Topband: Engineering ?? @ relays

[Ford Peterson]

I'm still on the hunt for a decent set of relays for a remote matching network.  My goal?  1.5KW remote switching box.  I went to a local surplus emporium in Minneapolis to scour the junque boxes for decent relays.  Eureka! A boat load of 12v relays!  10A, breakdown voltage of 2KV between contacts, and 4KV between contacts and coils.  12v switching.  DPDT and DPST styles.  Visual inspection shows a good 0.050" to 0.060" air gap on the contacts.  I selected an Aromat JC2aF-DC12V.

Tonight, I decided to examine them in more detail.  Aromat spec sheet says 0.1 ohm on the contacts.  Contacts are silver alloy.  Maximum switching power 2,500VA.  MTBF 10^5.  Kewel!  They look perfect.  They are cheap $4.  They are small open frame styles with short RF paths of copper strap material.

I soldered RG174 cables to the contacts to switch both shield and center.  One cable went to a 50 ohm load, the other to the Autek VA1.  Open!  Switch the relays about 50 times and then they start to work.  I can see that the contacts are closing alright.  But no RF gets through.  So I took a stray JA QSL card laying on the desk and ran it through the relay contacts.  Then they start to work.  SWR reads 1.12 :1.  Close enough.  But unreliable.  They don't always connect--especially on the Normally Closed side of the relay.  Repeating it with another relay yields identical results.

Theory 1: These are designed to be hot switched.  The tiny arch from a hot load fuses the contact.  Stop worrying about it.  Push some decent power through them.  They will fuse and be just fine.

Theory 2: My gut tells me that a robust design would include a self cleaning wiping action on the contacts, like on a band switch.  I will not get reliable switching using traditional relays.

So how does Ameritron get reliable connections?  And Com-Tek with their phased arrays?  Are relays unsuitable for this application?  Should the contacts be gold?  What am I missing here?

Any help the engineer types can provide would be appreciated.