An update on EMC debugging (with BB60C).
We had a particularly troublesome HDMI port and due to the frequencies involved in measuring it, a lack of a suitable BW oscilloscope for signal ringing, eye-pattern and jitter analysis. Not to mention suitable differential probes…
I was looking at making some coupling transformers with a couple of secondaries such that I could connect them in-phase and out-of-phase to get differential/common mode signal levels. Again the bandwidth of the signal proved problematic for suitable magnetics.
However I recalled an article I found some time ago, which uses a hybrid coupler to transform a differential pair input into two single ended outputs – one differential mode, the other common mode. So after hacking some short SMA pig-tails onto an HDMI connector (also made a USB and Ethernet one) I then just connected up to the BB60C and had the HDMI display a fixed image. This gave me a defined spectral content signal. Then I just displayed that test signal on the two iterations of PCB layout and observed the drastic reduction a carefully considered layout makes…
