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

[Fred Townsend]

Alan I wish it were so but sadly, fat fingers or no, BNC connectors will typically fail ESD testing unless protected by internal circuitry or external covers. That's because ESD can easily jump a 1/4 inch.
73
Fred, AE6QL


-----Original Message-----
>From: Alan Bloom <n1al at sonic.net>
>Sent: May 20, 2014 2:28 PM
>To: Elecraft_K3 at yahoogroups.com, elecraft at mailman.qth.net
>Subject: Re: [Elecraft] [Elecraft_K3] Re: P3 adding rf protection diodes	question
>
>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?? :-(
>>
>>
>>
>> __._,_.___
>> ------------------------------------------------------------------------
>> Posted by: Fred Townsend <fptownsend at earthlink.net>
>> ------------------------------------------------------------------------
>>
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