Connectivity

[golson]

Hi,

  I have been looking for information on what cables I need to buy for connecting GTX Rocket IO SMA s together on my ML510

board.  I took a look at the Digikey catalog and found several possibilities but there are different cable types also.

There seem to be coaxial cables such as:

SMA plug to SMA plug

RG-178

RG-316

RG-316DS

RG-58

I am interested in HD-SDI  SD-SDI ect.

Any suggestions for the type of cable here.

I am looking at Emerson Fixed Length cables and adaptors on Page 478 (us2010) catalog.

Thank You,

  Gary

[mcgett]

In order to connect with the Female/Jack SMA connectors on the board you will need to have a Male/Plug SMA connector on the cable.

The RG-### that you listed denote different coax cable construction types.  The primary concern when reviewing the coax cable specifications is that it will provide a 50 ohm impendance and that the rated frequency is at least each to the bit rate that you are sending.  So if you are planning on using a 5.0 Gbps bit rate then you should have at least a 5.0 GHz rated cable.

The last concern is length tolerance between two cables.  You should make sure that your length difference does not exceed more than 0.10UI. So in the previous 5.0 Gbps example this would be a 200pS bit time and 0.1 UI is 20pS.  Most coax will have a velocity factor of 0.65 to 0.85 factor, so with an average of 0.75 this would  0.75 * 300*10^6m/sec * 20*10^-12 sec = 4.5*10^-3 meters or 4.5mm.

Most companies will likely not give you a specification for pair skew without placing a custom order, so the next best alternativeis placing and order for multiple cables and then selecting the closest match from what you receive.

[golson]

Hi Mcgett,

  Thank you for the information.  there seems to be a lot to consider in buying cables.

  Do you know of a good cable manufacturer or part number .  I am looking at some cables on the internet but have not been able to find cables that say straight out that they support 5 gbps.  I went to l-com web site which specifies db loss per meter at specific frequencies.

Thank You,

  Gary

[mcgett]

I'm traveling and can't look up specific part numbers, but the cables in the MGT kits should have been sourced from Florida RS Technology and these have held up well over the years.

Keep the total loss in the cable to less than 6dB at the frequency of interest and you should have no issues.

Note: I used 5Gbps as an example only.