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Author Topic: Double Bazooka antenna plans  (Read 25063 times)

KE7TRP

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Double Bazooka antenna plans
« on: July 09, 2013, 08:38:01 PM »

I just got this info from a friend of mine. They built this antenna and he said it does cover the entire 80 meter band under 2 to 1.  His signal is stronger then his old wire and he no longer needs the tuner.  I thought I would post this info up in case there are any other antenna experimenters out there.

C
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W5LZ

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Re: Double Bazooka antenna plans
« Reply #1 on: July 10, 2013, 06:45:22 AM »

I don't doubt your friend's findings, but you have to keep in mind that they are subjective, not objective in nature.  A bazooka antenna does have a wider 'apparent' usable band width, but only at the lessening of efficiency the further you get away from it's 'design'(resonant) frequency.  As the frequency range increases from it's design frequency the efficiency of the antenna lowers because of reactance present in the antenna because of it's method of being 'fed'.  Reactance doesn't radiate anything, it contributes to a 'dead' loss in radiation.  The means of measuring SWR, a typical SWR meter can't distinguish between 'R' and 'X' (which combined equals impedance).  The SWR meter 'sees' a combination of 'R' and 'X' that it 'thinks' equals 50 ohms impedance, but doesn't mean 'R=50' and 'X=0' at all.
Why does it seem like an improvement over his wire dipole?  Because of how he's measuring things, using an SWR meter.  Those things are just not very 'accurate' in measuring radiation efficiency, just impedance matching.
 - 'Doc
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KE7TRP

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Re: Double Bazooka antenna plans
« Reply #2 on: July 10, 2013, 08:14:50 AM »

I agree.  There is no free lunch Doc. 

What do you think about the loss of say a standard 80 meter dipole stretched to cover the entire band using a typical T match tuner, VS, having the Bazooka antenna with no tuner?

A typical dipole will have 150 KC of usable bandwidth before you must go to the tuner.   

I enjoy experimenting and testing out different antennas so its all fun to me!

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W5LZ

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Re: Double Bazooka antenna plans
« Reply #3 on: July 12, 2013, 05:04:44 AM »

In general, meaning that there are a lot of variable in that sort of comparison, I think it'd probably work out about even.  Both are 1/2 wave antennas so the difference in 'performance' isn't going to be that different.
I don't mind using a tuner and have for a long time.  I'm not too 'fixed' on having a 'perfect' antenna system, I've found that one that isn't exactly 'perfect' will do just as well in some cases.  That tuner can also make an antenna 'usable' on other bands, sort of, you know?  Tuners aren't a 'cure-all' but they can make things easier...
 - Paul
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KE7TRP

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Re: Double Bazooka antenna plans
« Reply #4 on: July 12, 2013, 09:45:46 AM »

I agree Paul.  I enjoy working with antennas and plan to try a few different styles.  I just wish it was not july in Arizona.. Its to hot to even go outside, yet alone, work on an antenna.

C
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K3DAV

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Re: Double Bazooka antenna plans
« Reply #5 on: July 13, 2013, 09:57:40 PM »

I have built several Bazooka antennas in my past, and I have to honestly say that every one I built out performed the basic wire dipole it replaced.  A lot of how they perform depends on the materials used in the construction.  ie type of coax, type of wire used for the tails, and even down to the kind of solder used on the connections.  And one big mistake that many guys make when building a Bazooka is the exact measurements on each side of the feedpoint. 

Too many times, guys just do a rough measurement and one side turns out to be a few inches longer than the other.  They do the same with the tails when trimming for SWR.  This makes it impossible to get a good low SWR across the band.  You have to make the measurements exactly the same on each side of the main element and on the tail trimmings.  It is how you get the best impedance balance over the entire length.  If these aspects are paid close attention to, a Bazooka will outperform a dipole every time. And yes it is possible to get a 1.1 SWR in the band center and as low as 1.4 SWR at the band edges.  I have proven it time after time.

Another mistake is the type of coax used to make the antenna.  Using any kind of coax with a double shield or a foil lining around the center conductor, actually lowers the performance.  A Bazooka is designed to work best with leaky type coax.  The only 2 coax types that should ever be used to make a Bazooka are RG-8X and RG-8U.  Basic RG-8X (Mini) works very well on almost any HF band.  But the basic standard RG-8U coax works better.  The main reason is due to the larger diameter of the RG-8U shield wire.  The larger diameter wire provides a wider bandwidth for better SWR at the band edges.

I built a Bazooka with RG-8X for a friend to use on 60 meters.  I cut it to the center frequency of the 5 channel spectrum.  The SWR does not go above 1.2 at the edges and a 1.1 in the middle.  He has had great contacts around the country and into Europe and Asia with it.  Build the the right way and they will work the right way.


