Why is my IP-708 transmitting at an excessive differential voltage level, beyond the specified valid range?
This is almost always caused by improper cable termination or coupling. The IP-708 is running on a MIL-STD-1553 bus, which should always be terminated at each end with a terminating resistor. Condor does not provide terminators with our products, but they are commercially available.
The 708 bus must be properly terminated for either Direct or Transmformer coupling. The default coupling on the IP-708 is Direct. However, you cannot wire straight to the LRU. This does not provide proper termination and results in unpredictable signal amplitude. For proper Direct coupling you should create an ARINC 708 bus using Triax cable, two Triax T-splitters, ~78ohm terminators, and stubs to each hardware device.
- Each stub should be less than 1 foot from the IP-708 and LRU connections to the bottom of the each T-splitter. A ribbon to triax stub for the IP-708 should have been provided, but you have to make your own for your LRU.
- A triax cable should extend from one leg of the T-splitter to the other (pretty much unlimited length there).
- A 78-ohm termination should be placed on each unused leg of the T splitter connection.
Transformer coupling should only be required if the cable leg "stub" from the IP-708/LRU to the splitter exceeds the cable length provided (approx 1 foot). For Transformer coupling, the stub length can extend up to 20 feet.