[Elecraft] Remote Antenna Switches and K2 Questions

[Dauer, Edward]

Thanks for the note, Peter.  I haven’t opened the relay box, not wanting 
to break whatever weather seal it still has (besides,  it’s snowing and 
blowing out there); but I don’t know why a schematic would leave out 
anything that’s actually in the equipment.

I’ve had a half-dozen off-list replies to my original post, almost all of 
them noting the three parallel caps that pass the RF input and 
theoretically isolate it from the relay voltages.  If any of them failed, 
there could be DC showing up at the RF input.  Don Wilhelm pointed out 
that because the LPF in the K2 is grounded on one side the presence of DC 
itself wouldn’t be a problem, but that rapid changes in any voltage 
getting into the RF input side could be. (Do I have that right, Don?)  The 
curious thing, though, is that I have two Ameritron RCS-4s, and these 
voltage anomalies appear in both of them in almost identical ways.  Maybe 
a design flaw rather than a component failure?  In any case, something 
caused multiple failures when the K2 was here, but not when the K2 was 
anywhere else; and having the RCS-4 in the line here is the last such 
difference I could think of that hasn’t already been ruled out.  So maybe 
it has been a K2 component problem, but maybe not - three nearly identical 
failures make that seem less probable than only one would, but snot 
unlikely.

What I’ve measured with the DMM are short bursts - and, in fact, at one 
point I saw a reading of over 18 volts as your note suggests might be 
possible.  I am bringing one of the units back to the city with me Monday, 
where my oscilloscope is, so that I can get a better picture of what these 
transients look like.

For now I am just being wary of a system that inserts the relay energizing 
voltages into the coax.  The disadvantage of the alternative, meaning a 
separate low-voltage cable from the control box to the relays, is that 
it’s another cable.  For reasons of good domestic relations the coax from 
the house to the common antenna feed line site is buried.  Any other 
cables running that way would have to be as well.  From the looks of 
things today it may be June before the ground at this altitude (8,600 
feet) thaws enough to allow for even shallow trenching.

My thanks to everyone who replied with observations and suggestions.  This 
list is a never-fails resource . . . 

Ted, KN1CBR








On 3/26/16, 4:42 PM, "Peter Eijlander (PA0PJE)" <pa0pje at xs4all.nl> wrote:

>Hi Ted,
>
>I just looked at the schematic, downloaded from the Ameritron site, and 
>wondered whether or not there are any protection diodes across the 3 
>relay coils in the remote box. They do not show on the drawing.
>
>I can imagine these spikes could be much bigger than the +5 and -5 volts 
>you quote.
>
>73,
>Peter - PA0PJE