resonant antennas and open wire line

[W2VW]

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......

[WA1GFZ]

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.

[The Slab Bacon]

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

Always remember PW is as PW does   

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"     

                                                                        The Slab Bacon

[W2VW]

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.

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.

[K1JJ]

... and I'm not afraid to bounce bellies with just about anyone out there.
                                                                        

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

[WA1GFZ]

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.

[KD6VXI]

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

                                                                        The Slab Bacon

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

[The Slab Bacon]

... and I'm not afraid to bounce bellies with just about anyone out there.
                                                                        

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

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!   

[W2VW]

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.

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.

[WA1GFZ]

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.

[W2VW]

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. 

[WA1GFZ]

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.

[W2VW]

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

[WA1GFZ]

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.

[KA2QFX]

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


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

[Ralph W3GL]

Mark,

FYI, W2DU is Walt, not Bill...

[WA1GFZ]

resonance is just a phase you are going through

[KA2QFX]

My apologies Walt.

[W2VW]

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. 

[KA2QFX]

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.

[W2VW]

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.

[ke7trp]

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