The AM Forum

Here is one for the x perts here

The idea is to construct a resonant diaperpole for each band 80 40 20 possibly 160 and feed it with either 450 window line or home made 600 open wire.
I will bring the lines to the shack and switch it there.

Being the lazy sort of gen xer that i am I would like to match this in a way that i will take advantage of the fact that the antenna is resonant and not have to go through a tuner.  Is there a way to match the low imp diaperpole to the ladder line and then the ladder line in the shack to the rig with no moving parts.
Basically use it as if the antenna was a co ass fed resonant.

things i cant rap my head around.

1) what load is seen at the end of say 100 ft of 450 line with a 80m resonant dipole at the shack end
2) could a single broadband network be used in the shack for the same antennas on 20 40 80 160
3) would the losses in such a network defeat the purpose
4) would it be so much work design and planning that its not worth it.

the reason for this is the g5rv although it works great  the coax losses (100 ft) are steep and on some bands the feedline radiation (coax) is so high that the tvi is scarry
I know I know 130 ft flattop balance line and a link coupled tuner... but thats the easy way out.. I wanna try something new.

nevermind.. just answered it myself 

would need either a delta or gamma match at the antenna and then a 9:1 transfromer and a 1:1 balun  at the feed.  a gamma match would not be practical on a wire and the delta would skew the radiation patter quite a bit... Link coupled tuner seems to be the best solutuion.

anyway Ive gotta run been working on a new wheel thats gonna be better than the old one

That would be a job for Santa

Are you talking about 3  seperate dipoles, with 3 independant feeds?

If so, can't you just make each feedline an even multiple of a 1/2 wave, and trim.. ?

The xmitter end of the feedline would just "mirror" the impedance of the ant... right?


OR take the easy way out, and use a JJ supa tuna   ;D

There is NO reason to use open wire line on an antenna with little or no swr.

Its only when there is a lot of swr on the feedline that open wire line pays off.

Brett

Regardless of type of feed line, go with the electrical half wavelenght of the resonant frequency the dipole is cut for. The impedance at the transmitter end will be around 72 ohms same as the dipole feed. 

Make sure you take the velocity factor of the line into consideration. OW is fairly high, ~0.85 or so depending.   

There will still be a mismatch at the antenna/feed line junction, unless you are using 75 ohm line that naturally matches a dipole (well it'll be close enough).   

Normally there's no need to worry about the mismatch at the ant/feedline junction. But if you want you can use any type of well designed transformer for that purpose. (for single band antennas aircore balun types work well and tend not to saturate like ferrite based designs. Also not as heavy.)

yes three different ants.

are you saying trim the feedline for a match or the ant

cost Weight and power

the ant supports here arenet very strong.. I live in a row home with a 20x90 back yard.  + 10 ft to the peak of the roof.

the roof end is a par of crap shack tripods and 12 ft masts 18 ft apart.. total height 45 ft
the far end are 2 50 ft telescoping masts and a 45 ft a little closer in.

I was a little concerned with running qro am through rg8x mini.. flex radio and several henrys 2kx 3k 5k
ther is no center support for the dipole as i have to keep things as un obvious as possible
I recently bough out my competition and ended up with about 6 miles of strand and solid electrical wire to make ants and feed with

anyone know how much it would take to fry rg8x feeding a resonant ant 1.5 to 1 or less

the rg8xmini  would only be about 60 ft long to a central point  ( the shed ) where i have 3 runs of 1 inch hardline (friends in the cellphone industry gave me several 120-150 foot leftovers)

Then something must be wrong with that G5RV. There is no reason for feedline radiation, either the coax part or open wire line part.  Feedline radiation means excessive common mode currents on the feedline.  If the antenna is balanced as it should be, the feedline radiation should be negligible.  Tvi is most likely a result of poor harmonic suppression at  the transmitter.

