extended double zepp antenna questions

[loosecannon]

hi antenna gurus,

i have been studying this antenna design, and have seen some widely varying results, both in modeling and real world installs.

one says to feed with ladder line to an antenna tuner.
another says to use a 1:1 balun from the ladder line to coax, then to the rig, pruning the ladder line an inch at a time until a suitable SWR is reached.

if the antenna was intended to be used primarily on one band, (11m) would the balun method work well?

and what is the correct formula for figuring the length of the elements, and the length of the ladder line feeder?

i have seen a few different methods of figuring this.

one guy even said it would provide 11dbi on the band it was cut for.LOL
i find that hard to believe.

i believe the guy who says its more like 3db.

so, whats the scoop on this design?
anyone running one?

im thinking id like to have one up by the time the sunspots return.
loosecannon

 

[Master Chief]

If someone is looking for this type of antenna, don't look any farther than here:
http://www.radiowavz.com/html/c_b____11_meter.htm

OOPS! This is a double bazooka, not a double extended zepp! Still, its a great antenna for so many reasons!

 

[W5LZ]

An 'Extended Double Zepp' antenna is a center fed doublet, each side being 0.64 wave length for the lowest frequency of use. Or to make it a little simpler, it's a 1.25 wave antenna fed in the middle, that extra .02 of a wave length isn't gonna make any difference on most HF bands.
An 'EDZ is fed with a parallel feed line, not coax. That feed line should be an odd multiple of a 1/4 wave length at the lowest band of use. Even multiples of a 1/4 wave length on any band is going to be a problem. Using that parallel feed line also means that you should use a tuner, you'll need it. If the tuner can be fed with parallel feel lines then do so. If not, then use a balun. Coax from the balun to the tuner is possible but it should be as short as possible and a sort of 'heavy'/large coax. Any coax over about 10-15 feet is probably going to have problems.
An 'EDZ's 'gain' depends on what band it's cut for and what band it's being used on. It's a multiband antenna depending on how 'good' the tuner is. For the design frequency you can figure something on the order of about 3 dBi over a dipole, sort of. The higher you go from the design frequency (as in bands, not Khz), the greater the change in radiation pattern and gain. It doesn't have a 'continuous' radiation pattern, it has a number of 'lobes' which changes per band and location and the color of the sky probably.
It isn't a bad antenna, all things considered. It's one of those "higher is better" thingys. Won't be a lot of difference from a dipole (or any other antenna) is it's very low. Except for impedances and those are going to be 'fun' no matter what it's height. If you have the room, and can get it fairly high (1/4 wave is nice), they are fun to play with.
There are 'better' antenna choices depending on your available room to put them up in. Which can be said for just about any antenna, whoo-pee...
- 'Doc

 

[loosecannon]

thanks for the replies.
i will check out the bazooka antenna.

whatever antenna i choose, i wont have the room to really consider anything over 20 meters (bandwise).

i also cant set up any sort of decent groundplane.
the antenna will be strung across the top of a 24' high roof, (almost 50 feet across)needs to be stealthy, and if it was at all possible to feed it with coax, that would be ideal.

i am only asking the impossible, just like all the other unrealistic SWLs and hams out there.LOL

thanks for the advice, on goes the search.
it is fun and eduactional though!
did i mention i want to build it myself?
i have a real problem paying for wire antennas.LOL
loosecannon

 

[W5LZ]

"i have a real problem paying for wire antennas.LOL"
Believe me, I think I know exactly what you're saying. Something to think about when you run out of other 'stuff', is to see if you can latch on to a tuner somewhere. A fairly 'robust' one, if that makes sense. Then, try seeing what 'odd' things you can make radiate. Don't expect miracles! "Radio miracles" disappeared a long time ago, all used up, sort of. But you might be surprised at what can be an antenna. You probably won't be surprised at what won't make an antenna too .
- 'Doc

 

[SR385]

O.k. just a few things.

This will be a 'flat side' radiating antenna. Most people on CB are running verticals and as a result vertical polarization. For talking locally, your signal will be greatly reduced for anyone receiving with a vertical. For DX it won't make as much of a difference.

Something like this would work better chances are.
http://www.geocities.com/n2uhc_2/10m_dipole.html

This would be better yet.
http://home.comcast.net/~ross_anderson/sc.htm

Even better
http://web.telia.com/~u85920178/antennas/6dbvhf0.htm

Just have to do the math to size them for 11m center.

These were linked from here

http://www.ac6v.com/antprojects.htm

Also for playing with wire antennas a coupler/tuner would be very handy.

Lastly, dipoles if horizontal are directional. If you mount it pointing N/S the signal will actually get out E/W

 

[W5LZ]

SR385,
Dipoles being directional depends a lot on their height above ground. The lower ones are not any more directional than a vertical.
As for re-sizing a typical VHF/UHF antenna for HF, or visa versa, it's certainly possible! You might do the math before thinking seriously about it though - lol. They do get sort of large.
- 'Doc

 

[loosecannon]

thanks for the replies,

w5lz,

i know i need to get a tuner eventually.
its just that the house i most likely will be moving into very soon will only be my residense for about a year.
im hoping i can find something that will work without one for that period of time.
then comes home ownership, and trust me, a tuner will be a necessity there!

this antenna will only be used for 11m DX work, and SWLing.

the SWLing being the reason i am considering other possibilities besides the standard halfwave dipole.
a longer design can only help me here.

SR385,
the whole reason i am asking about these antennas is that i wont be able to put up a vertical antenna in my new location.
sorry, all your suggestions are out the window.LOL

i do not care one bit about losing some local comm. ability.
i can get out across my entire city with my mobile anyway.
hee hee...

i just want to be able to shoot some skip when it comes rolling in again.
yes, i know about how dipoles radiate.
i WANT it to radiate to the east and west, and not so much to the north and south.
because of my location, when the skip comes in, having a bit of a null to the south would be a good thing!
dont really care if i exclude a few people in canada.LOL

thanks for all the suggestions guys, i am now looking into folded dipole designs.
just cant decide.
good thing i dont have to yet!
loosecannon

 

[W5LZ]

loosecannon,
This is only for information and not for trying to discourage your interest in a folded dipole.
A 1/2 wave folded dipole has the same radiation pattern characteristics as the more common single wire 1/2 wave dipole. The only practical difference is in the input impedance. A folded dipole's input impedance can be figured if you know the spacing of the two wires and the diameter of the two wires. On the average about 4 times the input of a single wire dipole. Changing the diameter of one of the wires can make 'some' differences in input impedance, but not a huge one unless one of those diameters is made correspondingly huge. There are instances where that can be very handy (Mosley(?) used a folded dipole for the driven element on one of their beams).
The 'biggy' is that a folded dipole's radiation pattern, what it can hear, is the same as a common single wire dipole. No particular benefit, but no particular detriment in that regard.
If you want the 'formula' for figuring impedances for folded dipole it's fairly common, ought to be able to find it easily. Not sure how to write it correctly in this form posting (ASCII characters are not fully compatible, sort of) or I would list it. (not to mention that I'm just too lazy)
- 'Doc