Re: LF: AW: RE: RE: Static protection when using a soundcard as an Rx

[M0FMT <m0fmt@yahoo.co.uk>]

Hi LF

 

I agree fully with Eddie's and Stefan's description in the use of protection diodes. Back to back is a loose term and I tend to use it. However I try to accompany my comments with a circuit diagram to illustrate the point (not so easy on Blacksheep).

 

Could I also add that static or local lightning strike may not necessarily be the worst enemy  of this type of sound card use, because you normally know they are about and disconnect. If you are like me and have various antennas up along side or near to the LF Marconi very strong field strengths (voltages) can be induced into the LW when operating a TX on another bands

 

OK OK I am expecting the usual perfect ops to say I should not have many antennas up at the same time, one degrades the other etc etc... but it is a fact of life so it is worth remembering this issue in protecting your sound card input. I have been thinking of screened hi Q traps right against the SC input. 

73 es GL petefmt

I support www.NotSpotTelecom.Com your community Telco / ISP.

--- On Mon, 14/6/10, Stefan Schäfer <schaefer@hst.tu-darmstadt.de> wrote:

From: Stefan Schäfer <schaefer@hst.tu-darmstadt.de>
Subject: LF: AW: RE: RE: Static protection when using a soundcard as an Rx
To: rsgb_lf_group@blacksheep.org
Date: Monday, 14 June, 2010, 11:20

Hi Eddie,

"Antiparallel" is the description i normally use and i most often heard for such arrangements. :-)

73, Stefan

________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von g3zjo
Gesendet: Mo 14.06.2010 10:33
An: rsgb_lf_group@blacksheep.org
Betreff: LF: RE: RE: Static protection when using a soundcard as an Rx



Hi All



I think I will add a 600ohm 1:1 transformer to my sound card LF set up in addition to the diodes I have at present.



Incidentally it has suddenly struck me what a loose term 'back to back' diodes is. It could be confusing for an enquirer. What is being referred to here is 2 diodes in parallel across the input, one of them one connected one way round and one the other.

Back to back diodes is also a term for two diodes in series connected + to + or - to -, putting the open ends of this combination across the input would do nothing to protect the circuit. Joining the open ends and placing that across the input would not be right either.





Eddie G3ZJO



-----Original Message-----
From: Stefan Schäfer [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Stefan Schäfer
Sent: 13 June 2010 23:54
To: rsgb_lf_group@blacksheep.org
Subject: AW: RE: Static protection when using a soundcard as an Rx



Hi Brian and also welcome :-)



I would combinate back to back diodes with a isolating transformer for audio. A combination of the hints you heared before ;-) The transformer prevents galvanic coupling (could become a problem even if your wire is grounded for high voltages by the diodes) and the diodes on the soundcard side are an additional safety factor that reduces voltage spikes. But the diodes start to conduct already at some 1/10 volts (depending on the temperature) so you may use 2 in series each...



73 es gl becoming QRV!!



Stefan/DK7FC



________________________________

Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von James Cowburn
Gesendet: So 13.06.2010 20:09
An: rsgb_lf_group@blacksheep.org
Betreff: LF: RE: Static protection when using a soundcard as an Rx

Hi Brian



Welcome to the reflector.   Back to back diodes are good option to limit surges and spikes, but others are more qualified than me to advise









With best regards





Jim





Dr. James Cowburn  G7NKS

E james.cowburn@virgin.net



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________________________________

From: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Brian Reay
Sent: 13 June 2010 17:38
To: rsgb_lf_group@blacksheep.org
Subject: LF: Static protection when using a soundcard as an Rx



Hi All,



My first post to the reflector.



I plan to try using a sound card and a "long wire" (well as long as I can fit into the garden) antenna and later a kit lofted antenna but I'm concerned re static.





Normally I'd add a "dc short" with an inductor but at 10kHz than is a big inductor. A resistor is another options.



Does anyone have any other suggestions, please.



73

Brian