Thanks Bill.

The autopilot service manual I have shows a hand
drawn figure of the cable that indicates a curly or spiral twist
to the center conductor which appears as you stated to help
keep the center conductor in the middle of the tube. It also
mentions that the characteristics and length of the cable is part
of the tuned circuit, but doesn't give any data on the cable.

Like you, I'm sure I've seen that type of cable somewhere in
the past and thought it was in an automotive antenna application,
but it could have been elsewhere.

Ronnie

"- exray -" wrote in message
...
Michael A. Terrell wrote:




It was RG62 93 ohm coax.

Certainly not in older radios. I don't know what they sell nowadays.

I've seen that 'spiral' type of cable. They basically used the spiral as
a means of maintaining the centre conductor in the average 'middle' of the
hollow dielectric.

The combined inductance and capacitance of the old cable was somewhat
critical but the older radios provided an antenna trimmer to compensate
for the variations. The electrical model was essentially a "voltage
probe" and doesn't necessarily follow common antenna/feedline rules and
thought.

-Bill