I have an article on my website that explains the details a lot better than I could do here.  Anyone wishing to read my article can CLICK HERE
« Last Edit: July 13, 2013, 10:11:46 PM by K3DAV »
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W5LZ

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Re: Double Bazooka antenna plans
« Reply #6 on: July 14, 2013, 05:36:01 AM »

Here are some observations I've noticed about bazooka type antennas.
It's a 1/2 wave length antenna and will behave/radiate as any 1/2 wave length antenna will.  It will be
have the same radiation pattern and be affected by all the things any such antenna is affected by,
height above ground, whats around it etc.  The biggest difference is in how a bazooka antenna is fed.
It's fed through a tuned circuit, a lot like a 'beta' or 'delta' match.  That feeding method is why it has
such a 'wide' usable SWR range.
What type of coax cable used in the construction can make a huge difference in performance.  Coax with
a 'foam' type insulation will not handle the higher voltages present as well as a cable that uses a 'solid'
type of insulation.  So, RG-8X isn't a great type of cable to use for a bazooka antenna.  (A voltage increase
is always a product of impedance transformations.)  The old RG-8 type cable with solid inner insulation
tends to work better.
The old 'classic' bazooka with the open wire feed line type 'ends' uses those larger 'conductors' because of
end-effect, high voltage at the ends of a 1/2 wave antenna.  Makes for less arcing, corona discharge. 
Considering the intent of the original bazooka antenna, radar, which involves high power 'pulses', corona
discharge was a real problem.  With typical amateur use those large conductor 'ends' aren't really needed.
You can still use them, won't harm a thing if you do.
The type of coax used in it's construction will also determine the different lengths of various parts of a
bazooka antenna.  The overall length will stay pretty much a 1/2 wave length, but the lengths of those
center sections, the tuned circuits, will be affected by the velocity factor of the coax cable used.  Those
center section lengths (electrical 1/4 wave lengths) are affected by the velocity factor of the cable, making
them 'shorter' than the full length of 1/2 of that antenna.  That's why they are shorted toward the ends of
the antenna instead of just continuing to the ends, 'tunes' those center sections, right?
So why don't the 'numbers' work out exactly?  Because there are a lot of variations in coax cable, none of
it is ever exactly the same on the same spool, much less the same manufacturing 'batch'.  See how that
affects things?
Performance or efficiency is determined by what you are measuring with.  A bazooka antenna is not very
efficient away from it's design or center frequency.  A typical SWR meter is a terrible means of measuring
performance or efficiency.  At best, an SWR meter can only indicate how well impedance matching is done
which has very little to do with how well an antenna 'works', how it performs.  A dummy load is a very good
example of that, great SWR, lousy antenna.  If your main criteria is SWR then a bazooka antenna is a very
nice antenna to use.  If it serves your purpose well, then use one!  There still ain't no such thing as a free
lunch, but if the price isn't too steep, why not?
 - Paul
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K3DAV

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Re: Double Bazooka antenna plans
« Reply #7 on: July 14, 2013, 06:32:54 PM »

I agree with most of what you say Paul.  The Bazooka is subject to the same conditions as a dipole for height above ground and the surroundings.

But one of the main points I was making is how guys build these antennas and do not pay close attention to the measurements.  If one side of the main element or the tails are off even 1 or 2 inches from the opposite side, the antenna will not operate with the best efficiency it should give.  That is a mistake I learned the hard way the first few times I built one.

But I have to say that the Bazookas I have built did a better job than their late dipoles they replaced.  Now there has to be something to that.  For example, I helped a friend build a basic dipole for 40 meters several years ago.  He runs only the 100 watts from the radio.  We were extra careful of the measurements, and used my MFJ-269 analyzer to tune it before it went into operation.  It worked very well for my friend always with great reports.

Then I built him a 40 meter Bazooka.  Tuned it again with my MFJ analyzer, then put it to the test on the air.  The Bazooka was strung in the exact same space the dipole used to occupy, so height above ground and the surroundings were the same.  The first thing we noticed was the background static was lower which made us think the antenna was not quite as good.  But the locals noticed his signal was higher, and the receive signals were higher also.  And then the DX test.  My friend here in PA talks on a 40 meter net every afternoon.  The net controller is up in CT which is about 250 miles east with 100 watts in the daytime on 40 meters. The net controller noticed the increase in signal instantly, and the same over the next few weeks.  The same improvement was noticed by most of the operators on the net also.

For what it's worth, the analyzer said the impedance was 43 ohms at the lowest band edge and 59 ohms at the highest band edge, but it was 51 ohms in the center where we tuned it to a 1.15 SWR.  I have never found a basic dipole that could do that well.  Many can get a good 49 to 51 ohms at the band center, but drop to 30 or lower at the low band edge and to 75 at the high band edge.  The tuner was never needed on any frequency within 40 meters.

