I want to select the amount of differential cable delay between the top (4-port directional) antenna and the bottom (1-port Omni-directional) antenna in the TCAS II RBP-7G connector pin.

In the ACSS TCAS II installation manual, there are four options can be selected in the RBP-7G pin, which is only one-time configurable during the installation. They had given 0-51 nsecs, 51-120 nsecs, 120-200 nsecs, 200-350 nsecs.

I know how to calculate differential cable delay between two cables, which is done by subtracting the cable delays of the two cables. But my question is how to calculate differential cable delay between a 4-port (4 cables) top directional antenna and a single port (one cable) Omni directional antenna.

Is it right to calculate the difference between each of the directional port to the Omni directional port (or) we can just sum all the delays of the directional ports and then subtract the total delay of the directional antenna with the Omni directional antenna delay.

  • $\begingroup$ While this is installed on an aircraft, seems like it would be a better question for Electrical Engineering. $\endgroup$
    – FreeMan
    Commented Oct 10, 2023 at 18:59

1 Answer 1


Cable delay is identical on each of the 4 cables connected to the Directional antenna. In the ACSS system, the 4 cables are the same length and the delays ARE NOT additive. (Please forgive me for shouting!!)

For the calculation you are trying to make, take any one of the 4 upper cables, calculate for that single cable against the bottom Omni cable, and the job is done.

Good question.

  • $\begingroup$ That makes sense $\endgroup$
    – DeltaLima
    Commented Oct 12, 2023 at 0:24

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