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Fw: Re: 2.4 Ghz Helix



Sorry lads I forgot to send this to the BB

Joe  K0VTY
=============================
--------- Forwarded message ----------
From: Joseph Murray <K0VTY@juno.com>
To: w4mvb@juno.com
Date: Wed, 23 May 2001 22:38:11 CDT
Subject: Re: [amsat-bb] 2.4 Ghz Helix

Hi Jesse


>From what I am reading,  multiple helix arrays have mutual impedance of
the adjacent helices.
Both resistive an reactive.    I have a graph the shows the resistive and
reactive components of the mutual impedance of a pair of same handed  8
turn monofilar axial mode helical antennas as a function of seperation
distance in wavelengths  Where C=1 and pitch =12 ) 

The conclusion is " at spacings of a wave length or more , as is typical
in helix arrays ,  the mutual impedance is only a few percent or less of
the helix self impedance  ( 140 ohms resistive ) .   Thus , in designing
the feed connections for a helix array the effect of the mutual impedance
can often be neglected  without significant consequences ".     

This article shows spacings of 1.5 WL for a four helix array.    The
direction of the article is one where the decision needs to be made on
whether to have one long helix or to have more shorter helices.  
The article stays with the " I need 24 dB gain , how do I get that gain ?
  1 helix or four in an array.  "
The 24 db appears to be a upper expectancy for a helix one way or the
other .
In this article there is no mention of how long a helix can be nor how
length effect the seperation when in an array.     It appears the the
matching or VSWR increases as the frequency increases.   No indication
why.
I have to suppose that it is typical of greater numbers of members in the
array make it more difficult.

Have fun

Joe  K0VTY
=============================
On Wed, 23 May 2001 21:05:51 edt Jesse Morris <w4mvb@juno.com> writes:
> Good Evening to All,
> 
> I've run the numbers I found in the the UHF/Microwave 
> Experimemter's
> Manual and they seem to incicate that the optimum stacking distance 
> for
> two 20 turn helicies is about a foot.  Can someone tell me if that 
> is
> close to the correct value?  It seems a little close to me 
> considering
> the boom length is about 2 feet.
> 
> Yea, I know, I should buy a dish but I'm hardheaded!
> 
> 73's de Jess - W4MVB
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> 
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