Open wire line may be  run as a  flat, untuned line or as a resonant feedline with SWR. One reason to  run open wire at low SWR would be if you wanted  to maintain balanced feeders. Even at 1:1 SWR, the losses in open wire line are much less than those of coax.  Flat open wire feeders would be useful, for example, for a very long feedline.  I measured 8% power loss in a 140 ft.  run of RG-214 "low loss" coax on 160m, at near 1:1 SWR. I'm sure a flat section of open wire line  running at 1:1 SWR would show less loss than that.

Strange.  My G5RV put a little rf into the shack but I added a W2DU choke balun where the coax meets the ladderline and that was history.  Also, it now easily loads up on all bands 160 - 6 meter.   Of course I know it's silly to try anything phone on 160 due to it not being very efficient, it does load flat with the tuner.  30 meters also loads now where it wouldn't before the balun was installed.  Before the balun, different bands and frequencies would kick my usb keyboard and mouse right offline, but this doesn't happen anymore either. 

Nevertheless, I'm planning to build a k1jj style link coupled super tuner and play with more copper than just 102'.

Merry Christmas everyone!
KX5JT

errr um sorry for the miss speak.. actually what is happening is on 40 meters anywhere on the band with anything over 100w i flicker every cfl within 800 feet of me.. one night for fun i ran a long cord for my keyer to the front porch.. the wife and i sat outside and watched the lights up and down the street indoor and out door blink in time with my cq call.. funny as hell.

don the line loss was not actually measured by me but taken from cebik who did the work at the end of a piece of 100ft 213  was about 10 db feedline loss on 80.

just weighing the options right now to make everything as efficient as possible.

spectrum analizer shows everything is good and clean at the output of the amp

Trim the feedline, same as you need to for a G5RV.
(of course this sort of implies to calculate the electrical 1/2 wavelengths in even multiples, and cut it a little long, so you can trim it down)

This is where a MFJ 259 or Autek RF-1, or VA-1 come in super handy..


You can't really trim an antenna to 'match it'.
Once the ant is cut for the freq you want it, leave it alone, if you trim it, it is no longer resonant for the freq you want..


But, I'm not sure if having 3 or 4 seperate mono-band dipoles is going to gain you much over a single doublet, fed with open wire line, and a good link-coupled tuner to cover all the bands.

One good reason for seperate dipoles is band vs. direction.

I have run 700 watts carrier, about 3kw pep into the stuff for years without any problems...

Brett


[/quote]

cost Weight and power

the ant supports here arenet very strong.. I live in a row home with a 20x90 back yard.  + 10 ft to the peak of the roof.

the roof end is a par of crap shack tripods and 12 ft masts 18 ft apart.. total height 45 ft
the far end are 2 50 ft telescoping masts and a 45 ft a little closer in.

I was a little concerned with running qro am through rg8x mini.. flex radio and several henrys 2kx 3k 5k
ther is no center support for the dipole as i have to keep things as un obvious as possible
I recently bough out my competition and ended up with about 6 miles of strand and solid electrical wire to make ants and feed with

anyone know how much it would take to fry rg8x feeding a resonant ant 1.5 to 1 or less

the rg8xmini  would only be about 60 ft long to a central point  ( the shed ) where i have 3 runs of 1 inch hardline (friends in the cellphone industry gave me several 120-150 foot leftovers)
[/quote]

If you go with 'small' coaxial cable consider mil RG-142...double silver shield / teflon insulation / solid silver inner. Will take serious power and is about the same size as RG-58.

 

Have I missed something re the G5RV?  As far as I can tell it is basically a slightly shortened dipole fed at the midpoint with open wire tuned feeders, which are then fed directly by a piece of coax line at a specific point where the transmitter end of the OWL presents a reasonably good match directly to the coax without a tuning network. Therefore, there should be no unbalance nor any radiation from the open wire line.  If the coax is looking at a mostly resistive load somewhere near its surge impedance, there should be low SWR on the coax, and little or no common mode current. This is not unlike the common practice of using coax to feed a balanced half-wave dipole directly at its midpoint without a balun, which often results in a good SWR and minimal common mode current on the outer surface of the braid.

