Testing Equipment and Procedure

Since this isn't something just anyone can do, we felt it only appropriate to really explain the testing equipment and exactly how the tests are carried out. Due to the sensitivity of the measurement system and the frequencies involved, you can't simply hook up these cables to an LCR meter and measure resistance, capacitance and inductance. We're dealing with rise and fall times of individual bits in a signal that is sending (in our case) up to 5 BILLION of these bits every second - and that's just over a one of the pairs of cables. There are four basic components to the testing system we utilized: the signal generator, the HDMI test probes, the scope, and the software which ran the tests and provided more detailed results.

The signal generator was an Anritsu Pulse Pattern Generator (model MP1763C for you propeller heads). This sent a signal to an HDMI Test Fixture which we attached to one end of an HDMI cable to be tested. The other end connected to another Test Fixture which then fed into the TDT/TDR Sampling modules of a Tektronix DSA 8200 Digital Serial Analyzer. The signal generator costs around $84,900 in its stock form, the test probes are around $12,000 each and the base price of the Tektronix Analyzer/Scope is $25,000 with the TDR modules costing another $18,000 each. If anyone reading this is interested in doing these tests on your own, simply put your house up for sale and you might be able to afford the required equipment. We felt very fortunate to be able to use a system provided by Monster Cable (they actually have a spare, believe it or not). Check out the parts list and pricing of what a fully-equipped rig costs:

• Tektronix DSA 8200 Digital Serial Analyzer, $25,000
• 2 x Tektronix 80E04 TDT/TDR Sampling Modules, $36,000
• Anritsu MP1763C-1 Pulse Pattern Generator, $85,000
• Digital Serial Waveform Analysis Software, $20,000
• HDMI Test Fixture Calibration Kit, $5,000
• 2 x HDMI Test Fixture TPA-R adaptors, $24,000
• 4 x 20" RF Coaxial test cables with SMA connectors, $1,600
• 2 x 36" RF Coaxial test cables with SMA connectors, $1,000
• 18 x Precision SMA 75-ohm Terminations, $7,200
• Agilent GPIB/USB Interface, $700

Grand Total = $205,500 (not including the laptop to run the software)

Once the system is properly configured, testing is a very straightforward process. The general idea is that you are looking to see how well the cable allows for the individual bits, in the form of 1's and 0's, to be resolved by the system. Once a cable exceeds its spec (goes further than it is rated), the rise and fall times lose definition and the test fails. The way we look at this is through the use of an eye pattern. The eye pattern is a rectangular box which resides within the rise and fall time of a set of bit transitions.

A passing signal

When the rise and fall time take on a more gradual slope, we note this as jitter - something every cable will reflect (see above). When the pattern eventually intersects the center eye, or rectangle, we say the cable has failed.

The signal goes "squish", like grape. This doesn't mean it won't pass real-world, however.

The amount of variance in the system is shown by the thickness of the lines making up the pattern. Some cables had a medium thick line, and some had very thick lines. Many cables with higher variances were prone to failing earlier, but this wasn't an absolute indicator by any means. If you'll notice, each bit is only part of the whole signal which makes up the picture. That means that an HDMI cable can show gradual or partial degradation. That's how you get snow and 'hits' on an image instead of having it simply shut off.

We were only able to run tests on analogue cables, so we had to put aside our active HDMI cables since we didn't have the correct sampling modules for that job (We were going to spring for the extra $72,000 in active-ready modules but we left our credit card in our other pants...)