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Maxgain
Junior Member
Username: Maxgain
Post Number: 19
Registered: 3-2007
| | Posted on Friday, April 13, 2007 - 2:42 pm: | 
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Is the support mast part of the astroplene antenna desighn?
Can it be mounted on a non conductive mast and still work ? |
Maxgain
Junior Member
Username: Maxgain
Post Number: 20
Registered: 3-2007
| | Posted on Friday, April 13, 2007 - 3:43 pm: |
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At the top of the astroplane there is a capacity hat of 4 radials 2feet long each. If the capacity hat was removed could the upper vertical element be lengthened to ( I'm guessing about 8 feet ), would the antenna still work the same? |
Rumblefish
Junior Member
Username: Rumblefish
Post Number: 36
Registered: 12-2002
| | Posted on Saturday, April 14, 2007 - 5:22 am: |
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yes the cte top one can be mounted on a non conductive mast, the coaxial cable must run down the mast and past the bottom hoop of the the antenna. I've experimented with removing the capacitance hat and adding a vertical radiator. I fastened a 4 foot whip to the existing 4 foot section and trimmed it to size. 1.5 swr on channel 20.vs 1.3 with cap hat. Increased static with the the extended radiator on receive... no signal increase noted.the avanti engineers did all the homework on this one. TWO thumbs up for this antenna!!!! steve |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 2484
Registered: 9-2004
| | Posted on Saturday, April 14, 2007 - 10:38 pm: |
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rumblefish is right.
you can use a non conductive mast, as long as the coax is secured to the mast for at least 9 feet below the bottom hoop.
as for the top piece being replaced by a 1/4 wave radiator, yes it can be done, and yes the SWR will still match up.
the problem lies in the take off angle.
avanti's engineers addressed this possibility in the patent sheet.
the way it works is, the vertical radiator is 1/8 wavelengh, and the horizontal radials are a capacity hat with a length of 1/8 wavelength, making the top radiator a 1/4 wave radiator.
if you were to make the vertical part longer, the cap. hat radials would be made shorter and shorter until when you got to about 102" on the vertical, the cap hat would not be needed at all.
the SWR would not change as long as you always ended up with a combo that gives 1/4 wavelength total.
the engineers at avanti experimented with this, and found that the cap hat being where it is gave the lowest take off angle, therefore the best DX grabbing ability.
they state in the sheet that in applications where a high angle of radiation is desired, that the cap hat can be subbed for another 1/8 wavelength of vertical length.
so, while it can be done, avanti already did the testing for us, and gave us the best design for what we use the antenna for.
maxgain, be sure to do a search on the forum for "astroplane", and "top one".
lots of good info and tips on installing this antenna.
best of luck,
matt
anyone wanting a "clean signal", just look to the left and build one of these!!!
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