Thanks Roy. Now that you mention it, I do remember
the straight center conductor inside the much larger diameter
PE tube. 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 to help keep the center
conductor in the middle of the tube. I 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.

The connectors are like the connectors that were on the auto
radios back then. I wonder where those could be found today.
I can't seem to find them in any of the distributor catalogs I have.
Maybe a trip to an automobile junk yard.

Ronnie


"Roy Lewallen" wrote in message
...
The coax used for every car radio of that vintage I ever saw (and I saw a
lot) doesn't fit your description. It had a single, small diameter (#28 or
so) wire rattling around loosely in a thin polyethylene tube, which was
covered by a braided shield. The objective was to minimize the
capacitance, but there obviously wasn't any control over Z0 or delay,
since the small wire was free to move around inside the much larger
diameter PE tube. There was no helically wound conductor. I think you
might be looking in the wrong place for what you need. The connector fits
your description, though.

Roy Lewallen, W7EL

Ronnie wrote:
Hi,

This is not about ham radio, but rather a general question
about the type of cable and connectors that were found
between the antenna and the AM radio in GM cars in the
60's. I'm trying to locate some technical information about
the cable and a source for the cable and connectors.

I have an old airplane autopilot system that uses tuned circuit
to sense changes in the airplane's attitude and the position of
the control servos. Distributed variable inductances and
variable capacitors combine to establish the resonant
operating frequency of the system. The components are
connected together with specific lengths of cable and the
service manual points out that the lengths are critical because
of the added capacitance of the cable and connectors.

The cable is marked as follows:

"I. T. & T. Federal Cable R.E.C."

It is a shielded cable with a spiral wound center conductor
that looks very much like the antenna cable I remember finding
in GM cars in the 60's. It also has the same type of connectors.
There is a center pin for the center conductor and a metal sleve
that extents back over the cable and makes a connection with the
shield and chassis of the radio. Friction holds the connector in
its mating socket - there are no threads, just a couple of splayed out
areas on the sleve.

I was hoping one of you might be able to point me to a source
of technical information about this cable, such as the capacitance
per unit length, etc. The one piece I have measures about 10.5 pF / foot
or 415 pF / meter, but my measurements may not be all that accurate.

Also, a source where the cable and connectors can be found today
would be appreciated.

Thanks in advance for any help.

Ronnie, N5CSE