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Author Topic: Aerials outside  (Read 3319 times)

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3 greens

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Aerials outside
« 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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klm

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Re: Aerials outside
« Reply #1 on: January 06, 2010, 08:12:42 am »
Like this




to my experience works a vertical antenna better as dipool on this freq.
because the line of side thing
« Last Edit: January 06, 2010, 08:36:36 am by klm »

Jeremy

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  • Jeremy
Re: Aerials outside
« Reply #2 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.
G4DOQ
QRZ.com

Dean

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Re: Aerials outside
« Reply #3 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.

Jeremy

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  • Jeremy
Re: Aerials outside
« Reply #4 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.
G4DOQ
QRZ.com

3 greens

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Re: Aerials outside
« Reply #5 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)

3 greens

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Re: Aerials outside
« Reply #6 on: January 09, 2010, 03:55:24 pm »




My outside array. And hope to build this aerial, may fit when the weather turns for the better
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« Last Edit: January 09, 2010, 03:59:14 pm by 3 greens »