The lower noise level is probably due to the DC grounding effect by the continuous loop type connection of the center wire.  This usually helps reduce typical QRM and QRN on any DC ground antenna.  The SWR was lower on each band edge which at least helps the radio run a bit more efficiently.  But the fact is, the design of the Bazooka does create a slightly larger signal pattern than the average 1/2 wave dipole.  This actually produces a tiny amount of gain.  It's not much, but even a 0.2 dB gain is more than 0 dB gain.  It may not be a big bad increase in the ERP, but it does make the signal pattern larger which directs a bit more of the signal towards the horizon.  Again nothing to write home about, but it is noticeable.  Any increase no matter how big or small is still an increase over what it was.  This only proves that not all 1/2 wave antennas radiate the same exact way.  If you notice the actual length of the Bazooka actually measures less than a 1/2 wave.  But the design gives it a larger radiated pattern than a 1/2 wave dipole.

All I can say is that I must have made more than 50 Bazookas in my time, and those that replaced basic dipoles outperformed the dipole.  Some were made with RG-8X and some with RG-8U.  The RG-8X should be able to handle the same power it is rated to carry.  If that is the case, then RG-8X should handle full legal limit on any HF band.  The power rating drops big time for VHF and UHF so I would not use the 8X on those bands.

I am only reporting the results that I have gotten with the many Bazookas I have built.  But I know guys who have seen the same observations you have with their own built Bazookas.  I still believe from good experience that those who get less than expected results, have built the antenna with measurement errors and did not notice them or even think to check them.  As I said I found out the hard way how crucial those exact measurements are between both sides from the feedpoint.  But now I know better and I pay very close attention to the measurements of each side.  If the Bazooka is built correctly with the right measurements and materials, it will indeed outperform any basic dipole.
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KE7TRP

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Re: Double Bazooka antenna plans
« Reply #8 on: July 15, 2013, 08:34:33 AM »

The bad press on the bazooka comes from a foreign ham who ran tests on dipole vs his homemade bazooka.  His tests show a major loss in performance and in short, Slammed the antenna.  Ham read this and just parrot what he wrote.  I try to run my own tests here and will as soon as I get my antenna up in the air. I plan a back to back test with two antennas up at the same time. 

Recently two stations I know switched from wire to the bazooka and both have stronger signals here and they don't have to use the tuner anymore.  If this antenna does not work as well as my wire, I will report it and I will find the drawback. 

C
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K3DAV

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Re: Double Bazooka antenna plans
« Reply #9 on: July 15, 2013, 08:04:31 PM »

Ahhhh That explains a lot.  Have you ever read reviews for anything on Eham.net?  There are usually a majority who loves or hates the product.  But nine times out of ten, those who are in the minority who hates something, usually did not construct or install the product properly.  This is more so with antenna reviews.  When a vast majority love the antenna, and a few hate it, it's usually because the haters built it or installed it wrong.  And you know they would never come back and say, "Ooops I made a big mistake and now I love the antenna."

Well Clark, I eagerly await your test results, so get out in that Arizona hell heat and get to work.  LOL
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W5LZ

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Re: Double Bazooka antenna plans
« Reply #10 on: July 16, 2013, 05:19:54 AM »

In one of the early ARRL 'Antenna Compendium' series a very extensive series of tests were done on the bazooka antenna.    It wasn't 'on the air' type testing, but measurements done as on an antenna test range.  There were quite a few variations in the antennas tested covering feeding methods and I honestly don't remember what else.  My copy of that 'Compendium' (#2 I think?) has disappeared over the years so I can't cite it, rats.  The article was done by a well known author, can't remember his name though.  It would make for interesting reading...
 - Paul
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KE7TRP

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Re: Double Bazooka antenna plans
« Reply #11 on: July 24, 2013, 07:42:54 PM »

I got my 75 meter DBZ up today.  Mine is made from RG11 coax.  I am not getting the bandwidth I wanted.  I can go from 3715 to 3915 under 2 to 1. Not the whole band.  I am using 100ft of Brand new LMR400 for the feedline that then runs into 100 FT of half inch hard line.  Tomorrow I will run the LMR into shack so I will remove 100 FT of feedline. 

The tests ran tonight where back to back. It took me 2 minutes running to lower 80 meter Open wire line antenna and put up DBZ.

The setup:


55ft crank up tower set at 40 ft due to monsoon season.
Antenna 1 = 126ft open wire line doublet (True ladder line dot com) to a Johnson matchbox balanced tuner. 40 ft
Antenna 2 - Double bazooka made from RG11 coax fed with LMR400. 35 ft

5 stations on the air ranging from 15 miles to 400 miles..  NOBODY knew which antenna I was on. Only Antenna 1 and antenna 2.

