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[KB6HRT]

Am testing a 40m DB antenna built with RG11 coax, it works very well, have tested it against a very good 75-40m dipole that I built using a 1 to 1 balun at the apex and my 450 ohm LL fed dipole. The DB seems to have less noise on very low signals on A-B-C comparisons, on strong signals its peaks are higher, on receive the average signals are clearer, this is the criteria I am looking for plus  RG11 is stronger than RG6 so should stand up better in the winds we get here in the Spring, Any comments on DB antennas would be appreciated..................kb6hrt

[JS6TMW]

YOU MIGHT WANT TO LOOK AT A CURRENT DISCUSSION OVER ON QRZ FORUMS.  Lots of strong opinions over there but they should welcome your real-life results.

[KD6RF]

Bless ya man for having fun comparing antennas!

The rub is that you are giving “impressions” rather than numbers, and those can  be misleading !!!  

There is much written about bazooka – you can just google and find multiple sources on it’s actual principle of operation.    edit ==> like the discussion mentioned above...

The quick version – It’s nothing but a standard dipole, with a section of coax that may have a small bit of broadbanding due tiny reactance cancellation and larger diameter, but mostly due to the lossy-ness of the coax.

Other than the bit of loss, it is not quieter than a dipole, because it IS a (somewhat lossy) dipole.

It does not have higher “peaks” than a dipole , it has slightly lower “peaks”, because it IS a (somewhat lossy) dipole.

And it is no more or less “clear”, than a dipole, because it IS a (somewhat lossy) dipole.

Any differences you may or may not be perceiving are due to some combo of orientation, location with respect to noise sources, height, or some other physical orientation factor that differs between the bazooka and your dipole(s).


In general, bazooka is pretty much heavier and mechanically inferior to your more robust dipoles, but without any significant performance advantage.

[JS6TMW]

The above comment is just about the whole gist of that QRZ discussion, and I have read others where proponents and opponents argue over the DB with theological fervency. KD6DF is certainly right that brief comparisons are not especially conclusive. I think they need to be done over a fairly long time period with good accuracy. I am right now trying to compare 2 different shortened 40-meter dipoles and have quickly learned that "noise" comes from different sources and directions, and these vary over time. Just when I conclude that one antenna is "better", the next night I can change my mind.

[KB6HRT]

Please take this post for what it is, am not trying to sell anyone anything, it my finding so far, time will shed more light on this project I am sure............I love this stuff,  been doing radio things like this almost 50 years now. Only thing I do know is, I have to get out an actually do this stuff myself so I do know what I am talking about best I can. So far have used different types of coax for different 40m DB, all have rendered different results. Have tried different angels of the the inverted Vee did raise an lower the antenna to get the SWR where it worked best with my equipment, reverst the antenna 180 deg to see if there was a preseaveable  difference against the reference dipoles,  have a lot more testing will be doing over time.

[WB6BYU]

The bandwidth-enhancing effect of the coax stubs (which provide a compensating reactance
across the feedpoint as the frequency changes) is greatest for lower impedance coax.
You might see if you can find any references to the "Snyder Dipole", which was patented some
years ago (1980's?) and used 25 ohm coax for wider operating bandwidth.  You can accomplish
the same thing by using two parallel stubs on each side, but that makes for a heavier antenna.


Testing antennas well isn't an easy job, especially when using signals that arrive via ionospheric
paths.  Most HF rigs don't have adequate S-meter calibration or resolution for that to be very
useful.  Unless the feedline is very carefully decoupled, it can skew the results.

The best method I've come up with so far for comparing antennas on ionospheric paths is to
access the AGC voltage that drive the S-meter, use an electronic switch to flip back and forth
between the two antennas, then run the S-meter voltage through a synchronous detector
such that the output goes positive when signals are stronger from one antenna and negative
the other way.  By putting variable attenutors in the antenna leads you may be able to
calibrate the meter deflection in dB, but more likely you would adjust one attenuator until
the signals are equal, and read the difference in the attenuators.  (This also allows you to
calibrate out differences in coax loss.)  Then swap the two antennas around for location
and feedline and try again.

If you can put out a steady signal source about 10 wavelengths away and hang the
antennas under test between the same two supports this may give fairly repeatable readings.

On VHF I modified one of my 2m FM rigs to tap off the S-meter reading, which gives much
better range and resolution than the bargraph meter itself.  With a digital meter on this lead
you can read fairly small differences in signal strength - the slope was roughly 0.1V/dB.
Again you would need to calibrate the voltage vs. signal strength, and it may not be linear,
but it gives better precision when switching between antennas.

[KD6RF]

.
I remember "discovering" the parallel stub bandwidth increasing trick some time ago - maybe early 1980's?

