General Forums > Antennas
Double Bazooka antenna plans
W5LZ:
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
KE7TRP:
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.
W5LZ:
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
KE7TRP:
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
KE7TRP:
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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