[hpsdr] Protection Devices - Was: Intelligent or dumb Alex, food for thought...

[Henry Vredegoor]

Hi All, Tommy,

I hope you saw that this was no real post to the subject!
I was answering a fun post of Pieter with a fun answer.

As to the TVS's, it seems that they are objectionable in this application,
as any diode solution in the radio front end.

Although they will do their work and will protect, they also could cause
inter modulation products in normal receive mode.
This because of the hard clipping that occurs when they start to conduct (at
0,6 to 0,7 Volts, in case of the two anti parallel mounted diodes)
There are solutions to change this hard clipping to soft clipping by biasing
them with a resistor to the supply lines but there would still be the chance
of some IM. (and maybe extra noise from having a (small) current running
trough the diode?)

However, the consensus seems to be that the standard, well proven solution
with a standard neon gas filled bulb (limits static voltages to 50 - 70
volts in case of a standard 110 Volt type), a parallel resistor (abt. 100K)
to have a lower impedance to ground (limiting static charge build up) and
the right operating voltages of the antenna input filter components (< 70
Volts) seems still to be a good solution.

73's,
Henry.



> -----Original Message-----
> From: hpsdr-bounces at hpsdr.org 
> [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of Hollingsworth, Tommy
> Sent: woensdag 7 maart 2007 15:29
> To: hpsdr at hpsdr.org
> Subject: Re: [hpsdr] Intelligent or dumb Alex, food for thought...
> 
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Henry:
> I have a surge tester that will go to 25 KV.  I think a one to one
> comparison test of the alternatives would be quite easy!  All 
> approaches
> would need to be installed on a standard (or the same) test 
> fixture, then I
> could test in 1 KV increments until the parts blow or the limit of the
> tester is reached.  This way I can do direct comparisons 
> without damaging a
> radio.  
> 
> I personally like the TVS diodes from Semtech.  The threshold 
> voltage can be
> picked at whatever you want.  The latest parts have 
> capacitance values as
> low as 0.5 pF.   I really do not know what voltage threshold 
> would be most
> appropriate, but if someone else would be willing to test 
> them in their
> radio for distortion, I would be happy to obtain any desired 
> Semtech parts
> and do comparative testing with the surge tester to any desired
> configurations.  I am really curious about how the different 
> approaches will
> stand up to calibrated abuse.
> 
> Tommy Hollingsworth currently KE5LFR 
>  
> 
> -----Original Message-----
> From: hpsdr-bounces at hpsdr.org 
> [mailto:hpsdr-bounces at hpsdr.org] On Behalf Of
> Henry Vredegoor
> Sent: Wednesday, March 07, 2007 1:06 AM
> To: hpsdr at hpsdr.org
> Subject: Re: [hpsdr] Intelligent or dumb Alex, food for thought...
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> Hi all, Pieter,
> 
> You must be coming from the future.....
> 
> No problem with that kind of power, we will use a lightning 
> strike each time
> we want to adjust the frequency.
> 
> 73's
> Henry.
> 
> > 
> > You must be taking about a reluctance tuned variable flux capacitor 
> > filter.
> > Those are typically tuned to 1.21 GHz and require way to much power 
> > (1.21 GW).
> > 
> > :)
> 
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