[Elecraft] [Elecraft_K3] Re: P3 adding rf protection diodes question

[Alan Bloom]

BNC connectors are designed in such a way that the shield always 
connects before the center conductor when you plug it in.  The only way 
to get a static discharge into a female BNC is to somehow touch the 
center conductor (with your finger or whatever) without touching the 
shell.  You would need to use a tool to do that unless you have REALLY 
skinny fingers.  :=)

Alan N1AL


On 05/20/2014 11:31 AM, Fred Townsend fptownsend at earthlink.net 
[Elecraft_K3] wrote:
>
>
> Alan, thank you for the good information on how to setup the P3 as a
> "poor ham's spectrum analyzer". However I must disagree with your first
> statement. Diodes for ESD protection are needed in normal use with the
> K3. When ESD occures it is frequently at connector interfaces because
> the two mating bodies may be at different potentials. Good design
> practice for ESD is to protect connector interfaces if the user will be
> mateing and un-mateing. This is clearly the case with the K3/P3
> combination. Diodes are soo cheap when applied in the SMD process it
> seems like a no brainer to include ESD protection. Defeat Murphies law.
>
> 73
>
> Fred, AE6QL
>
>
>     -----Original Message-----
>     From: "Alan Bloom alan at elecraft.com [Elecraft_K3]"
>     Sent: May 20, 2014 10:42 AM
>     To: elecraft at mailman.qth.net, Elecraft_K3 at yahoogroups.com
>     Subject: [Elecraft_K3] Re: [Elecraft] P3 adding rf protection diodes
>     question
>
>     The diodes are not needed in the normal situation where the P3 is
>     connected to the K3 IF output.
>
>     You can use the P3 as a kind of "poor ham's spectrum analyzer" by going
>     into the menu and setting "Xcvr Sel" to the last item in the list,
>     labeled "0 Hz". Now the frequency displayed is the actual RF frequency
>     of the IF input, not the K3 frequency. The "XCVR" RS-232 connector
>     should be disconnected from the K3 in this case. Tune the frequency
>     with the CENTER control. (Make sure the "CenterEn" menu item is "ON".)
>
>     If you do that you should add the back-to-back diodes in parallel with
>     the input BNC connector. Standard 1N4148 or similar switching diodes
>     are
>     fine. If you don't want to modify the P3 you can do what I did: Add
>     the back-to-back diodes to a male BNC connector and connect that to a
>     BNC "T" plugged into the P3 IF IN.
>
>     There may be some slight degradation of dynamic range. The third-order
>     intercept of the P3'! s preamplifier is about +9 dBm (0.6 Vrms). If
>     you're worried about it you can use two diodes in series in each leg (4
>     diodes total) to reduce the distortion contribution from the diodes.
>
>     Alan N1AL
>
>     On 05/19/2014 06:38 AM, Sam Morgan wrote:
>      > It was mentioned to put a couple of diodes across the P3's input to
>      > protect it. Do the diodes need to be 1n34a's or would 1n4148's be
>     ok for
>      > that application?
>      >
>      > I had tried repeatedly to ask Don W3FPR this question off list via
>      > direct email, but I guess all my efforts have ended up in his spam
>      > folder?? :-(
>
>
>
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> Posted by: Fred Townsend <fptownsend at earthlink.net>
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