[hpsdr] ALEX - Input protection

[Henry Vredegoor]

Hi Graham, All,


Would a (broadband) input transformer help in this respect?

A permanent connection to ground of one side of the 50 Ohm input winding
would discharge the antenna system permanently.
Also as ground loop prevention?
Could be part of some filter in ALEX ? 

IP3 of the device could be a problem.


Just a few thoughts.

73 's,

Henry.



> -----Original Message-----
> From: hpsdr-bounces at lists.hpsdr.org 
> [mailto:hpsdr-bounces at lists.hpsdr.org] On Behalf Of Graham Haddock
> Sent: zondag 5 augustus 2007 17:36
> To: hpsdr at hpsdr.org
> Subject: [hpsdr] ALEX - Input protection
> 
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> All:
> I am looking for ideas for input protection for ALEX.
> 
> Lyle has recommended a gas-discharge tube device, which I will use
> on any port that could be hooked to an antenna to limit large voltage
> surges. (Digikey 495-1475-ND)
> 
> But, I have a concern, that the gas-discharge tube limits in 
> the 70 volt
> range, and the Hittite electronic switches and electronic attenuators
> on Mercury will probably break down at lower voltages, I am
> guessing in the 25 volt range.
> 
> Frank Carcia has recommended using low capacitance diodes
> (1N4148 or similar) biased at around +/- 10 volts, so that they would
> clamp the input at that voltage.
> 
> Does anyone else have any other ideas that they would suggest?
> 
> I am looking for something that would present a fairly low capacitive
> load to the input lines, and clamp at a voltage that must be 
> higher than
> about +/- 2.5 volts, but lower than +/- 12 volts.
> 
> Thanks,
> --- Graham / KE9H
> 
> ==
> 
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