[hpsdr] ALEX - Input protection

[Graham Haddock]

Chris:

You are absolutely correct about the lightning.

This is just a transient suppressor, only intended to deal
with lower level spikes and ESD.  The real lightning protection
MUST take place up stream from any transmitter or
receiver. 

For reference and reading on lightning protection,
I recommend the papers on the PolyPhaser site.

http://www.polyphaser.com/

http://www.polyphaser.com/technical_notes.aspx

See:

TD1005: Lightning protection inside the equipment is not always a good 
idea.. 
<http://www.polyphaser.com/NR/rdonlyres/C1565001-F81A-4AC2-A98F-E88B8037F988/171/TD10095.pdf>

TD1016: Ham radio station protection. 
<http://www.polyphaser.com/NR/rdonlyres/C1565001-F81A-4AC2-A98F-E88B8037F988/182/TD1016.pdf>

--- Graham


Chris Stake wrote:
> Hi Graham,
>
> Many thanks for explaining about Reply All.
>
> IMHO two effects could damage your radio via the aerial:
>
> a/ Static discharge:
> can be bled to earth via a high-value resistor. No danger.
>
> b/ Lightning strike:
>
> provide an lower IMPEDANCE path to ground than thru the front end of the
> radio. The currents can be Kilo Amps. Nothing you do inside the case will
> protect the electronics.
>
> Maybe flashover devices and fusible links in the antenna, 
>
> Regards Chris
>
>
>
> Regards
>
> Chris
>
>
>
>
> -----Original Message-----
> From: Graham Haddock [mailto:KE9H at austin.rr.com] 
> Sent: 08 August 2007 00:40
> To: Chris Stake
> Subject: Re: [hpsdr] ALEX - Input protection
>
> Hi Chris:
>
> On this group, if you just hit reply, it goes to the original sender.
> If you hit Reply All, it will also pick up the entire group.
> Backwards from the way I think it should work, but I am not running things.
>
> All of these devices are spec'ed with a "standard" pulse, with 8 us rise
> time and 20 us fall time, which I think puts it in the realm of both 
> lightning and
> ESD waveforms.
>
> --- Graham
>
> ==
>
> Chris Stake wrote:
>   
>> Hi Graham,
>>
>> Sorry to send this to you direct, I can't get the hang of this group or
>> where to post correctly.
>>
>> I looked at this sort of device long ago and buried in the specs was a
>> problem:
>> Some are slow, transient forward voltage is high. Little genuine static or
>> lightening protection for logic level inputs.
>>
>> The low - C ones seemed to avalanche slower. 
>>
>> Maybe they're better now.
>>
>> We decided to use a low cost (sacrificial) input device instead.
>>
>> Hope this helps
>>
>> Chris Stake
>>
>>     



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