High speed differential connectors

[qwaarjet]

I have project that requires me to pass a 200mhz differential signal through a bulkhead (HOTLink II). The nominal impedance for the diff pair is 100 ohms and will need to travel ~3m. I have complete control over termination style and cable type; I was thinking either a rj45 cat7 bulked or possibly two 50ohm RF connectors like sma or similar and use 1 for each side of the diff signal. I would like to keep the cost relatively low <$100 ( connectors and cable) so twinax was out. Any better suggestions or just go with cat7?

[Stonent]

CAT 7 seems overkill since CAT 5e is rated to 350MHz, unless there's some other characteristic in CAT 7 that you're needing.

[Dago]

CAT 7 seems overkill since CAT 5e is rated to 350MHz, unless there's some other characteristic in CAT 7 that you're needing.

If the frequency of the differential signal is 200 MHz then it contains frequency components way way higher than 200 MHz, since it is not a sine wave.

[fcb]

Hotlink - there's a blast from the past.

I would look at CAT5 and upwards.  3M isn't that far - test it.  Also, you could consider USB3 connectors and cables, just use the D+/D- lines.

[ejeffrey]

Cat5e is only rated to 100 MHz, and used with signaling rates of 125 MS/s in fast and gigabit ethernet.  For a 3 meter run it will probably work fine at 200 MHz -- the loss is just too high for long runs like ethernet is expected to work over (typically 100 meters).  Cat 6 works for 250 MHz, Cat6a is rated for up to 500 MHz.  Cat 5 and 6 are normally unshielded, but also available shielded.  Cat 6a is always shielded.

[miguelvp]

Just 3 meters? You probably can re-purpose an hdmi shielded twisted pair (100 Ohm).

A network cable (even Cat 5 shielded) might do, after all 1000 Base T only requires Cat 5 for pretty long lengths so 3 meters should be fine too since it's rated for 100 meters, and it's 100 Ohm rated as well.

[David Hess]

Just to keep in mind how well balanced transmissions line works, here is a photo from inside of a Tektronix 100 MHz oscilloscope showing a pair of 100 MHz differential transmission lines.  Normally the wires are attached inside the connectors but I had to resolder them.