Some people have even told me that part of the feedline of a G5RV is supposed to radiate, much like a vertical antenna, to give low angle radiation good for DX.  I always took that to be nothing more than some kind of Hammy Hambone urban legend.

So, could someone explain what causes the open wire part of the feedline to radiate?

That way makes it sound worse than it really is since the actual loss is only .25dB/100' at 2 mHz. Or put into a visual mode it takes 5-6dB per S unit.

With RG-8 foam it is .2dB and with a good RG-11 CATV foam cable it is only .1dB. If those sort of losses bother you then you have too much time on your hands ;D

Since I only use the RG-11 CATV cable and 75 Ohm hardline I dont have to continually lose sleep over losses, even with 400' to the 160/80M inverted vees.

For a dipole, use quad shielded and flooded RG-11 foam. Its light weight and with a balun there will be no feedline radiation even with a fairly high VSWR. It will handle all the power you can muster up with those Henry's.




That was your first mistake ::)

Carl
KM1H

I've seen a station make a 15 minute AM  OB test xmission on 75M using matched RG8X using xx KW pep... ;D   (into a dummy load of course)  The coax didn't even get warm. Never wud have believed it.   Coax can take a lot of power at the low freqs if reasonably matched.

Over here I have several 600' runs of 75 ohm  aluminum hardline to the tower/ antennas. I don't worry about losses that add up to less than a db.

T

Derb, looking at that aerial arrangement. If you want to play on 160M then I would suggest something along the lines of a folded unipole. Phil K2PG has been running one for years and he does quite well in the postage stamp lot he has in NJ.

I witnessed 2500W of A.M. carried by RG8X and it got warm. This was a 50 ohm antenna system tuned for 3.880 at a station in the N.E.
Fred

You have it right Don. Anyone who claims the feeders are supposed to radiate doesn't know what they are talking about.

 


Be careful about pointing out the fact that those who don't know what they are talking about don't know what they are talking about.

It upsets touchy feely types.

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?

It's beginning to sound a  lot like audiophoolery.

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.

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

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.

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

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

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.  ;D

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.

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.   ;D

You did the right thing by putting a good balun on yours.

-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.  :'(

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!! 

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

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.


That is a pretty good indicator of feedline radiation.

Carl
KM1H

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

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.

 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  

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... ;D

T

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?

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

I worked a w4 on 144.2 with my J pole. This proves that its OK for 2m DX.


Just a little bit more gasoline for the campfire.... ..


klc

A half-wave dipole is around 70 ohms (center fed) only when it is a half-wavelength in height over virtual ground.   At most heights normally used on 80 and 40 meters, it would be closer to 50 ohms.   It really will only result in a 1.5:1 mismatch no matter what coax you use.     Check out any of the antenna handbooks.   They usually have a graph of characteristic impedance vs. height above RF ground.

oops, we have a split thread.. I'll post this on the new thread... (i guess  ::) )

Hi All,

I’ve been too ill for the past few weeks to participate in the AMforum, but son Bill, W2WM, told me about the new thread discussing the G5RV. Before I became too ill to participate I started a detailed review of the G5RV, including a mathematical analysis of the so-called ‘matching section’. I intend to finish the review and post it here. I mentioned the review to Bruce (UJR), and he said he’d be interested in seeing it.

So now, if I may, I’d like to present a downright dirty abstract that will introduce the review when it’s finished. To begin, the G5RV is a good antenna, except that the design is atrocious. It radiates like any 102’ dipole, in spite of the outrageous feedline arrangement that Varney called ‘special’. I’ll probably incur a lot of antipathy with some here on the Forum with some of the remarks, which I know won’t go over well with everyone, but I have a thick skin.