A few things I remember -
*  Can use lower impedance coax (or multiple coaxes in parallel), for faster Z change with frequency (as BYU mentioned above)
*  Can use longer coaxes - odd multiples of shorted quarter wave, or multiples of half wave, for faster Z change with frequency
*  Can put the coax stub(s) on the ground (where they belong!) at electrical half wavelengths away from the feedpoint, rather than have bulky heavy stuff waving around in the air sagging and breaking my antennas
        - and most importantly -
* The loss in the system outweighs the minor and theoretically limited broadbanding benefit!!!

The latter bacame very obvious since I also tried this "trick" at 2 meters (where you end up with an antenna that is a little broader band, but a coupla dB down in performance!)....
.
.

[KA0HCP]

Two reasons why a DB may appear quieter than another dipole
1. The known 3dB loss inherent in the design
2. The coax jacket reduces static buildup from precipitation, dust, wind etc. compared to a bare wire antenna.

[N8CMQ]

I did a direct comparison of tower mounted antennas a long time ago.
I had a horizontal dipole, a vertical dipole and a ground plane antenna
that I could switch from one to the other, and change the height of them.

The project took many months, but it was educational, and it proved the
theory presented in the books was spot on. I am glad I did the work, and
earned some experience!

Keep up the experimentation, your knowledge and experience will benefit!

[KB1GMX]

I played with a bazooka at 1M (300mhz) compared to a dipole and a 1.25L dipole (DEZ)
and the DEZ beat all, the dipole was #2 and the Bazooka was down 2db from the dipole.

Why at 1M, I can test there using modest heights and distances with network analyzer
(E8357A). 

The bazooka was design for bandwidth over gain.  Its first application was VHF RADAR
during WW2.  It offered bandwidth and they could make it mechanically stand up to 
winds normally found on the nose of small and fast aircraft.

If you want wider bandwidth, its value is at the expense of gain.  Sometimes that's a
valuable tradeoff.

Allison

[KE4LJH]

Try a Double Zepp 1.5 dB gain or
an Extended Double Zepp 3 dB of gain
+ 450 ohm ladder line
+ 4:1 current balun
+ 10:1 external tuner to give the CONGIGATE MATCH for power transfer
= Very efficient radiator with high swr and better recieve sensetivity.

KE4LJH

[KM1H]

Who needs a wide bandwidth attenuator for 40M? Even a basic dipole covers the full band with under 2:1 VSWR.
If its noisy it is likely common mode noise so install a good ferrite common mode choke at the feedpoint, real cheap if you build it with a few Fair-Rite 2643803802 cores, $4.04 ea at Mouser.

Carl

[KB6HRT]

KB6HRT again,
The longer I tested, things changed some I think now its about the same on receive as the dipole cut for 40m voice, the DB is more broad banded than the dipole. Stations I test with claim the DB has higher incoming reading when on it, could be orientation.  SWR on the DB I could get FLAT 1 to 0 my dipole 1.2 SWR. I used NR 14 stranded THHN for the dipole and RG11 for the DB. both stand up well in the AZ, Sun so no problem eather antenna. Am through testing an have taken the DB down, put up a ZS6BKW that uses 300 ohm LL an NR14 THWN stranded wire, it give me 75m with under 3 SWR 40m under 2 SWR  20m under 1.5 SWR 17m under 2.5 SWR  12m under 1.5 SWR and about the same on the lower part of 10m before using a tuner.  The ZS6BKW is close to the 40m dipole   when I use a tuner on receive.  Getting a little HOT in the summer for me to be up on the roof in July, Aug, Sept and Oct for me to be fooling around with my antennas............73s..........kb6hrt

[W1BR]

If you want bandwidth, consider a fan antenna. It will work far better than antennas that have been analyzed and discredited in the past.

Pete

[K7KBN]

KB6HRT again,
The longer I tested, things changed some I think now its about the same on receive as the dipole cut for 40m voice, the DB is more broad banded than the dipole. Stations I test with claim the DB has higher incoming reading when on it, could be orientation.  SWR on the DB I could get FLAT 1 to 0 my dipole 1.2 SWR. I used NR 14 stranded THHN for the dipole and RG11 for the DB. both stand up well in the AZ, Sun so no problem eather antenna. Am through testing an have taken the DB down, put up a ZS6BKW that uses 300 ohm LL an NR14 THWN stranded wire, it give me 75m with under 3 SWR 40m under 2 SWR  20m under 1.5 SWR 17m under 2.5 SWR  12m under 1.5 SWR and about the same on the lower part of 10m before using a tuner.  The ZS6BKW is close to the 40m dipole   when I use a tuner on receive.  Getting a little HOT in the summer for me to be up on the roof in July, Aug, Sept and Oct for me to be fooling around with my antennas............73s..........kb6hrt

No such thing as "1:0" for a ratio.  "Flat" would be 1:1.