Balanced to unbalanced audio - wiring?

Simon, one of our wiremen asked me the following question;

...why do we always cut-back the black core when wiring FST into RCA (phono) connectors?

Back when all broadcast gear drove balanced lines with a proper rep-coil (a 1:1 audio transformer) you could safely bodge-unbalance a balanced line by shorting the cold to the screen and you get full signal across half of the sending rep-coil and everything worked. Nowadays not all equipment drives a balanced line this way - may bits of gear use op-amps to derived the +ve and -ve going halves of the balanced pair (via the inverting and non-inverting inputs - think 741 Op-amp). If you pull one of the signal cores to ground you effectively short one bit of silicon and it sits there warming up. That may not be a problem, but in the case of Avitel distribution amplifiers (well, after 1995) they driver stage burns out after a few months (long after the SI engineers have left!). This exact problem bit my backside when I worked at Oasis TV and all the monitoring switchers in the machine room had unbalanced inputs.
The only downside of using my method is that you loose 6dBs of level, but probably into a piece of equipment that wasn't calibrated (like a DVD recorder or TV). I think that's a worthwhile compromise to avoid the possibility of frying the backplane on audio distribution amps (or suchlike).

A trip down misery lane

Here are a few pictures from the original install of Oasis Television's building on Great Pulteney Street. Remember when edit suites cost £500k and had many pieces of equipment that all had to talk to each other! I'm the fresh-faced chap on the right of the sofa and the other chap is my old mucker Chris Clegg. The other reprebates were my wiring team - Amos and Jim are still in the industry and Tony (on the right) is sitting behind me in the workshop today! Both of us have more grey hair now.

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!

From the sublime to the ridiculous

We've been doing an install at a Soho facility and as ever Tony and the wiremen do a superb job - neat and accurate. The right-hand image shows our cabling on the top cable tray and the previous systems integrators efforts below; Un-numbered cables that have been just thrown in. They've attempted to run HD-SDi over skinny coax and fibre channel over long pre-made tight-buffered optical cable. By contrast we do all video on Vision 1000 and all fibre on kevlar-armoured loose-tube cable. I'm amazed that previous company had the cheek to submit an invoice!