First, the 33’ matching section performs no effective matching to a coax. The mathematical analysis I made that will be included in the review proves it. As Varney used it on 20m it performs no useful function, because 33’ is a half-wave on 20m—a 1:1 impedance transformer. If he had connected the coax directly to the radiator instead of the 1/2wl open wire the result would have been exactly the same. On all the other bands the 33’ open-wire line presents horrible mismatches, with high SWR to either 50- or 75-ohm coax. If you want the open-wire portion to present an input impedance near the impedance of the coax, the length of the open-wire needs to be engineered separately for each band—one length will NOT provide a match on all bands. Consequently, it is not a good arrangement for all-band use, because the feedline has too many deficiencies. For a good more simple all-band antenna that will perform every bit as well as the G5RV is a dipole around 125’ or 130’ fed in the center with open-wire line all the way to the tuna. (Varney used 102’ for the radiator only because he wanted a four-lobe radiation pattern and a low terminal resistance at resonance.) The characteristic impedance of the open wire is unimportant. IMHO, the G5RV is vastly over-rated, because it’s not simple to build for what one gets as the result of hard work.

Second, feedline radiation. If no balun is used between the open wire and the coax, feedline radiation from the coax is guaranteed, big time. Contrary to some of the present thinking, if current on the open-wire portion is equal and opposite on each side, there will be NO significant radiation from the open-wire portion, regardless of the SWR appearing on it. (The reason is explained in detail in Chapter 20 of Reflections, available on my web page at www.w2du.com.)

Third, if coax is to be used, it should be used only on 20m because of the high SWR on all the other bands. On 20m the open-wire section is of no use--unwanted baggage.

I’ll post the final review as soon as I’m able to finish it.

Walt

Thank You Walt and hope you feel better. Maybe some people will let this stupid antenna configuration die as it should.

I look forward to your analysis Walt. My quick analysis of the G5RV on 80 meters shows only about 1 dB of loss (not counting the balun) when using 50 feet of RG8 foam type coax. Some additional loss will occur in the tuner, but with a good tuner this should be minimal. Due to the low Z involved, a less than "good" tuner may incur larger losses.

For a G5RV at 60 feet above ground with average conductivity.

f: 3.8 MHz

Feedpoint Z: 47 - j322

Z at the end of 33 feet of 450 Ohm ladder line: 36.91 + j98.69
The ladderline loss is 0.5 dB

Z at the end of 50 feet of RG-8 foam-type coax:  9.65 - j0.78
The coax loss is 0.27 dB.

now what happens on 40

Hello Steve,

Re your post 58 above, I'll review it carefully when I'm feeling better, and up to it. What caught my eye, however, is the 0.5 dB attenuation of the ladder line--seems a little high. Are you sure you don't mean 0.05 dB?

Walt

Does seem a little high. That what I got when I ran the numbers through the TLA program. The 450 Ohm ladder line is probably the 18 gauge type. The SWR is almost 14. I'll have to look at the graphs in the handbook and see what they say.

OH YEAH!!! Well ... I run an OCF with no tuner and a perfect match on 75m, 40m, 20m, 10m & 6m! It is the greatest antenna ever made and I am convinced it blows away anything you guys are talking about. That's what I've been told. YEAH!!! So there!!!!

Touchy feely ... what ... Who me?!

All the power in the world and I'm still PW!

God ... get me some real estate and some height and a nice dipole tuned for resonance and I might be able to strap W2VW for a change. Look out Dave.

John

Sorry John  but it will take a non-resonant doublet to strap my non-resonant one. BTW, I  live on an 80' X 100" seashore type lot.

Resonance means next to nothing in a doublet. Those who restrict their antenna(s) to resonant current fed designs are missing out on colinear gain and all band operation without a giant spider.

Make the most out of what you have......

So Dave, what are you running, since GFZ south is 60 by 175. My vee fell down in a storm so have to try something different. #8 feeders a bit too heavy.

Always remember PW is as PW does  ;D  ;D

I have been running a 60' flat top for years now and I'm not afraid to bounce bellies with just about anyone out there. No one complains about not being able to hear me.

You have to decide, do you want a REAL antenna, or some well advertized hocus-pocus designed to capture your wallet and not the aether!

Figure out what will fit your application best (lot size) and build an antenna that is optomized to minimise losses as best as possible. Design feeders to minimise I-R losses if you are running a short antenna. Put it up and STRAP! ! ! ! !

