We've added a series capacitor to the SNA600 to make it the "a" version. The previous version was a DC short to ground. This new capacitor makes it easier to use with the Venue receiver or others that provide a DC bias on the antenna port for powering remote, amplified antennas.
Actually, the capacitor can be added with a little care to previous SNA600's. Any surface mount ceramic capacitor from 100 pF to 1000 pF can be used. If you need the cap, send name and address to larryf@lectrosonics.com for a freebie.
If we had had our Lectro heads screwed on tight, we'd have put the cap on the original design.
Best Regards,
Larry Fisher
Lectrosonics
p.s. It does not affect the antenna RF performance, good or bad.