Francesco, we cross posted.
If not EECL, what?
The most intriguing behavior is "External counter input works OK in the 0-10Mhz range, but doubles
the reading in the 10-512Mhz range (BUT not if signal is coming from output REF (rear panel) !!"
I'll double check the band switch wipers... they seem in place and none found floating inside the instrument..
Emanuele Girlando