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

[Lars Petersen]

Hello list,

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

Several suggestions have been given, both here and as PM. Thank you to you 
all! Here is a summary of the mails received:

Answer 1: Try a grounded radome to keep rain and air movements off the 
antenna. (G8IFF/W8IFF)

Answer 2:  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. 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! (I8CVS)

Answer 3: Can I suggest: a) A 47k resistor across the input of your 
converter. The static will have a very high impedance and I've found 47k 
will remove it without increasing the noise figure of your converter. b) For 
really severe cases: An inductor to ground. An 0805 or smaller device. 
Something that presents a couple of Kohms at the frequency of interest would 
be OK. Or perhaps a high pass filter designed for 50 ohms with an inductor 
to ground. Cut off frequency at 30% lower than 23 or 13cms (G0MRF).

Answer 4: An earlier version of the ARRL handbook has a multi turn helical 
for 23cms with the usual quarter wave strip of brass soldered to the first 
quarter
turn of the helix. For static protection it has about 2cm of wire wound 
around a former to make about half of a turn. This is soldered to the pin of 
the N connector and
grounded. I can send you a picture later today. Done.(G7HIA)

73 de OZ1BXM Lars Petersen, Holstebro, Denmark

  ----- 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
>
> _______________________________________________
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb