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Bnc for timecode - Ohms


PTA

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You're talking about standard LTC?

I can't imagine any situation where the cable impedance would matter. That stuff - and all modern equipment using it - is designed to be incredibly robust. It can survive the address track on a 3/4" tape or even a phone call!

Standing-wave jitter, rolloff, and other impedance gremlins can affect high speed data like s/pdif coax or Ethernet (or does anybody remember SCSI?), and cable impedance is important in some analog audio and most RF situations... but AFAIK, not timecode over the kind of cable lengths you'll find in a shoot or a studio.

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No one has mentioned the two common varieties of BNC connector. They are controlled impedance connectors and come in 50 Ohm and 75 Ohm. The 75 Ohm one has a smaller diameter centre pin. The consequence of this is that if you use a 75 Ohm plug with a 50 Ohm socket the centre pin may not make contact and your connection might be intermittent. More damaging is using a 50 Ohm plug with a 75 Ohm socket as the centre pin contacts on the socket can end up being permanently splayed out, so a subsequent 75 Ohm plug to damaged 75 Ohm socket may also become intermittent.

 

I'm currently trying to get definitive information from Zoom about which they use on the back of the F4.

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On 2/19/2021 at 11:44 AM, Michael Addlesee said:

No one has mentioned the two common varieties of BNC connector. They are controlled impedance connectors and come in 50 Ohm and 75 Ohm. The 75 Ohm one has a smaller diameter centre pin. The consequence of this is that if you use a 75 Ohm plug with a 50 Ohm socket the centre pin may not make contact and your connection might be intermittent. More damaging is using a 50 Ohm plug with a 75 Ohm socket as the centre pin contacts on the socket can end up being permanently splayed out, so a subsequent 75 Ohm plug to damaged 75 Ohm socket may also become intermittent.

 

I'm currently trying to get definitive information from Zoom about which they use on the back of the F4.

All BNC connectors manufactured to current specs will mate non-destructively. Sound Devices and all cameras I’ve bothered to check use 75 ohms for TC. But to reiterate what everyone else said, at the lengths we typically use it doesn’t matter. 

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