On Friday, December 18, 2015 12:27:33 PM Charles Steinmetz wrote: > Poul-Henning wrote: > >A significant reason for the TADD-1 existing in the first place was to > >break groundloops. This is incompatible with tying all the BNC's together. > > It is perfectly possible to ground coax connector bodies at RF > without grounding them at power-line frequencies (and expected > harmonics) or DC. Indeed, that is what the TADD-1 attempts to > do. The BNC bodies are connected to the enclosure with 10nF capacitors. > > However, the implementation in the TADD-1 is not as ideal as I'd > like. The bypass isn't directly to the enclosure, but rather to the > ground plane of the PC card, which appears to be connected to the > enclosure only by fasteners at the corners of the PCB -- some inches > away from the BNCs. That is why I will almost never approve a design > that uses isolated, PC-mount coax connectors. The loop from each BNC > body, through the capacitor, to the enclosure should be no more than > 1/2" (~ 1cm) long, preferably less.
Something like an annular ring capacitor that insulates the BNC body from the chassis whilst capacitively shorting it to the Chassis at RF ??. Followed by a freeite sleeve/bead arround the connector body or the coax connecting the signal from the connector to the PCB? > > I like to add a resistor in parallel with each capacitor, to shunt > any unexpected DC or LF leakage current. This resistor needs to be > large enough (in value) to limit any circulating ground currents to > low values that will not cause significant voltage drop in the > shields (i.e., ground loops), but at the same time will effectively > terminate any expected leakage currents. Generally, this will be > from 10 to 100 ohms, depending on the sensitivity of the most > sensitive inputs in the system and whether guarding is employed. > > Best regards, > > Charles > > Bruce _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.