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@pobox.com www.oz1bxm.dk
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@pobox.com To: AMSAT-BB@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@pobox.com www.oz1bxm.dk
Sent via AMSAT-BB@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
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@pobox.com To: AMSAT-BB@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@pobox.com www.oz1bxm.dk
Sent via AMSAT-BB@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
Sent via AMSAT-BB@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
No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.406 / Virus Database: 270.13.44/2283 - Release Date: 08/05/09 05:57:00
Try a grounded radome to keep rain and air movements off the antenna.
Joe wrote:
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
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@pobox.com To: AMSAT-BB@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@pobox.com www.oz1bxm.dk
_______________________________________________ Sent via AMSAT-BB@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
_______________________________________________ Sent via AMSAT-BB@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
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No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.406 / Virus Database: 270.13.44/2283 - Release Date: 08/05/09 05:57:00
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@pobox.com To: AMSAT-BB@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@pobox.com www.oz1bxm.dk
Sent via AMSAT-BB@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
----- Original Message ----- From: "Lars Petersen" lars.petersen@pobox.com To: AMSAT-BB@amsat.org Sent: Thursday, August 06, 2009 12:56 PM Subject: [amsat-bb] Re: Avoiding statics on helix antennas
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)
Hi Lars, OZ1BXM
A grounded radom is still transparent for the static electricity and obviously for RF as well so that a radome is unusefull to avoid statics.
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)
This one is a good method because the input stage do not see the very high impedance of the shorted quarter-wave coax line so that the original Noise Figure of the downconverter is not degraded while the static voltages are shorted out.
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).
A 47 k resistor or an inductor to ground of your converter implies that you have to open the converter box and modify it.In addition a resistor shoves inductance as well and an inductor do shoves capacitance as well so that at 23 cm or 13 cm they will modify the input mached impedance for the lovest Noise Figure of your downconverter. More over a high pass filter designed for 50 ohm with an inductor to ground has an insertion loss that in dB adds to the actual Noise Figure of your downconverter.
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)
For static protection about 2 cm of wire wound around a former to make about half a turn and then soldered from the pin of the N connector and ground do short out the stastic voltages but it modifies the impedance of the helix antenna so that you have to compensate for it twiking with the usual quarter wave strip of brass soldered to the first quarter turn of the helix until you get again a VSWR very close to 1
73 de OZ1BXM Lars Petersen, Holstebro, Denmark
Best 73" de
i8CVS Domenico
----- Original Message ----- From: "Lars Petersen" lars.petersen@pobox.com To: AMSAT-BB@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@pobox.com www.oz1bxm.dk
Sent via AMSAT-BB@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
Sent via AMSAT-BB@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
participants (4)
-
i8cvs -
Joe -
Lars Petersen -
Nigel Gunn G8IFF/W8IFF