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Author Topic: Double Bazooka Antenna  (Read 2077 times)
KG8JF
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« on: April 09, 2006, 06:52:07 AM »

I am thinking about erecting a double bazooka antenna.  Is it actually as broadbanded as predicted?  Does anyone have any idea as to the take-off angle campared to a half dipole?.  How does it play as a multiband antenna when used in conjunction with a good tuner?
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N3BIF
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« Reply #1 on: April 09, 2006, 08:10:55 AM »

 Mine worked OK but was no better than  a doublet of the same proportions feed with balanced line.  If you already have the tuner and wire simply put up a doublet.
     My bazooka was :
             heavy
             complex
             frail
             ugly
             time consuming to build
             no better then the doublet
             awkward
             not worth the effort

     Have fun making one perhaps your experience will be more rewarding.            
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WT0A
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« Reply #2 on: April 09, 2006, 08:49:14 AM »

A double bazooka IS a dipole, why would the take off angle be any different?
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RobertKoernerExAE7G
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« Reply #3 on: April 09, 2006, 09:25:55 AM »

http://www.qsl.net/we6w/ant0.html

http://www.soares.us/bazooka.htm

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KA4P
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« Reply #4 on: April 09, 2006, 09:49:19 AM »

I have a double bazooka on 160 meters. Yes, it is a big sucker. It covers almost the whole band. I have it cut for 1900KHz. The problem is that the SWR at 1900 is only about 1.6 to 1 (it is the best I have been able to do). On the good side it is also 1.6 to 1 at 1840 and also at 1970. The SWR starts to climb beyond either of those boundaries I mentioned but the wire is usable over the entire band without a tuner.

Technically the bazooka is slightly less efficient than a comparable dipole. I can't tell a real difference.
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WB2WIK
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« Reply #5 on: April 09, 2006, 02:13:11 PM »

When you get a low SWR across most of 160m with a double bazooka, that's not because it's a double bazooka; it's because the antenna's too low and you have a lot of ground loss -- I'd pretty much guarantee that.  Put the same antenna up 120' above ground, and see what the SWR curve looks like.

In theory, the "double bazooka" has ~17% greater BW than a conventional 1/2-wave dipole, and slightly lower efficiency (about 1 dB).  This data is published in almost every well-edited antenna handbook of the past few decades, and appears again in the ARRL Antenna Book 20th Edition.  At 17% greater BW, that means if a 1/2-wave dipole had 50 kHz BW on 160m (between 2:1 SWR points), then a double bazooka would be 50 kHZ + 17%, or 58.5 kHz.

Since a double bazooka employs shorted 1/4-wave stubs as the radiators, I don't see how it can work multiple bands.  It should be a single-band antenna.

And yes, I've built several of these over the years.  The first one I built was for 160m and we used it at a contest site where I hung it as an inverted vee from a 50' tower, and indeed it had a low SWR over the entire band!   Then, I found out so did a conventional wire dipole (260' long, half wave) installed at the same location.  It wasn't the double bazooka creating the wide bandwidth, it was the installation.

When we had a chance to install the same double bazooka on an arm off a 140' tower, it had a more normal SWR curve, with about 50 kHz bandwidth as expected.  Same antenna, less ground loss.

WB2WIK/6

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KB4QAA
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« Reply #6 on: April 09, 2006, 05:01:24 PM »

I am a great fan of the Double Bazooka antenna, having used one on 20M for years.   Actually I made and use a Crossover Double Bazooka, where your cross the center conductors to the shields at the center point.

- The DB antenna IS a dipole, so I would not expect any different take off angle compared to a regular wire dipole.

- The primary or perhaps sole advantage  of the bazooka is a wider bandwidth on the band it is cut for.  The bazooka has a very high Q or selectivity for that single band and is highly anti-resonant outside the band.  If you try to use it on other bands you will be converting most of your power to heat and reflecting a lot back into your transmitter.

- I have used a double bazooka as my main 20M antenna for years.  For reasons I have been unable to explain, that bazooka typically has better reception even on other bands, unmatched by other wire or vertical antennas specific to a band.

- Bazookas are not slap-together antennas.  You must cut, solder and seal carefully.  Mechanical strength is a weak point and every effort must be made to reinforce the joints and water proof them.