Also keep in mind: "Forward gain comes from the wall socket"  ;D  ;D  ;D

                                                                        The Slab Bacon

40 meter EDZ. One end has 20 feet dropping straight down at the end and there's an empty 40' X 100' lot next door. I'm using #8 feeders but have a center support.

The biggest disturbance ever in the Force occured in the mid-90's when Dean WA1KNX and the Derb met for the first time. They were taunted to do a belly bounce. Dino ran at Derb full speed - the Derb stood fast. After a tremendous explosion and some atom fusing, Dino bounced off into a heap to the ground. Derb had a stunned look on his face, while Dino was unrecognizable. It was gruesome and horrific to witness.

T

Dave, that would fit on my lot. Frank ant might require 4 supports. I will need a tram line to hold up the center though or have the center at 30 feet.What are your tuner settings on 160. Also how long are your feeders? Just so I have an idea of what it takes to tune it. I assume it has the cap on the balun side or is it series tuned.
My cousin Joe is having good luck with his 2X frank antenna.

ROFL...  That's true!

Another one I heard, when someone asked a local strapping station what the A in AM meant, he replies

Altitude
Amplitude &
Attitude


I had to paste your quote above on another site as a funny...  That's just too funny :)

--Shane

Tom,
        Myself and Big Mel (W3MB) did that at the Timmonium Hamfest some years back. It was a tough call who had the bigger belly, but both were pretty big. Another ham KA3UPR decided to be smart and put his head betweem the bellies as they came crashing together.
He was not only crushed to the ground, but his metal framed eyeglasses were crimped tightly to his face!  ;D  ;D

Feeders are just over 85 feet.

1885 I have just a little L in the pair and a lot of C across the feeders. Almost 2000 pf and about 2-1/2 turns 3" 6TPI. There's a lot of current there. I've paralleled some doorknobs because the vac variable only goes to 1500 pf. Any parallel doorknobs over 200 pf drift at QRO.

I installed a similar antenna at Rich W2OBR's place back when he had a signal on 160. Same deal there. We paralled 4 or 5 doorknobs. He has since gone back to an inverted L due to the price of admission.

29.000 is perfect with just a balun. That would make a good test of modeling. I'll get the exact numbers for 75 if you want but I need to ring out the coils first. 40 is unknown right now.

Dave,
The reason I ask is because I have 2 beautiful matched HD 12 uh roller inductors that would make a very nice tuner with a dual 450 pf 7000v johnson cap I have. My present 160 meter antenna is full sized with about 80 feet of feeders and wants all the l the fugly tuner can deliver 22uh..
Yes I would be interested in 75 to see if 12uh  is enough. I think they are 12 or 13 turns at 3 to 4 inch ID of heavy strap.

Frank,

      I've figured out settings for everyplace but 20 meters . 12 uh will be plenty with my wire lengths over my house. YMMV but the most I measured was on 7160 AND 3733 where it needed 11 uh. If yer coil won't do the job just homebrew a pair to place in series. Otherwise just drop the doublet and trim it like a JN with a fay-n dipole.

If you install the thing and trim the system to resonate at 29000 it should tune almost exactly the way mine does. 

TNX Dave, I bet the same tuner would work on Frank's configuration since his input Z is pretty low. The full sized antenna here just makes it with a pair of 22 uh. I tried to add some length and  it just got worse. I bet I would need ot add 60 feet to each leg to flip it over.

Frank isn't likely to change anything since he already gets excellent results.

A full size antenna with certain lengths of feedline will often leave some values in the shack which will need a whole lot of L as you know. Nothing wrong with that but it's strange that the shorty antennas with low radiation resistance often seem easier to match....until you pour on the coal :)

No I was saying if I went with Frank's configuration I should be able to match it.
I found you take the length of 1/2 a balanced antenna plus the feed line length and if it lands on a even quarter wave mulriple the Z is going to be pretty high needing lots of L. In my case here 125 plus 80 is getting close to 1/2 wave on 160 so it will take a good 60 feet to flip it the other way. I found this playing with rhombics years ago. As Frank says you need a real man's tuner to deal with low Z.

