I'm surprised at these reports, but not too much except for the 2 dB
connector. It must have had some internal corrosion, or perhaps something
like a helical internal contact causing an impedance mismatch that would
look like loss in a matched measurement system. (Some el crappo UHF barrel
adapters have found to be constructed that way.) I've seen some awfully
shoddy BNC connectors at ham conventions and wouldn't use them for
anything at all critical. But the OP asked if there was a place he could
find the losses of various kinds of connectors. I don't believe there's
any place you can go to find the losses of shoddily made or improperly
assembled connectors or adapters. Decently made and properly assembled
connectors of standard types show no appreciable loss at 1 GHz. If loss is
a concern, my advice is to buy name brand connectors, and especially avoid
the cheap stuff you see at places like flea markets.

Roy Lewallen, W7EL


Even at 1GHz, I don't believe that you would get as much as 2dB of loss
even if you joined two pieces of coax by stripping the ends with a knife,
twisting the conductors together, and wrapping them in scotch tape.
--
Ian

The items in question were SMA barrel adaptors and as I said showed no signs
of damage, corrosion or spreading of the contacts and interface dimensions
were in spec

It is surprisingly easy to get significant loss at 1GHz and above, 2dB would
be very easy to achieve even when using what appears to be a 'good'
connection.

regards
Jeff