With silver-cadmium relay contacts I use on my ladder line switching, I find I have to occasionally transmit a dit to get receive to work again, especially if I haven't been on the radio in hours or days. My mental model is that I have to "blow through" the surface contamination. Would definitely never use the silver-cadmium contacts in a receive-only path. (Even though I have been known to make some Q's while transmitting on my receive antennas, it was purely by accident!)
I picked up a tray of some dinky 24V-coil microwave relays that KM1H and W3LPL recommended from Electronics Goldmine and they work great for receive-only applications. (And have survived the occasional accidental transmit!). Tim N3QE On Mon, May 18, 2015 at 8:49 AM, Tom W8JI <[email protected]> wrote: > DC or low frequency AC is an almost meaningless test, although field life > is a good data point. > > The only valid bench tests for a relay in these applications are RF > heating with high current, and voltage breakdown. Some relays even run > current or voltage through the coil pole center, making a "capacitor" to > the control pins. The relay has to be opened and inspected, or measured for > stray capacitances. > > Almost always the heating is in the contact bar or wire to the contact > bar. Heating there is aggravated by RF current and skin effect, so it must > be tested at radio frequencies. > > Contact materials should be gold overlay and ideally have a small contact > area, otherwise they develop receiving issues more frequently. The larger > and more robust the hot switching, the less reliable the receiving becomes. > > I find relays that can reliably carry 20-30 amps or more at 60Hz that heat > and fail at 4-5 amps at 10 MHz. > > 73 Tom > > > _________________ Topband Reflector Archives - http://www.contesting.com/_topband