Walt, not Bill!  My apologies, must be the pain killers. :)


As always Walt(W2DU) is a voice of reason. The G5RV is what it is, as you describe. Thank you for your input. We hope you feel better soon.  

AB3AL,
IMHO, and reiterating some prior commentary, if you desire to go with resonant antennas and no tuner there’s little reason to not use coax for convenience. The losses won’t be that significant.  Moreover, you can feed all the antennas from the same single feedpoint (fan dipole).  I’ve used such a multi-band antenna for years and they work very well.

(W5HRO mentioned harmonic radiation being worse on 40 with a 75/40 meter fan, but his shortest element being cut for 40 would, like any 40 meter dipole, presents a good radiator for it’s 3rd harmonic anyway. If you have any harmonics above F3 you have other issues to deal with. So I don’t think that’s a valid argument against a fan dipole.)
 
 I use a W2DU style of choke balun at the feedpoint to reduce feedline radiation. This type of balun is not inclined to suffer from saturation since it is not a factor in the power transferred to the antenna. The inductance it presents only serves to choke off the unbalanced currents attempting to flow back down the shield. Since that current is being limited by the choke so too is the flux it produces in the core.  If you’re still worried about ferrite issues, a coiled inductor of coax works similarly, but less effectively

The multi band antenna I use (160-40) has it’s elements suspended parallel to each other using 5 ½” spreaders of ½” PVC.  Some people prefer to string the elements out like a fan, hence the term fan dipole.  

If you insist on maximum efficiency and must use open wire line, and don’t want to use a tuner, you must use an exact ½ wavelength of line to feed the antenna.  This will transform the impedance of the feedpoint to the transmitter virtually unchanged.  The SWR on the line is irrelevant, since open wire losses are so low. But this makes the feed system work on only one frequency (band) and defeats the purpose of the multi band antenna design.

There’s a lot of good info all over the web as well as from the fellas here. I have some info available on my web site on the multi-band antenna and balun applications as well. http://home.comcast.net/~msed01/amateur.html (http://home.comcast.net/~msed01/amateur.html)


Once you’ve weighed and understand all the factors involved you should have some decisions to make and a lot of us (unwittingly) do that subjectively. As long as you understand there’s no magic method, if it works for you…


73,
Mark

Mark,

FYI, W2DU is Walt, not Bill...

resonance is just a phase you are going through

My apologies Walt.

Anyone here ever get a 3 band "fan" dipole to work with low SWR on 3 bands.

I tried it in the past and it required a LOT of pruning. The 160 wire starts taking energy on 40 which is in parallel with the resin-aunt 40 meter wire.

My finicky plastic radio starts losing peaks above 1.2:1 SWR. 

Yes Dave, I have made several that play on three bands and more.  And, it's what I am using currently.

1.2:1 ?  That seems low. Did you ever notice that the SWR bridge in these rice boxes is usually much more sensitive to an inductive shift than capacitive (or vice versa, I can never remember which).  I readjust the protection level into the ALC circuit, it's too conservative. IMHO.

I never measured the J. All I know is peaks fall off very quickly with SWR over 1:1 on my ricer. I just spent 2 hours fooling with an amplifier tuned input to get it right. The ALC is already backed off somewhat.

I agree with the statement about resonance being a phase.. LOL.  Thats a good one :)

The main thing about antennas is that sometimes you get lucky and if it works, Leave it alone. I remember being on AM with Timtron till 4am one night. He switched between different dipole antennas to me.  He said 1, 2 3 4 so I had no idea what he was switching. One of them beat the others by a solid 20DB to arizona. I told him my findings, He laughed and said it was a G5RV he found in the Dumpster at a hamfest. He said he put it up for fun. It beat all the full size dipoles to me and a few others on the band that night.  They guys on the east coast said that the full size dipole was better. 

Sometimes no matter how hard you calculate and run the numbers, One antenna just works better at your location and band.

C