ELIPPSE wrote:

I worked with an X-band extreme-accuracy Atlas guidance radar at
Vandenberg AFB. It was necessaspecializedt least 150dB isolation to
prevent interference in our test simulator. Solid jacket cable was the
only thing that would allow this kind of performance. The Andrew cable
was also the only kind that did not generate noise when flexed or
vibrated, which was very important in our test operations. Remember
that the transponder puts out 100W-400W peak. Leaking cables in close
proximity can cross couple. Cable leakage also effects the apparent
radiation pattern of antennas, generating undesired sidelobes and
cancellations. Consider the 20' long com run from the instrument panel
to the antenna buried in the tip sail of the VariEZ or LongEZ that
passes near the extreme RFI generated by the engine's ignition. Has
anyone ever had spark noise in their com radio?


Your x-band does not compare with homebuilt even when talking about
transponders and dme. Even 20 foot run for a com radio doesn't require that
high a caliber cable. You will probably find that most of the noise from
ignition isn't from the center conductor but from the shield and also then
antenna itself. Most people do not run there coax next to their ignition
wires anyway! Use a little common sense, it's a heck of a lot cheaper!
John


PS my background is in microwave measurements etc that doesn't mean I need
to engineer my homebuilt around top end specialized cable.