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)" <[email protected]> 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 ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to [email protected]
