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[AMPS] glitch resistors

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Subject: [AMPS] glitch resistors
From: Ian White, G3SEK" < (Ian White, G3SEK)
Date: Sat, 8 Sep 2001 19:50:38 +0100
OZ5IQ wrote:
>HI Tom, W8JI and the group
>TNX for your answer to my comment. Always gd to have tech. discussions. HI    
>Just think of how we would have been IF we always have been listening to our 
>ones. but to your comment
>>> I Always put those current limiting devices at the LOW voltage
>>> potential.
>>That's not a solution I'm afraid.
>Well you shold NOT be - and of the following reasons:
>>When you have an arc, the resistor MUST be able to handle the full 
>>supply voltage across the terminals of the resistor no matter where 
>>it is located in the path.
>Thats not correct - why you forget the selfinduction in the trafo !  How do 
>think it behaves for lets say  even  1mS arc ?  Yes, the rise in voltage will 
>NEVER travel through the trafo, why the "pulse" is at that short time  !!    
>may transfer pulses at longer period yes, but not that short - they will "die" 
>relatively short time after entering the trafo.
>>That is why you always need a suitable HV resistor, even if you 
>>place it in the negative rail....which is a terrible place to put it 
>>anyway because it is bypassed by all the stray C in the power 
>>supply and requires the negative rail to lift to supply potential in 
>>order to limit current!
>remember the transfer speed capability of a trafo.
>its another thing when talking ferrite trafoes - you may be right.
>So - yes theres an easy way out !

The initial current pulse comes out of the smoothing capacitor, so the
transformer inductance does nothing to help.

This same discussion happened here some months ago, and I put together a
little web page with schematics. It's still there, at:

73 from Ian G3SEK          Editor, 'The VHF/UHF DX Book'
                          'In Practice' columnist for RadCom (RSGB)

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