AstroPlane Antenna V-101 is designed for 20 feet support mast, not more.
Their capacitances top hat should not be modified. different height gives different results.
For that reason, is no longer manufactured more.
Sirio TOP-ONE is an 1/4 ground plane antenna with top hat.
This is very different to ASTROPLANE AV-101..
"The Astroplane (AV-101) antenna.
Background.
The Astroplane antenna is a product of 1960s America. Citizen's Band radio was a 23 channel, AM only system and required a license to operate.
FCC restrictions limited the antenna height to 20 feet above the property, and most CB antennas would have been basic 1/2 or 5/8 wave monopole and base loaded types.
The Astroplane was designed to offer an improved radiation pattern, giving greater distance, while still allowing the antenna to be mounted on the roof without exceeding the height limit.
Astroplane
Design.
The antenna is designed to radiate maximum signal from the top section, sending the signal over roof tops to avoid the loss of signal through buildings.
Although the design is intended to have a 1/4 wave top section, this would make the antenna a total of 16 feet. As the antenna should have at least 8 feet of mast below it, the total when mounted would be more than the 20 feet maximum.
The answer was to use a shorter top section of around 1/8 wave length, and top load it to the 1/4 wavelength with a capacity hat (the top radials). This combination lowers the radiation angle, but also decreases the bandwidth.
For wider bandwidth use, this top section can be changed for a straight 1/4 wavelength section.
Quick Reference.
Creators:
Manufacturer:
Louis J. Martino,
Herbert R Blaese.
Avanti Communications
Specifications.
Claimed gain:
Impedance:
SWR:
Bandwidth:
4dBi.
50 Ohms.
Pretuned, below 1.4:1
27 - 29.7MHz.
Measurements.
Please note that component measurements are complete lengths. Once parts are slotted together, the electrical length may be different.
Full length:
Top section length:
Top Radials:
Bottom half length:
Loop Diameter:
Fibreglass rod length:
Mounting pole length:
12 Feet.
4 Feet.
4 of @ 24 Inches
8 Feet.
30.5 Inches.
13 Inches.
> 12 Feet."
