Great questions!
As far as cross talk, I think I can answer that one. It is my belief that our intercoms provided more "Volume" to the headsets due to our increased gain. If signals are small, while the same amount of cross coupling is present, the one with more gain will exhibit cross talk more pronouncedly because of the higher gain.
Capacitance in a capacitor is determined by the size of the plates, the type of insulator, and the distanced between the plates.
In this case, the plates are wires, the insulator is the insulation on the wires, and the distance the wires are away from each other.
Place two different signals and a common ground in a shielded bundle and the signals will couple together because of the inherent capacitance between the wires.
When we introduced our aerocom in 1985, we introduced two new things in the field of aircraft intercoms, individually gated microphone and more gain than any other intercom, at that time.
As far as why you don't have to use shielded wires, I don't know the answer to than one. I never had a need to disassemble one and look at how they did things. Maybe a Sigtronics representative could answer that for you, I would very much like to know that answer as well.
But please let me assure you, we have gone to great lengths to minimize RFI. And while I know it bares little importance to homebuilders that products are TSO?d or not, our intercoms are (except the PM1200 but is built exactly the same way as our others) have gone through a rigorous certification process. It includes susceptibility, emissions, and voltage spikes that are "coupled" with the entire bundle.
It's not easy to pass these tests, but we do and had lead us to a better products.
Long answer, but you had a great question.
Hope this helps.
Mark
Mark,
I don't ge this. I have a Sigtronics 200S in my RV and none of the wires they supplied are shielded. With over 250 hours on the plane I have had no problems of any kind.
What is different about this intercom that it doesn't require shielded wires?
