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W5GI "Mystery Antenna"

Highlander_821

Highlander_821

Amour d'Ecosse
Apr 2, 2005
1,089
29
58
Central IL
Some of you may have seen my thread about this antenna in the tuners, etc category.

Here is a link to it: http://www.w5gi.com/mysteryantenna.htm

I just built my second one of these, gave the other to a buddy to try out. This second one is exhibiting similar specs to the other one, <2:1 SWR on 80, 40, and 20, and easily tunable on 17, 15, 12, 10, and 6.

This antenna is really amazing me. Marshall Islands on 17, Slovenia, Russia, Italy, and all over US and Canada and Caribbean on 20, Spain on 40 as well as all over North America. 80 meters works great, too.

All with just 100 watts and an MFJ tuner, often without the tuner. I just can't get over how well it works, and how relatively quiet it is compared to my Imax 2000.

www.thewireman.com has a kit or any of the components you might need to make one. If I can do it, ANYBODY CAN!!! This second one only took me 2 hours.

It is also a fantastic shortwave / mediumwave receiving antenna.
 

The W5GI is a phased 3 element collinear array on 20 meters. It also functions as a random length dipole on the other bands, just like a G5RV. It is made of wire and two matching sections of RG8x.


I'm not exactly sure what a double bazooka is, but it isn't a 3 element collinear.
 
Very basically, a 'bazooka' is a 1/2 wave fed through an impedance matching device made up of coax over the 'wire'. It's only 'plus' is that because of how it's 'fed' there is a very wide matching range. What isn't said about them much is that the further you are away from it's design frequency, the less efficient it is, but certainly gives a good SWR.
- 'Doc

[Reactance doesn't radiate, resistance does.]
 
Well I'm not sure ,but the double bazooka I think is defined as a doublt antenna maybe?

It uses coax or at least can be made from coax and a 300 ohm or 450 ohm twin lead on it's ends and it does not use a balun.

All I know is that They do have some that they claim can go from 80m-10m without a tuner.

I found them at Radiowavz.com They also had a windom antenna ; that I thought was very interesting.

I ordered one for a base I'm put up just to try it out, but it was specifically tuned for 11m.
 
You're right, a bazooka is a doublet antenna. But, a dipole is also a doublet antenna of 1/2 wave length. A doublet is defined as a length of wire (tubing, whatever) of undetermined length fed in the center. The biggest difference between doublet and dipole is that a dipole is a 1/2 wave length for whatever band. A dipole can be a doublet, but a doublet isn't necessarily a dipole (1/2w). That's 'accepted' terminology, not strictly definitive.
A bazooka/double-bazooka is a single band antenna which ~may~ have usable harmonic band usage. They are not an all band antenna by any means. Used with a tuner they may 'stretch' a ways. Without a tuner, forget it. Their biggest 'problem' is that since they are made with coax, they are heavier than just plain old wire or tubing.
- 'Doc
 
W5LZ said:
You're right, a bazooka is a doublet antenna. But, a dipole is also a doublet antenna of 1/2 wave length. A doublet is defined as a length of wire (tubing, whatever) of undetermined length fed in the center. The biggest difference between doublet and dipole is that a dipole is a 1/2 wave length for whatever band. A dipole can be a doublet, but a doublet isn't necessarily a dipole (1/2w). That's 'accepted' terminology, not strictly definitive.
A bazooka/double-bazooka is a single band antenna which ~may~ have usable harmonic band usage. They are not an all band antenna by any means. Used with a tuner they may 'stretch' a ways. Without a tuner, forget it. Their biggest 'problem' is that since they are made with coax, they are heavier than just plain old wire or tubing.
- 'Doc
Click to expand...



I guess It's just marketing when they say they can go from 80m-10m without a tuner then, or is it something in their design?
 
A bazooka is a single band antenna. Like any single band antenna they can sometimes be used on another band if that 'other' band is harmonically related. I don't think I would count on being able to use it on all bands unless I had some means of adjusting the input impedance that the transmitter will be working into. [That doesn't say anything about how 'well' it would radiate (radiation pattern) on those other bands, just how well the transmitter will like what it 'sees'.]
If the seller has really come up with a new design and not just a marketing scheme, I would tend to think that they would certainly be blowing horns about it (wouldn't they?), not to mention patenting the thing. Possible, but I kind'a doubt it.
The ladder line on the ends of a bazooka can be replaced with a single conductor or more coax. They are there because of 'end effect', or high voltage on the ends of half wave antennas, just makes things 'better', not as much 'de-tuning' because of the ends being close to something, or corona. The coax from the center to the shorted spots are tuning devices, like a 'stub' or gama-match. When you factor in the velocity factor of the coax used, those lengths of coax just happen to be resonant for the band the antenna is designed for (dang! There went all the 'magic'!). The same thing can be done with ladder line, but since the VF of ladder line is almost the same as plain old wire, those 'stubs' get much longer (sort of moves those 'shorting' points out to the ends of the antenna).
When a bazooka antenna was first being used they were radar antennas. They saw lots of use in Hawaii and that's where a great deal of the 'modifications' were done, the 'short end of the stick' sort of. Why use coax? Cuz that's what they had available without a lot of 'building' ('nuther one of them 'sort of' things). And like hams any where, when the military went to a different radar antenna and threw the old ones out, one of them hams wondered what he could use that fabulous piece of 'junk' for. Little adjustment here and there, and by-golly, it worked! They have their 'pluses' and 'minus's and if the 'pluses' fit what you want to do... Why not?
- 'Doc

Hmm... might be one reason you see them hams root'n around in dumpsters, huh?
 
The mystery antenna, depending on the lengths is essentially a dipole. The reason it is wide banded is because it has resistive loading components so as to keep the match within bounds through a wider SWR range.

One variety is a 'multi band' variant and that one is cut to be in-between more resonant points. This way the SWR is more tolerable across multiple bands.

The one rule to remember.

The wider the bandwidth of an antenna, it is almost a certainty that it is exchanging efficiency for that bandwidth. This mostly applies to commercial 'convenience' antennas. G5RV used out of band, Windom, B&W folded dummy loads, 'all band/no tune' verticals.

There's a fair amount to absorb for this to start making sense....I'm finally getting to where I look at antenna designs like a cobra and they begin to fail the smell test. I'm working on getting to where I can tell exactly what is wrong with them...though many will say that that is about the same as a golfer saying he is working on being a par player.

I can guarantee you one thing. A whole crap load of wire in the trees will certainly radiate better than 'no wire' in the trees. Get yourself a nice manual tuner and a spool of wire, the fun starts there.
 
W5LZ said:
[Reactance doesn't radiate, resistance does.]
Click to expand...

Is that a new law of physics?

my antennas don't seem to have much problem radiating when they are reactive.

radiation resistance in an antenna is the equivalent resistance that would have been used in an electric circuit that absorbed similar power to what the antenna radiates.
 

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