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ACRO E-mail Archive Thread: [Acro] Re: Help with some radio education

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ACRO E-mail Archive Thread: [Acro] Re: Help with some radio education



                


Thread: [Acro] Re: Help with some radio education

Message: [Acro] Re: Help with some radio education

Follow-Up To: ACRO Email list (for List Members only)

From: "Andrew Boyd" <aboyd at igs.net>

Date: Tue, 20 Aug 2002 04:34:58 UTC


Message:

  From: "John Harlan" <jmharlan at ev1.net>

> use your original hand held antenna .... Maybe the
> range isn't as good as with a "real" antenna, but it works ok.

A "real" VHF comm antenna shouldn't cost very much
or be very hard to build from scratch.

From first principles, velocity equals frequency times 
wavelength, or:

v = f x lambda
lambda = v / f

v = 3 x 10^^8 meters/sec (speed of light), and

f = 120 Mhz = 120 x 10^^6 = 1.2 x 10^8

therefore lambda = 3 / 1.2 = 2.5 meters 

From the dim recesses of my memory, a 1/4 wavelength
"marconi" antenna should do the job nicely.  Google
turned this up, and explains why we need a ground
plane:

http://www.tpub.com/inch/28.htm

So, 2.5m / 4 = 62.5 cm

convert to inches for the non-metric crowd:

62.5 / 2.54 = 24.6 inches

So, all we really need is a stinkin' piece of wire
about 25 inches long, mounted perpendicularly (and
insulated from) a ground plane, for a pretty good
120Mhz VHF comm antenna.

P.S.  Hey Chris, say "hi" to Craig at DOT enforcement 
for me when you forward this to him from the list as 
per usual, ok?

--
aboyd at igs.net   ATP  http://www.webhost-canada.com/~boyd/team.htm



                


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