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Re: L-Band Antenna



Joel,

You are right on.  I like to make the calculations a little low in
frequency.  If you note that the bandwidth is about 1.8:1, then it really
is better to let the bottom end on the freq range drop down a little.
Your design should give about 16 to 17 db gain.  BTW the helix is very
forgiving of small errors in calculations and construction.

Now build it and "be ready". It shouldn't be much longer before you get a
chance to try it.

73...Jim...W5VZF

Dr. Jim Akers
Dept. of Electrical 
and Computer Engineering
Miss. State Univ. 


On Thu, 23 Nov 2000, Joel B. Black wrote:

> I thought it would be interesting, with all the talk of S-Band, to do the
> calculations for an L-band helix for AO-40.  I did this in an Excel
> spreadsheet so some of the formatting may look wrong.  Also, I couldn't get
> Excel to calculate tangent, cosine, and square root correctly so those were
> done manually.  Some of you "gurus"  can confirm or discount my
> calculations.  I got them from the _The_Radio_Amateur's_Satellite_Handbook_
> 1st. edition, page 10-11:
> 
> Free space wavelength (inches) = 11,800/f (MHz) 9.30inches (23.62 cm)
> Diameter  = C/p 2.96inches (7.52 cm)
> Spacing between turns  = C(tan a) 2.06inches (5.23 cm)
> Distance between reflector
>      and start of first turn  = S/2 1.03inches (2.62 cm)
> Reflector side (minimum)  0.6l 5.58inches (14.17 cm)
> Wire length per turn  = C/cos a 9.53inches (24.21 cm)
> Total wire length  = nL + 1/2  144.75inches (367.67 cm)
> 
> Circumference: C =  1.00
> Pitch angle: a =  12.5
> Turns: n =  15
> Antenna center frequency: 1269.250
> 
> 73,
> Joel, K2SAT
> 
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