Topband: TX relays

[Tom W8JI]

Hi Mike,

> The contacts are not gold-flashed, that's just the lighting and 
> reflections
> that makes it look that way in the photos. They are a cadmium-free silver
> alloy. Here's the data sheet.

Silver is a poor material for most environments without wetting currents 
because of sulfidation. It is certainly better than cad contacts, but 
ideally contacts should be gold flash for maximum reliability in receive 
applications. Of course TX power will break down the sulfide, and restore 
receiving.

> But, this discussion does not answer Milt's original question, because he
> wants a DPDT relay. :-)
> He said "I am looking for some 12 VDC units that are capable of handling
> full legal limit power to install in a controller for a multi-element
> directive array." Maybe we can get back on track here.

To pick a relay, one usually has to understand the system in some depth. 
Milt has an unusual system in that his system has inactive elements that are 
in an area of intense local field levels connected through odd quarter wave 
feedline. The system has to disable the unused elements without having 
excessive voltages across open contacts.

The impedances at the common point are also nowhere near 50 ohms, and we do 
not know the voltage distribution.

Without knowing open circuit voltage levels and operating voltages and 
currents, I couldn't possibly make a suggestion. What works in my system are 
the DXE smaller relays, but my system is entirely different than Milt's.

> I have a half-dozen sealed 12VDC DPDT relays that I am going to use (among
> other things) to switch the low-Z sections of my remote tuner/band switch.
> They're rated at 8A and have 5 kV insulation (and maybe that's
> conservative) between coil and contacts. I'm pretty confident they will
> handle the legal limit even with a little mismatch. (And these are not for
> any receiving application here.)

The dc or hot switch current rating has little to do with how they work at 
30 MHz, and we have no idea what the operating parameters in Milt's system 
are. I know the requirements are different from my directional antennas, but 
that is all I know.

I need a clutch for my home made car. It has four tires. What clutch will 
work? Give me a part number. Same thing, if you see what I am saying.

73 Tom