[Elecraft] K3: Added protection for RS-232 port

[Don Wilhelm]

Pete,

Since you are concerned, I would suggest adding some MOVs between the 
RS-232 port pins 2, 3, 4, and 7 and ground.
MOVs rated at 25 volts should be sufficient.

I have read a few (but very few) reports of lightning surges taking out 
the RS-232 port, but in all cases that I have known about the computer 
was also damaged, so it is difficult for me to say that the K3 RS-232 
port is any more "fragile" than any other component.

There may be valid concerns if one lives in a high lightning incident 
area and do not have extensive lightning protection installation at your 
station, every piece of equipment in the hamshack may be at risk, but 
there are ways to minimize that risk.

I would rather suggest that you do some work on lightning protection.  
Do a search on the ARRL website for "lightning protection" and look 
especially at the 3 part series authored by Ron Block.  That is good 
information about how to make your station (and your family) more safe.
For good protection, the installation of several grounding radials 
around the tower (or mast) with driven ground rods at periodic intervals 
and a perimeter wire around the house, all tied into the utility 
entrance ground will go a long way toward affording some lightning 
protection.   Those ground radials help to dissipate the energy in a 
lightning surge over a large area of the earth - the wire should be as 
large as you can get - #6 is the smallest I would consider.

In addition, bringing all lines into the station (including AC mains 
power, telco, LAN as well as antennas, rotor cables and control lines) 
through a single point grounding panel which has protective devices 
installed on each and every line, and connect every chassis in the shack 
area to that single point entry panel.

A station ground system of the type I have described is much better 
insurance for containing surges than doing something to beef up 
protection on any particular device.  It is not easy, nor is such 
protection inexpensive, but I deem it important.

73,
Don W3FPR
 

Pete Smith wrote:
> Don, I have read several reports on this list of RS-232 failures 
> (probably implicating U1 on the KIO3A) apparently due to induced 
> voltage.  My comment was based more on my having used radios with serial 
> ports for some 15 years and never had any problem with the ports, 
> despite leaving serial cables connected all the time.  Elecraft advised 
> me always to disconnect any cable from the RS-232 port on my K3 when not 
> in use, from which I inferred fragility.
>
> Anyway, the point is that I'm ready to add some protection, if I can 
> figure out how to do it.
>
> 73, Pete N4ZR
>   
>