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Base Double Extended Zepp

LeapFrog

Wielding Hanlon's Razor
Feb 15, 2016
1,709
903
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Anchorage, Alaska
I am thinking about making a Double Extended Zepp antenna for CB.
I'd like to be able to get away without using an antenna tuner. (don't have one)

I am thinking of using: two 0.64 wave length elements fed with either
450 Ohm ladder line with a 9:1 balun for 450 ohms to 50 ohms coax.
Or
600 Ohm ladder line with a balun 12:1 balun for 600 ohms to 50 ohms coax.

Has anyone tried this, & what kind of matching network or feed line would you use 450/600 Ohm?

Am I missing anything here? My goal is to get some gain over what a traditional half wave dipole would offer, w/out using a tuner.
extendeddblzepp.GIF

Thank You, I can find a calculator online for the element lengths, I'm curious about matching (50 Ohms)..
 
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Hi Leapfrog:

Check these designs,you could use the matching idea from the Saturn

Credit to the Authors
 

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I think what you are missing is that the ladder line is acting as an impedance transformer and may not be anywhere near 450 or 600 ohms at the end you plan to connect the balun to. It will vary with antenna and feedline length.

It will repeat the impedance of the dipole feedpoint every half wave along the ladder line. That's electrical half wavelength. If you were to feed that 50 ohm dipole with a 1/4 wave length of ladder line you would have a high impedance at the balun or tuner. If the dipole impedance were high you would have a low impedance with that 1/4 wave of feedline.

I don't know the math to get you where you need to be so I'd have to resort to an online calculator and possibly some guess work.

If you go the tuner route don't buy one. Most tuners on the market absolutely suck for feeding balanced line. They will likely cause an imbalance on 11 meters and the feedline will radiate. You've probably got the stuff laying around to throw together a balanced L. Roll 2 identical coils, find a variable cap and add some good test clips. It doesn't need a case.
 
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Run ladder line all the way and add a balun in front of that tuner and it'll take care of that 'imbalance' problem. If you have a fairly 'broad' tuner you can make it work just dandy.
 
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Run ladder line all the way and add a balun in front of that tuner and it'll take care of that 'imbalance' problem. If you have a fairly 'broad' tuner you can make it work just dandy.

He'll still have an unbalanced tuner with a balun. He will also have to pay attention to feedline length so he doesn't have high impedance at the tuner or balun. (Anyone burning up baluns and don't know why?) This is even more important if running power. It would be better to skip the tuner, use the extended double zepp calculator, use the required balun. He's only using the 11 meter band.

If he could find the sweet spot he could feed the ladder line with coax and a 1:1 balun or a simple coax choke. I have a doublet that accidently turned out to be an edz for 17m. A coax choke and about 70pf across the connector on the radio side of the choke makes a perfect match.

Leapfrog is a smart guy. If he ever needs a balanced tuner theres no reason for him to settle for a ham store tuner that cost too much. I've built a balanced L and link coupler tuner. I will not go back to the T match and balun again. No more RF problems in the shack and people seem to hear me better.

Window line sucks when it gets wet. Homemade ladder line spaced wider with as little material possible between the leads will have less loss and minimal changes in tuning on a rainy day.
 
He'll still have an unbalanced tuner with a balun. He will also have to pay attention to feedline length so he doesn't have high impedance at the tuner or balun. (Anyone burning up baluns and don't know why?) This is even more important if running power. It would be better to skip the tuner, use the extended double zepp calculator, use the required balun. He's only using the 11 meter band.

If he could find the sweet spot he could feed the ladder line with coax and a 1:1 balun or a simple coax choke. I have a doublet that accidently turned out to be an edz for 17m. A coax choke and about 70pf across the connector on the radio side of the choke makes a perfect match.

Leapfrog is a smart guy. If he ever needs a balanced tuner theres no reason for him to settle for a ham store tuner that cost too much. I've built a balanced L and link coupler tuner. I will not go back to the T match and balun again. No more RF problems in the shack and people seem to hear me better.

Window line sucks when it gets wet. Homemade ladder line spaced wider with as little material possible between the leads will have less loss and minimal changes in tuning on a rainy day.