In all cases the DBZ BEATS the Doublet.  I am in shock.  I would have bet money the open wire doublet would win.  Reports are 3 to 6 DB.  I see 6 DB lower baseline noise on my band scope with the DBZ. But 3 to 6DB higher RX. 

Keep in mind I ran out and switched the antennas back and forth and did the tests 4 times.

NOT one station said Antenna 1 was better.  NOT one station was higher on RX then Antenna 2.

The DBZ on these state side contests wins with out question.  Now to ponder why.  There nothing much more efficient that 600 ohm open wire line to a doublet with a balanced tuner.

Tomorrow I will remove the 100 Ft section of hardline and run just the LMR400.  I will also put the DBZ at 40 ft.  Then, I will adjust it for 75 meters. The Low point is 3800 where I would like 3900.

The best part of all of this?

With the Open wire line doublet, If I ran 100 watts, I would blast over the Home theater.  With the DBZ, I can run 100 watts and not cover over the theater at ALL.  In fact, I can run up to 500 before I just start to hear my signal over the speakers. 

Hmmm.   I had a lot of fun with these tests.   More to come.

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W5LZ

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Re: Double Bazooka antenna plans
« Reply #12 on: July 25, 2013, 06:46:30 AM »

Most of the 'playing' with a bazooka antenna was before 'eHam' or the other review sites were around so I can only go by what I've read and experienced.  Almost all of that 'testing' was done on 80 meters, that's where I hung out, and there were others there that used a bazooka type antenna too.  I have to say that this sort of 'testing' was subjective, not objective in nature.  I certainly didn't have the equipment and antenna range to do a really objective type of test.
Antenna comparison testing is very difficult to do objectively, there are just a huge number of variables involved in that and they can 'go' either way good/bad.  'On-the air' testing has got to be one of the most unreliable means of testing antennas.  What if there's no one listening, what if there's too many listening?  Anything around an antenna can affect how it behaves, so how can you have two antennas up at the same time, on the same band, and they not affect each other?  That doesn't mean that I doubt what you experience doing this sort of testing!  It does mean that it isn't exactly a 'take it to the bank' sort of test.  It's subjective.
If a particular type/style of antenna works for you then by all means use it. 
 - Paul
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KE7TRP

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Re: Double Bazooka antenna plans
« Reply #13 on: July 25, 2013, 08:57:26 AM »

Thanks for posting Paul. Yes, We do not have an antenna range. I wish we did. However, We can compare antennas at home.  That's a great part of the hobby that I enjoy.

I only had one antenna up at a time.  The second antenna was in a pile under the tower between tests.  I tested 4 times back to back.  In all cases, my chart has reports of higher signal on the DBZ. My Chart shows higher RX signal that is in line with the gain in TX.  I would not have believed this if I was not there.  It really makes no sense to me as the Open wire doublet should have next to no loss through a balanced tuner.  However, There must be some loss somewhere or the patterns are such that in state contacts suffer on the doublet. 

I think once I do my tests over a 2000 mile distance, we will have more data.  Its possible that the Doublet has a strong vertical component.  If so, Then this all makes sense. The close in under 500 mile contacts are going to be better on the DBZ.  More of an NVIS pattern.

Using a Field strength meter at 25 watts AM carrier there is no detectible RF on my Feedline of the DBZ. On the OWL, of course the meter pins near the feedline.  I have current meters on each leg of the doublet and It is in balance with in a % or so.  Even then, You do have some RF off the OWL.

The DBZ does not come over the home theater which is a great plus in my household.  I think this is because the DBZ is not radiating over the feedline and causing the interference.  There is also the idea that the OWL with balanced grounded tuner, Is using the HOUSE wiring as a counterpoise.  Hence, The home theater turns into a public address system.

I was going to run some more tests today but woke up to pouring rain.

C
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KE7TRP

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Re: Double Bazooka antenna plans
« Reply #14 on: July 26, 2013, 10:19:34 AM »

I got the 40 meter DBZ installed.  I compared this to my 80 meter open wire line fed doublet yesterday. Both close to same height.  On 40, The 80 meter open wire line antenna has gain.  About 3 DB according to EZnec. I am using a Johnson KW matchbox with the open wire line.

Base line noise level is approximately 4 to 5 DB lower on the DBZ. I used my SDR pan adapter to show the static noise at various frequency's across the band.   

Peak signals from Foreign Broadcast where exactly the same. I could not prove one was better than the other. I then proceeded to make a page of 40 meter contacts across the US. Not one station reported one was better than the other.  I could switch between words with NO delay.  Over the course of the day, stations just reported that they are the same.

The SWR on the analyzer shows 1.0/52 ohms at 7200 where I set it.  Its under 1.5 across the entire 40 band.  No tuner needed.   

The 40 DBZ does not come over the Home theater.

Looks like a great antenna for 40 meters.

C
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