Coaxial cable is constructed in an "axial" configuration, as shown in Figure 1 above. This type of cable is widely used in video applications, and is available in a myriad of types from many manufacturers. Putting connectors on the ends of the coax cable ("terminating" the cable) is not overly difficult, although the majority of BNC-type connectors for coax are "crimp-on" connectors, requiring a special crimp tool and appropriate crimping "die" for the tool fitting the specific cable and connector chosen.
Return to Top
2. What is triaxial cable?
Triaxial cable (typically referred to as "triax") contains three electrical conductors – a "center conductor" running down the middle of the cable, an "inner shield" consisting of a wire mesh inside the cable, and an "outer shield," another wire mesh around both the center conductor and inner shield, but beneath the outer covering of the cable ("jacket"). Between each conductor is a plastic or foam material called a "dielectric" which insulates the conductors from each other and maintains a specific electrical "impedance" for the cable.
Triax is constructed as shown in Figure 2 above. This type of cable is typically used in remote production environments, where multiple signals (multiplexing) are transmitted to/from a camera, using a triax control unit and triax adapter-equipped camera. Because there is an extra outer shield for safety, triax cables used with professional camera systems often have voltages in excess of 100 VAC present on the center conductor and inner shield while in operation. Special triax connectors are required, and the termination of triax cable is best left to someone with the necessary training and tools.
Return to Top
3. Why is cable selection important?
Cable selection is very important, as it determines the maximum length of multiplex cable (between the Pro-X1 control unit and Pro-X1 camera adapter) you may use. It is important to obtain the appropriate cable for your production system requirements, while keeping the weight and cost of the cable (and connectors) as reasonable as possible. In short, purchase the type and amount of cable you need now, but consider other potential uses in the future when filling your cable requirements.
The Pro-X1 Multiplexing System is designed to operate on coaxial cable. However, it will also operate perfectly well on triaxial cable (using the center conductor and inner shield of the triax). It will be necessary, however, to purchase triax-to-coax adapters to interface your Pro-X1 system to triaxial cable. While these adapters are not inexpensive, they will allow the use of your system(s) with triaxial cable in many cases. Camplex Corporation has these adapters available in a variety of types.
Return to Top
4. What type of cable may be used?
Any good-quality 75-Ohm impedance cable is acceptable for use with the Pro-X1 system – however, your choice of cable will depend greatly upon the maximum distance you need to operate. You will also need to obtain BNC-style connectors for the cable you purchase, which, in many cases, will require the purchase of a connector "crimp" tool to allow you to "terminate" the cable with a BNC connector at each end.
Return to Top
5. How far can I go on a given cable?
Power Distance
Basically, the Pro-X1 Multiplexing system can "overcome" a total of approximately 22 Ohms of DC resistance on any given cable, while still providing the necessary voltage at the input to the camera adapter box. Using this figure, and the DC resistance of a cable (determined by adding the center conductor resistance and the shield resistance at a specified length), it is then possible to mathematically estimate the maximum length possible on a given cable using the loop resistance figure.
Be aware that this distance is an estimate only – due to the "switch-mode" design used in the Pro-X1 Multiplexing system, and the switch-mode power supplies used in most modern cameras, there will be a certain point where the power provided from the Pro-X1 control unit is no longer sufficient to adequately power the Pro-X1 camera adapter. This length may vary depending upon the camera, accessories, and whether the camera will be recording during operation.
Signal Distance
Another important factor in determining the appropriate cable for a Pro-X1 Multiplexing system application is the "nominal attenuation" figure for a given cable. The Pro-X1 Multiplexing system has an overall "RF budget" of approximately 25 dB at 30 MHz. Extrapolating the attenuation of the proposed cable at 30 MHz (estimated in many cases or averaged using the manufacturer's 10 MHz and 50 MHz figures), Table 1 shows the distance at which 25 dB of attenuation is reached. Please note that this is only an approximation, and also note that, in most cases, the power distance is shorter than the signal distance (until you start using RG-11-type cables).
The chart below shows a sampling of some manufacturers' cables and the theoretical lengths that will allow full operation of the Pro-X1 system.
NOTE: The table above relates theoretical maximum lengths for a given cable. Be aware that DC resistance and nominal attenuation are affected by the temperature and condition of the cable, integrity of the connectors used, and other factors. As such, the maximum lengths shown may not be possible. Camplex Corporation recommends you reduce the maximum length of any given cable choice by at least 15%–20% for reliable operation.
Table 2 – Multiplex Cable Resources
Return to Top
6. Does Camplex recommend a particular cable?
Camplex Corporation does not manufacture multiplex cable but we can provide certain cable if required – the final choice of multiplex cable supplier and type is the userís responsibility.
Our sales personnel will be happy to assist you in selecting an appropriate cable type, based on information you provide. Please contact your dealer or Camplex Corporation for assistance, with the following information for each Pro-X1 system you intend to use:
a) Maximum multiplex cable distance required for your application,
b) Camera make/model to be used,
c) External viewfinder or other camera accessories to be used,
d) Will VCR operation be required (at camcorder?), and
e) Temperature range during operation (maximum and minimum temperatures) you expect to encounter during operation).
With this information, we can help you choose an appropriate cable type, length, and connectors so you can operate your Pro-X1 system reliably.
