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HD video transmission over RG-59 cable

14 Jan 2013  | Daniel Ogilvie

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The reconstructed sine and cosine waveforms are multiplied by the input 148.5MHz free-running composite video. The output of the sine channel is the demodulated U signal and the cosine channel is the demodulated V output.

The output of the demodulator also comprises twice subcarrier frequencies. The output is therefore low-pass filtered using a 63-tap filter, the response for which is shown in figure 4. The output of the filter is the clean 'simple' demodulated U and V.

The low pass filtered luma is conditioned by the processing amplifier. First the black level offset is subtracted from the luma signal to set the black level at zero. The luma is then amplified to provide a 960 code (10 bit) output for a 100% white input. The luma output is sampled at 74.25MHz.

The low-pass-filtered chroma outputs are amplified separately to provide a nominal 700mV output for a 100% colour bar input. These outputs are valid on the rising edge of the 74MHz clock when the Cmux (37MHz) enable signal is high.

The SPG also provides Vout (vertical) and Hout (horizontal) synchronising outputs which can be used for later processing blocks or for a digital to analogue converter.

HD-CVI evaluation platform

An evaluation platform for the HD-CVI interface has been developed to prove the concept. A small transmitter and receiver module have been developed and the encoder and decoder have been written in Verilog and compiled for an Altera Cyclone III FPGA (EP3C25).

The interface has proven reliable over 300m of RG-59 cable with a frequency response to 30MHz ±0.2dB being achieved.

Figure 8: This is a screen capture of the output of the HD-CVI receiver. It shows a 30MHz sweep waveform after transmission across 300m of RG-59 cable.

Further work is proceeding on lowering the BOM cost, increasing the cable distance and transmitting 1080p/60Hz video.

Conclusion
I would be the first to complain against the proliferation of unnecessary standards or worse, the abuse of existing standards.

However, the increasing use of HD video cameras in the surveillance market has created a problem for the transmission of the same standards.

A large number of buildings have already been cabled for security, but using RG-59 cable with the expectation those cameras would be standard definition and existing methods of transmitting the video uncompressed are not compatible with these installations. Even for future installations either multiple cables or more expensive cable/repeaters will be required for the transmission of HD video, adding considerably to the cost of the installation.

The interface described above allows the transmission of HD video using RG-59 cable over distances of greater than 300m with very little degradation. The transmitter adds minimal cost overhead to the camera whilst the receiver up cost is expected to be comparable to adding HD-SDI. These costs could of course be mitigated by the development of an ASIC.

About the author
Daniel Ogilvie is Technical Director of SingMai Electronics and has been involved with electronics, both at an amateur and professional level, since he was sixteen. Daniel has worked for both large and small companies as well as owning and running his own U.K.-based company for eleven years. He has worked for companies in such diverse fields as university physics research support, high-end broadcast video, DVD recorder front end semiconductors, video decoder IC design and high volume consumer electronics in countries as diverse as Canada, USA, UK, Thailand and Singapore.

Products that Daniel has been involved in include forensic glass refractive index measurement equipment, (occasionally featured on the US TV program CSI), very low-light photon counting video processors, broadcast quality FPGA based video decoders, very high resolution real-time video processors and IC design of video input processors. Daniel is a senior member of the IEEE.

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