Matt,
why would connecting two channels of the TIU together kill the signal ... Or is the duplicate data packets what kills the signal?
Nothing "kills" the signal. The signal strength is a computed value based on the percentage of packets, out of 100 sent by the TIU, that the engine receives and acknowledges.
In the case of two TIU channels that are connected to the same track, it's the engine receiving multiple virtually occurrences of the exact same command nearly simultaneously that has an adverse effect on executing a command.
There's a discussion of how DCS signal strength is calculated during a test in The DCS Companion 3rd Edition on page 58:
DCS Signal Strength
DCS signal strength is a number, from 1-10, that's calculated based on the number of data packets that the TIU sends and receives back from a DCS engine that's performing a DCS signal strength test.
During the test, the TIU sends a continuous series of data packets to the DCS engine. The DCS engine is expected to reply to every packet that it receives, however, some packets are either not received by the engine or the response is not received by the TIU. Regardless, the TIU calculates DCS signal strength by counting how many response packets the TIU receives from the DCS engine out of each hundred data packets the TIU sent, and then looks at a sliding scale to determine the signal strength that should be reported. The scale is not linear, rather, it is such that 87-100 packets equates to a DCS signal strength of 10, 80-86 equates to a 9, and so on.
When using a DCS engine to measure the DCS signal strength on a particular section of track, the engine will report some value from 1 to 10. If DCS signal strength is exceptionally low, an error message may be displayed instead of a value. A value between 8 and 10 is generally described as strong, between 6 and 7 is generally described as adequate and from 1 to 5 is described as low. While many operators strive for a consistent DCS signal strength of 10, it's a proven fact that nearly all DCS commands will operate just fine when DCS signal strength is 7 or higher.
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