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THE AM BULLETIN BOARD => Technical Forum => Topic started by: NC2W on January 09, 2023, 08:50:44 PM

Title: "Colinear Array" for 20m
Post by: NC2W on January 09, 2023, 08:50:44 PM
I am contemplating a 20m 'colinear array'.... (appears as a single dipole, with shorted quarter wave stubs at each end, to which another half wave dipole is attached at each end).  Modelling this on MMANA, it seems to have a 300 Ohm feedpoint impedance (270 +/- j2).  This was with it at 32ft above the ground.  It appears to have a narrow (32 degrees) half power beam width, 90 degrees to the line of the antenna.

My questions:

1.  A 6:1 balun would seem to present a 'good match' (45 Ohms) to a 50 ohm feedline.  I don't find many 6:1 baluns around (some are voltage baluns, and others are 'current baluns').  Are there better ways to match a 270Ohm impedance to 50Ohms, outdoors? (better means as simple, weather resistant, for a single frequency).

2.  Has anyone built and operated such an antenna? (I can find 2m examples of the same)  - Was it as narrow as simulation software makes it out to be?

3.  Has someone published this design as an 'Antenna Article' before?  Could I look up the work someone else did, and duplicate it, with success?

Thanks in advance
Eric - NC2W

Title: Re: "Colinear Array" for 20m
Post by: K9MB on January 20, 2023, 04:20:04 PM
In my “impoverished” youth, I experimented with an extended double zepp array for 20 meters.

Two 5/8 wave dipoles are fed at the center with OWL that is 1/4 or 3/4 wave long.
The feedline is shorted and resonated with a grid dip oscillator and then a 1/2 wave coaxial balun tied to a 50 or 75 ohm coax cable is tapped up from the shorted stub to give 1:1 match at transmitter.

I added two 35 ft wires spaced 17 feet apart with rope about 14-16 feet behind the extended double zepp and a pair of 31 ft wires spaced similarly with rope about 14 feet in front of the extended zepp.
It had a very sharp E plane lobe but since I used it to talk to my father-in law in FL, it dod not matter. Stations from Venezuelaand Columbia broke in and said I was 20 over with 250 watts imto that antenna. I was 10dB stronger than a giy mearby who. Used a SB200 and. Tribander. Covered whole 20 meter band too.
Very simple and efficient…73. Mike
AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands