for 30 and 10 meters, and/or any other bands desired. Chances are it will perform well there, but miserably on 80, 40 , and 20. Ya makes yer compromises and cuts yer wire accordingly.

BTW, one night many years ago, I worked Oslo, Norway??, in the 40 meter novice band, with a Heath DX40 running into a cantenna dummy load. I did not get a 59 report, but I did get a QSL card. I think most hams have had similar experiences.

W5DXP
04-03-2004, 03:52 AM
OK guys, here is as near perfect as you can get with a G5RV. Take a look at my web page to see how I vary the length of ladder-line using relays or knife switches. This perfected G5RV will work on all HF ham bands with a 50 ohm SWR of 3:1 or less, making it suitable for transceivers with internal tuners.

The key to perfecting the G5RV is to have a binary selection scheme that allows one to switch in one foot and/or two feet and/or four feet and/or eight of ladder-line. This allows a variable length of series section transformer from 20 feet to 35 feet. The basic series section length is 20 feet and then the rest is selectable from zero to 15 feet. I do this all the time to tune my dipole to a current maximum point.

Here are the different frequencies with the length of the series section transformer predicted by EZNEC and MicroSmith.

Freq: length of 300 ohm section
3.8: 29 feet
7.2: 33 feet
10.125: 20 feet
14.2: 31 feet
18.14: 35 feet
21.3: 28 feet
24.95: 29 feet
28.4: 22 feet
29.5: 21 feet

So there you have it. Roll your own G5RV optimized for the band of your choice. Please take a look at my web page to see how to vary the length of the ladder-line using relays or switches. I do it at the operating position using my 130 foot dipole but a G5RV could be modified at the twinlead/coax junction to accomplish the same thing. Obviously, the switching circuitry would need to be waterproof and physically accessible or remotely controlled. Maybe I&#39;ll do just that.
--
73, Cecil, W5DXP

W5DXP
04-03-2004, 03:55 AM
Sorry folks, my web page address is:

http://www.qsl.net/w5dxp/notuner.htm

W8JI
04-03-2004, 11:48 AM
http://www.qrz.com/iB_html/non-cgi/emoticons/wow.gif4--></span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (KC0OZU @ April 02 2004,19http://www.qrz.com/iB_html/non-cgi/emoticons/wow.gif4)</td></tr><tr><td id="QUOTE">I really think this whole discussion would benefit by viewing the basic flatop dipole as the &quot;standard&quot; and the rest as variations created to accomodate installation situations. #

The G5RV is a variation of the standard and like most OCF dipoles, done to solve particular installation choices.

The various forms of the &quot;standard&quot; tend to be compromise antennas and the lore of enhanced (magical) performance will usually elude close examination by modeling.

So if I may make a suggestion, if you are looking to put up an antenna, start with the old standby and go from there. #Do a little homework and make whatever changes you need to: some will have a big effect, some will make little difference, all will probably be at least a little less than the &quot;standard&quot;.

73 #Steve[/QUOTE]<span id='postcolor'>
Hi Steve,

The G5RV is not an OCF (off center fed) dipole.

It is a regular dipole with a matching stub.

73 Tom

W8JI
04-03-2004, 12:11 PM
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (ka4geh @ April 02 2004,19:55)</td></tr><tr><td id="QUOTE">[/QUOTE]<span id='postcolor'>
In general, the best way (from an efficiency point of view) to feed any center fed dipole, wheather resonant or not, is with balanced ladder line, not with unbalanced coax of any kind.&gt;&gt;&gt;

That isn&#39;t correct. Coaxial feed and other methods are very efficient.

Ladder line is OK, but it isn&#39;t as lossless as people seem to #think. The punched out twinlead called ladder line isn&#39;t much better than twinlead.

In all HF transmission lines of reasonable design, the dominant losses are conductor resistance losses.(The exception is wet twinlead like ladder line. It is pretty bad when wet.) Even dry ladder line 1/4 wl long with a thin conductor can have more loss than coax when feeding a 1/2 wl dipole.

#Only in the special case of a center fed resonant dipole can one expect to get a good effiicient match and excellent performance using coax alone, and then only when the coax comes away from the feed point at a right angle to the radiator for at least a quarter to half wavelength.&gt;&gt;&gt;&gt;

Ladder line is no better. It ALSO has to come away at right angles or it will radiate and the system will be unbalanced.

There are two sources of common mode.

One is an improper junction of balanced and unbalanced transitions, like feeding a dipole (or vertical with less than perfect ground) with a coaxial cable. This bad effect is independent of the type of feedline and the angle of the feedline.

The other is when a conductor or feedline of ANY type is not at right angles to the electric field.



Otherwise the antenna&#39;s radiation pattern is distorted because RF flows in the shield as it becomes part of the antenna system. #A 1:1 (or other ratio) balun at the feed point will alleviate this problem. #But again, only in the case of a center fed resonant dipole.&gt;&gt;&gt;


That isn&#39;t true. &quot;Unbalanced current&quot; or more correctly common mode currents will flow on ANY conductor or conductors that isn&#39;t at right angles to the antenna. That includes ANY feedline. Adding a balun at the feedpoint can make it worse or better, but most likely won&#39;t do much of anything to help a feedline parallel with the antenna.

The actual correct place to add a balun (or common mode choke) when the feeder of ANY type parallels an antenna is where the feeder leaves the area of the antenna. #
That is not to say that ladder line will necessarily insure a great antenna with any length of wire in a dipole configuration, only that it will probably do a measurably better job than anything involving unbalanced coax and/or a balun in the same non-resonant configuration.&gt;&gt;&gt;

The exact answer depends entirely on the feedline and antenna configuration. I can show you many combinations of ladder line and coax #that are more efficient than ladder line alone, and that is when the ladder line is dry and clean.

There are also cases where coax is more efficient.
for a lot of hams. #And yes, it is unquestionable that individual resonant antennas for each band will usually outperform a G5RV. #But that might not be a practical possibility for many hams.&gt;&gt;&gt;&gt;

Yes indeed. You can gain an extra half-dB to one dB on 80 meters with a resonant dipole, and similar amounts on 40 meters&#33; #

Of course you can lose that amount if you jam-pack 10 dipoles in one small yard. Everyone misses the point that too many wires are just as bad as not enough, and assumes the non-used wires have no effect.

BTW, one night many years ago, I worked Oslo, Norway??, in the 40 meter novice band, #with a Heath DX40 running into a cantenna dummy load. #I did not get a 59 report, but I did get a QSL card. #I think most hams have had similar experiences.&gt;&gt;&gt;

You need to have a serious look at your antenna switch, the DX 40 power line decoupling or coax connector grounding, or station wiring shield connections, because you can be positive it wasn&#39;t radiation from the cantenna he was hearing.

73 Tom

AC0BE
04-03-2004, 08:45 PM
My apologies-

as W8JI has pointed out, the G5RV is not an OCF dipole.

What I REALLY wanted to say was that the G5RV, like OCFs and other dipole variations, is a compromise from the &#39;standard&#39; and has limitations but no magical properties.

Tom- thank you for your comment.

Steve

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