Topband: QST article (May 2009, p 66) on antenna relays

[Niko Cimbur]

Rick,

  I have used the open frame relays you describe in several remote tuner projects over the years, and they worked really well. With the original contact spacing and with 1500W power output I never observed any arcing problems.  With the stock relay spacing the voltage between the NO contacts breaks down at around 6 kV. The impedance in question would have to be quite high to get there at 1500W. 

One of the other issues with them is hot switching the relays, and in turn slowly destroying the contacts. (I have never done that of course).  

 I live close to the coast, and the biggest problem with my application became corrosion.  All of the exposed metal eventually corroded, so I migrated to HC-1 or RJ-1 vacuum relays for my antenna tuners and switching applications. I never had one of these vacuum relays fail so far.  

 I have a fairly large stock (100+) of HC-1 or RJ-1 vacuum relays to pick from,  some NOS, some pulls.  I HI-potted them all. Upon testing them I had many failures, even the NOS ones, so anyone buying these relays better beware, you could be buying junk! (Reminder to myself: sell the failed relays on e-bay, as-is, condition unknown.)  I also observed the breakdown voltage to be quite different for similar relays, all over the place up to 6 Kv +.  Most crack in the 3.5-5 kV range, the ones under 3kV I don't use.  

Comtek has been using a T92S11D22-12 in their later switch boxes.  It is a sealed relay with high current rating, and quite inexpensive.  Allied has it for around $11.

Niko - AC6DD