[TowerTalk] Double Bazooka question

[K7GCO@aol.com]

In a message dated 10/31/00 2:23:30 PM Pacific Standard Time, 
mdbrown@iquest.net writes:
<< Is there much advantage in using a Double Bazooka antenna 
 when compared to a conventional dipole for 80 meters ?
 
 Thanks... 
 Mike K9MI
  >>
The "Single Type Collins Bazooka" ss a method of broad banding the dipole 
does a great job along with being a balun for balanced feed.  It's heavy but 
it works.  You can cover both Phone and CW with it.  Collins used to show 
this in their instruction manuals.  For proper balanced of the SWR curve, cut 
antenna for 3750 MHz and prune accordingly if Bazooka is not resonant at 
3.75.  

Another K7GCO technique is to cut antenna for 3.55 MHz, cut .66 VF coax 92' 
long and use a conventional balun.  Actually the Bazooka is the best balun of 
all.  Install a 3 gang BC variable Xc in a box with it in series with the 
center lead.  Use and insulated shaft coming out of the box.  Bend a couple 
rotor plate over to short out to the stator plates when completely meshed.  
Adjust for lowest SWR at about 3.55 or 3.6 MHz as this will give about the 
best over all SWR curve with the variable Xc.  This was one who just couldn't 
understand that. 

The way it works is as you operate above the resonant frequency, the antenna 
becomes inductive reactive which reflects the same reactance at the end of 
the 1/2 wave feedline.  Open wire line of .98 VP will work just as well if it 
is 135.4' long as well as 450 ladder line of .89 VP of 123'.  Connect one of 
the balanced open wire line to the rigs ground and the other lead to the box 
with the series 3 gang BC variable Xc and then to the center lead of the 50 
ohm coax jack.  Shorten this lead the amount of the variable Xc box and lead 
to the rig.  Don't worry about the SWR with just a half wave over say 300 KHz 
frequency change despite what certain people are concerned about.  This is a 
balanced feedline feeding an unbalanced 50 ohm input on the rig.  Don't worry 
about it.  I talked to the RF and it will behave. The variable Xc will cancel 
the inductive reactance leaving only the resistive component which rises only 
about 40% at 4 MHz still proving a good match.  If the dipole is at a height 
where it is say 40-50 ohms at 3.55 MHz, you will have a very good SWR curve 
over the whole band.  It is helpful to use a cage dipole cut at say 3.55 MHz. 
 It the center of the dipole is over about .2 WL high, lower the Rr by 
bending the ends down as an inverted vee to obtain 50 ohms.  Remember with 
this technique the Rr always rises as you operate higher in the band.  K7GCO

--
FAQ on WWW:               http://www.contesting.com/FAQ/towertalk
Submissions:              towertalk@contesting.com
Administrative requests:  towertalk-REQUEST@contesting.com
Problems:                 owner-towertalk@contesting.com