I appreciate your help 543,
I think I still have an old rotary variable capacitor from an early "E.F. Johnson CB Matchbox" laying around somewhere.
I think that would work just fine, and i'll use 1/2 wave length of "low loss" 50 Ohm coax!

Run ladder line all the way and add a balun in front of that tuner and it'll take care of that 'imbalance' problem. If you have a fairly 'broad' tuner you can make it work just dandy.

Paul-W5lz, thank you for the suggestion, I'm going to mount the "tuning capacitor" outside, I will not be using a conventional tuner in the shack.
The 50 Ohm coax will travel outside to the "bottom of the antenna" where the coax will meet the ladder line at the feed point.


Hi Leapfrog:
Check these designs,you could use the matching idea from the Saturn
Credit to the Authors

I'll translate the Italian w/ Google, I I appreciate the files and the links there brother.


All things considered, I think this could be built and made to work for about the price of a decent omnidirectional vertical!


I'm beat gentlemen, I've had a full day. I'll revisit the thread tomorrow to share some links I've found.
I Hope you all have a great evening. Thank you :cool:
 
Why the half wavelength of coax? When I was talking about feedline measurements I was taking about the ladder line. If whatever you use for a matching device gives you somewhere in the ballpark of 50 ohms the coax length to the transmitter doesn't matter.

There is a formula in this article to calculate the voltage at the end of the feedline If you calculate the impedance at that point. Useful in a lot of applications.

http://www.somis.org/bbat.html


Another idea would be to hang a matching device at the apex of the dipole and run coax all the way. Once you find the values you need it can be built with fixed value caps and compact.
 
Why the half wavelength of coax? When I was talking about feedline measurements I was taking about the ladder line. If whatever you use for a matching device gives you somewhere in the ballpark of 50 ohms the coax length to the transmitter doesn't matter.

There is a formula in this article to calculate the voltage at the end of the feedline If you calculate the impedance at that point. Useful in a lot of applications.

http://www.somis.org/bbat.html


Another idea would be to hang a matching device at the apex of the dipole and run coax all the way. Once you find the values you need it can be built with fixed value caps and compact.

543_Dallas, I'll probably use the least amount of coax I can get by w/ using, and run the low loss ladder line "up the tower & to the shack", I can see if my variable air cap will work, I
Thank you for the link to the article and for the great suggestions.
 
I once did exactly this for cb.
I made the extended zepp dipole and made a homemade open wire twin lead of a given length that was is own impedance transformer. From the transmitter end of the twin lead I just attached the coax on to the radio. Worked fine with good SWR.
0076_zpsbbcd3563.jpg 0073_zpsfe53f0bf.jpg
 
I once did exactly this for cb.
I made the extended zepp dipole and made a homemade open wire twin lead of a given length that was is own impedance transformer. From the transmitter end of the twin lead I just attached the coax on to the radio. Worked fine with good SWR.
View attachment 21368 View attachment 21369
Looks to be about a 1/2 wave high, how well did it work?
- Also, I'm curious what impedance value you perceived at the feed point of the doublet?
 
Xway too long ago to remember any of it. Lost the info on a crashed PC.
I do recall. It picked up too much noise from within the house that close ti the attic. Had a great SWR at the transmitter.
 
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How did you calculate the feed line length needed homer? I haven't quiet wraped my brain around it and most of the online calculators require a 4:1 balun if you use their measurements.

Dumb luck allowed me to have an edz for 17m. The doublet is about 70 feet long the feed line is roughly 35 to 40 feet of #8 with 4 inch spacers. With a simple coax choke and a 68 pf cap across the so239 on the radio side of the choke it is perfect on the phone portion of 17.
 
How did you calculate the feed line length needed homer? I haven't quiet wraped my brain around it and most of the online calculators require a 4:1 balun if you use their measurements.

Dumb luck allowed me to have an edz for 17m. The doublet is about 70 feet long the feed line is roughly 35 to 40 feet of #8 with 4 inch spacers. With a simple coax choke and a 68 pf cap across the so239 on the radio side of the choke it is perfect on the phone portion of 17.
I don't recall. Lost the info I had with a crashed PC. I'll try to find it again and share it.
 
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Another
zeppelinfigura1.jpg

Legs length - 6' 1"
Radiator wires length - 21'
Top space - 15-3/4"

Haven't tried this. Someone may model it to verify. If it stinks we'll know.
 
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