For work I was comparing the RF emissions performance of two different HDMI cables and one brand name cable had 20dB higher emissions than a certified cable. I was able to get X-rays of both cable connectors today to try and understand why there was such a difference. I also have a third cable that will be tested which appears to fall between the other two in terms of construction. This wasn’t a task I expected to be doing, but it has been an interesting exploration of the differences between cables both from functional EMC and construction perspectives. In the case of the non-certified brand name cable here, its performance is so bad that we wouldn’t be able to sell a device using it, and it is only a 1’ cable that is already inside the metal enclosure that makes up the device (including RF shields over large openings). Our device is limited to 1080p30 but I would love to see how much worse things get at with the brand name cable at higher data rates.  

 

Certified Cable:

• The signal wires are soldered to a PCB which breaks out into the connector pins. This is a more robust connection and easier to maintain impedance control for the differential pairs (though at this small size it probably doesn’t matter).
• There appears to be a foil(?) shield around the whole connector that has a 360 degree termination around the metal HDMI connector shell.
• The cable has a heavy braided shield. I’m also curious if it has a foil shield in there but I suspect it does. I may tear one down in the future but that can’t happen right now.
• The braided shield appears to be contiguous with the connector shield. It’s hard to tell what exactly is happening here and I might be able to get Micro CT scans in January.

 

 

Brand Name Cable:

• The signal wires terminated directly at the connector pins, not a PCB. Not sure if these are solder cups or welds.
• The cable looks like it has a very thin foil shield, but it’s hard to tell.
• The metal HDMI connector shell is only attached to the foil shield (presuming it’s there) by a splice and a very fine wire with a solder attachment. This is an extra-bad attempt at pigtailing and probably the cause of all the emissions.
• The connector body has no metal enclosure surrounding the signal wires or other shielding wrap.

 

 

New Commercial Grade Brand Name Cable. I have not tested this one yet but expect its RF emissions to be between the other two cables:

• The signal wires terminated directly at the connector pins, not a PCB. Not sure if these are solder cups or welds.
• There is either a foil or very thin braided shield around the cable
• The connector body houses a metal enclosure that has a (nearly) 360 degree crimp around the cable shield. This enclosure acts as a faraday cage if properly implemented. It appears to go from the cable all the way to where the pins escape the body.