That said, I think the Double Bazooka is a wonderful if little appreciated single band antenna.

Good luck,  Bill.
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W5DXP
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« Reply #7 on: April 09, 2006, 06:13:40 PM »

http://www.w2du.com/r2ch18.pdf
--
73, Cecil, W5DXP
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
W8JI
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« Reply #8 on: April 10, 2006, 03:46:56 AM »

I made measurements of a Double Bazooka back in the 1970's when a fellow working for me started building them (at home) to sell at Hamfests.

We found the DB was no different than a dipole using the same thickness conductors as far as we could tell. It was not quieter, wider, or stronger.

The way we tested it was easy. We Installed two of them in open fields, and cut the center conductor where it crosses the insulator in one of them and tied it to the shield.

A few years ago someone sent me an IAC Double Bazooka for 80. I made more exacting measurements and compared it to a dipole. My results agreed very closely with the prediction in the ARRL Handbook, within a few percent.

The latest test showed a DB was no quieter than a regular dipole, had just a slight bit more loss, and only a slight bit more bandwidth. If I didn't have a network analyzer and reference antenna, I never would have known it from a dipole.

All that aside, how an antenna works isn't important.  How it makes everyone feel is everything. When I A B tested a dipole and a G5RV on 75 meters, everyone would say the dipole was better and say nice things about the dipole (like it had better audio). This was true even when I said I switched the antennas and didn't. When I called the G5RV a dipole, and the dipole a G5RV, nearly everyone reported the antenna I was calling a dipole (the G5RV) better than the antenna I was calling a G5RV (the same reference dipole).

My conclusion is if you want to use a regular antenna, pick a fancy name or an antenna with a good following and say that's what you are using. Your reports will be better, and you won't need to do all the work.

73 Tom
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N3BIF
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« Reply #9 on: April 10, 2006, 10:43:02 AM »

w8ji:  "My conclusion is if you want to use a regular antenna, pick a fancy name or an antenna with a good following and say that's what you are using. Your reports will be better, and you won't need to do all the work."

     Perception is  greater than reality . I love ji's observation.
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WB2WIK
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« Reply #10 on: April 10, 2006, 11:19:33 AM »

>All that aside, how an antenna works isn't important. How it makes everyone feel is everything. When I A B tested a dipole and a G5RV on 75 meters, everyone would say the dipole was better and say nice things about the dipole (like it had better audio). This was true even when I said I switched the antennas and didn't. When I called the G5RV a dipole, and the dipole a G5RV, nearly everyone reported the antenna I was calling a dipole (the G5RV) better than the antenna I was calling a G5RV (the same reference dipole).<

::I like the idea of better audio.  Do you think if I use oxygen-free copper wire I can get better audio out of my antenna, or should I go for gold plated?
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WA2CWA
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« Reply #11 on: April 10, 2006, 02:52:50 PM »

My wire dipole, a deluxe DX Extreme, is made from pure, oxygen-free copper; low noise and a magnet for DX signals. I swear by it.

Pete, wa2cwa
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WB2WIK
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« Reply #12 on: April 10, 2006, 04:01:42 PM »

Pete, have you tried DB GREASE on that?  Signals just slide right down the wire, faster.

I call my wire the Ionizer Special, it opens the band even with no sunspot activity.  For a bit extra, you can upgrade to the Ionizer Special Plus, pending approval for sale in the U.S., but already legal for export.
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WA2CWA
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« Reply #13 on: April 10, 2006, 05:01:19 PM »

Steve said:  "Pete, have you tried DB GREASE on that? Signals just slide right down the wire, faster.

I call my wire the Ionizer Special, it opens the band even with no sunspot activity. For a bit extra, you can upgrade to the Ionizer Special Plus, pending approval for sale in the U.S., but already legal for export."


I haven't tried DB GREASE yet, but I heard it really gives the big contest stations the edge. Got to get some when I go to Dayton this year. Also plan to coat the 6 meter beam elements with it. With band openings sometimes very short, get the signal faster to the rig is a real plus.

Pete, wa2cwa
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KB3LXY
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« Reply #14 on: April 11, 2006, 06:42:21 AM »

...Hmmmm?
Well my Zep has "Rf adjudicator" fins added. Very trick !
Smiley
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