LONDON, GBR: With the current concentration of broadcast media preparations for the summer games in London, Bryant Unlimited have extended their own-brand range of 75 Ohm digital coaxial video cables for high definition imaging for use up to 3Gb/s - 4.5 GHz.
Bryant has added the following new designs:
- BD SD50/53 - SDI video cables (medium)
- BD SD50F/53F - Flexible SDI video cables (medium)
- BD SD10/13 - SDI video cables (large)
- BD SD10F/13F - Flexible SDI video cables (large)
These cost-effective, European made SD-SDI, HD-SDI and 3G-SDI cables are constructed with gas-injected insulation, dual braid and tape screening and LSOH or PVC jacket materials to match the dimensions and performance levels of similar offerings.
Digital video cables must be dimensionally stable because any change in the designed distance between conductors and screen will alter the capacitance, hence, the impedance and the resulting return loss. Choice of insulating material is important because in a screened video cable, the insulator is the capacitor dielectric between core and screen and, the lower the capacitance; the less time it will take a signal to reach full amplitude.
Bryant broadcast high precision video coaxes have all been designed to provide maximum bandwidth, stable impedance, low attenuation and low return loss to match the best in show. They have been independently tested to guarantee HD performance and maximum cable length at HD-SDI (1080i) and exceed 3G-SDI (1080P SMPTE424M) with added legroom.
Bryant stock matching connectors for the whole cable range.
- BD SD01 coaxial cables are designed for the transmission of HDTV and serial digital video signals and are equivalent to Image 360 and Belden 1855 ENH, and like all Bryant's video cables have double shielding (one foil / one tinned copper braid). Digital signals include both high and low frequencies ~ braid screens are very effective below 10MHz and tape screens at higher levels;
- BD SD11 coaxial cables are an excellent low loss design with superb bandwidth and low capacitance and are equivalent to Image 1000 and Belden 1694 ANH;
- Used in 3GHz HDTV and longer runs of Serial Digital video signals, BD SD50 coaxial cables are of the same design and construction as SD01 and SD11 but lie between them in transmission ability and are equivalent to Belden 1505A.
Responding directly to customer demand, Bryant have developed BD SD10F and BD SD50F, which are flexible versions of the above with stranded centre conductors and PVC outer jackets for continuous deployment on cable reels. These new PVC jacketed versions are not designed as infrastructure cables, but have been developed for outdoor applications where repeated flexing would otherwise cause damage to the normal solid centre conductor and braided shield.
Serial digital interconnect standards for calculated max. cable transmission length:
- SMPTE 259M (PAL, widescreen): Maximum length = 30dB loss at half the clock frequency;
- SMPTE 292M (HDTV): Maximum length = 20dB loss at half the clock frequency.
This gives one method of defining the maximum calculated length of cable that provides satisfactory signal transmission. As the quarter wavelength of digital video is around 1,500 times smaller than analogue, reflections caused by BNC connectors in the digital chain will affect return loss and attenuation.
Bryant's Technical Manager Simon Quill said: "Return loss is not just down to cables. Impedance mismatches from unsuitable connectors and patch bays can lead to signal reflections at high frequencies, so the use of 75 Ohm BNCs is crucial and can alter manufacturer's claimed performance distances. Cable manufacturers tend to claim distance based upon differing parameters, which means the figures are often expressed on an apples vs. pears basis."
"Bryant tends not to make such statements since cables in broadcast applications are seldom installed to their maximum claimed length. Rather, we test all manufacturers' cables independently, so that we can be sure of their worth."