[amsat-bb] Re: Avoiding statics on helix antennas

[i8cvs]

Hi Joe WB9SBD

The ARRL Handbook explain that you must consider the velocity factor.To put a shorted quarter-wave coax line at the converter input as a short for the statics is easer than to find out from where the statis came from ! 

73" de 

i8CVS Domenico
  ----- Original Message ----- 
  From: Joe 
  To: i8cvs 
  Cc: Lars Petersen ; AMSAT-BB 
  Sent: Wednesday, August 05, 2009 5:52 PM
  Subject: Re: [amsat-bb] Re: Avoiding statics on helix antennas


  don't forget the velocity factor too!

  My first thought was to try to find out where the static is coming from in the firstplace and fix that. Why put a band-aid on a cut when you prevent the cut in the first place?
  Joe WB9SBD

  i8cvs wrote:

Hi Lars, OZ1BXM

The shorted quarter-wave coax line suggested in the ARRL Handbook 2008 and
2009 pages 23.20-21 will work great because it is a short circuit for the
static electricity and a theoretically infinite impedance at the resonant
frequency so that for the RF input signal it is completely ignored by the
input stage of a converter or preamplifier.

Remember that a quarter-wave transmission line when shorted at one end
shows an infinite impedance in theory at the open end as you can see using
the Smith Chart.

If you enlarge a shorted quarter-wave by any even or odd number of  1/2
wavelenght of coax line thing do not changes because a 1/2 wavelenght of
transmission line represents a full turn of the Smith Chart.

Do it as suggested by the Handbook !

73" de

i8CVS Domenico

----- Original Message -----
From: "Lars Petersen" <lars.petersen at pobox.com>
To: <AMSAT-BB at amsat.org>
Sent: Tuesday, August 04, 2009 6:01 PM
Subject: [amsat-bb] Avoiding statics on helix antennas


  
Hello AMSAT list,

I have a problem caused by static electricity building up on my two helix
antennas (23 cm and 13 cm). Two converters have already been zapped, so I
have to do something about it.

What measure would you recommend to avaoid statics building up on helix
antennas?

Does anyone have experience using the shorted quarter-wave-stub mentioned
    
in
  
"The ARRL Handbook 2008" pages 23.20-21?

Vy 73, Lars Petersen, OZ1BXM,
AMSAT-Member 36222,
oz1bxm at pobox.com
www.oz1bxm.dk

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