AirNav Systems Forum

AirNav RadarBox and RadarBox24.com => AirNav RadarBox and RadarBox24.com Discussion => Topic started by: 3 greens on January 05, 2010, 11:58:15 PM

Title: Aerials outside
Post by: 3 greens on January 05, 2010, 11:58:15 PM
Due to the high frequency of the air nav box I would assume that the aerial should be cut to the correct length ?   I am using a discone for V.H.F. and U.HF. I also have a dipole cut to approx   400 x 400 mm.  I use them both for civil and mill comms. Help on this would be welcome. My thought would be approx   200x200 mm in a vertical dipole format
The present  array is situated outside and quite high up...

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Title: Re: Aerials outside
Post by: klm on January 06, 2010, 08:12:42 AM
Like this

(http://www.airnavsystems.com/forum/index.php?action=dlattach;topic=4123.0;attach=5735)
(http://www.airnavsystems.com/forum/index.php?action=dlattach;topic=4123.0;attach=5736)

to my experience works a vertical antenna better as dipool on this freq.
because the line of side thing
Title: Re: Aerials outside
Post by: Jeremy on January 06, 2010, 10:37:49 AM
Antennae must be virtical. An inverted V only has slight virtical properties. Calculate by 300 = Freq x wavelength
6.8 cm each side for a diplole.
For VHF airband 60cmx60cm
fed with 50 ohm coax.
Virtical dipole should work fine.
J.
Title: Re: Aerials outside
Post by: Dean on January 06, 2010, 09:27:04 PM
Can't see any benefit in turning a dipole on its side at 1090 MHz. There are properly designed (commercial & build yourself) verticals available that will give better results. With a vertical at these frequencies it's quite easy to simulate the ground plane using very short radials , in effect that's what the metal plate on the supplied antenna is doing.

Dipoles (H mounted or V) have big nulls in them and little overhead coverage.

Bear in mind the signal transmitted will be vertically polarised so you may suffer phasing losses if trying to receive it on a horizontal.
Title: Re: Aerials outside
Post by: Jeremy on January 06, 2010, 09:53:42 PM
That was my point! What is it, 30Db loss between horizontal and vertical? Any aircraft overhead will still be heard even if it is on the null!
J.
Title: Re: Aerials outside
Post by: 3 greens on January 08, 2010, 08:58:48 PM
Many thanks for the input.....I am sure that Vertical for the inner, and radials for the outer. How-ever due to the poor weather I think climbing around erecting a new aerial outside is to say at the least a mad idear.   (12" snow and - 9)
Title: Re: Aerials outside
Post by: 3 greens on January 09, 2010, 03:55:24 PM
(http://)(http://i160.photobucket.com/albums/t171/taylorraymond/arieal.jpg)

(http://)(http://i160.photobucket.com/albums/t171/taylorraymond/scan0002-4.jpg)

My outside array. And hope to build this aerial, may fit when the weather turns for the better
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