Thursday, January 17, 2008

HD over standard def coax

People often ask me about this and I normally repeat the received wisdom - you get away with it over short runs etc. etc. BUT, I didn't realise how close to the hairy edge sending 270Mbit SDi over Image 360 was. Look at the chart - I assumed that (as per most bandwidth calculations) that a cable designated Image 360 would have better than 6dB of loss at 360Mhz over 100m (the spec) - but no - worse than 16dBs down at 100m (almost down to an eighth of the signal level). I suppose it is testament to how good drivers/receivers and error recovery schemas are.
Now - imagine that you're sending 1.48Gbits per sec. That's two and a half octaves extra bandwidth above SDi - so probably another 12dBs of loss - so over Vision 360 you're looking at 30dBs of loss over 100m! Even over short distances it is a miracle that HD-SDi goes over normal coax.
Blogging on the train on the way to Leeds - free WiFi!

No comments: