Nope. That's where. Autos. A piece of spiral plastic "rod" around the
solid wire center conductor to space it in the center of the over-sized-hole
dielectric. I thought it was also a "Motorola" connector, but didn't want
to sound arrogant (still working at the circle M Ranch, you know). The AM
receiver antenna was (is) nothing more that a capacitive probe hooked to the
input, so the smaller the loading cap the better.
Gee, if I shill have some around, perhaps some experimentation to determine
the Z0 ... OK ... project 9,735, on the list for retirement. (yea, right)

73, Steve, K9DCI

I only saw it referred to as low capacitance cable. Don't know if the Z0
was specified
"Ronnie" wrote in message
. com...
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

- exray - wrote:

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

One of the engineers at Delco told me it was RG-62, and 93 ohms when
I was going to their annual car radio training back in the early '70s.
IBM also used RG-62 on their coaxial computer networking, but they used
BNC connectors.
--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael A. Terrell wrote:
. . .
One of the engineers at Delco told me it was RG-62, and 93 ohms when
I was going to their annual car radio training back in the early '70s.
IBM also used RG-62 on their coaxial computer networking, but they used
BNC connectors.

The automotive coax I'm familiar with isn't RG-62.

Like automotive coax, RG-62 has a thin walled hollow insulating tube.
But RG-62 has a polyethylene "string" which is helically wound around
the center conductor to keep it centered in the hollow tube. The coax in
every old automotive installation I've seen lacks this PE "string", so
the center conductor is free to flop around inside the hollow tube. The
effect of the "string" is to make RG-62's Z0 constant and predictable,
and it will also increase the capacitance somewhat. Constant Z0 isn't
important for the automotive application, and low capacitance is important.

It seems to me the center conductor is smaller in the automotive coax
than in RG-62, also.

Roy Lewallen, W7EL

Roy is right. I looked up RG62 and this is not the cable I have.
Here's what the autopilot service manual has to say about this
cable.

"The coaxial harness assembly CD-1, 2 and 3 is manufacued to specific
lenghts and since the cable is a part of the tuned circuit, these lengths
must
not be altered. The sensor leads are made of very fine wires that are fed
through a hollow insulator. Note that the fine wire has been coiled to
provide flexibility and reduce the possibility of beaking and causing an
open in the circuit."

The diagram shows a hollow tube with a fine wire that is coiled running
through it, a braid style shield over the hollow tube and an outer jacket
over the braid. It seems to be a variant of the auto coax where the fine
wire center conductor has been coiled instead of being left straight.

Thanks for all the help with this, but don't worry yourselves about it.
I have all the orginal pieces with connectors intact, but I was hoping
to find the technical specs on the cable so I could understand the
cable's impact on the resonant frequency.

Ronnie

"Roy Lewallen" wrote in message
...
Michael A. Terrell wrote:
. . .
One of the engineers at Delco told me it was RG-62, and 93 ohms when
I was going to their annual car radio training back in the early '70s.
IBM also used RG-62 on their coaxial computer networking, but they used
BNC connectors.

The automotive coax I'm familiar with isn't RG-62.

Like automotive coax, RG-62 has a thin walled hollow insulating tube. But
RG-62 has a polyethylene "string" which is helically wound around the
center conductor to keep it centered in the hollow tube. The coax in every
old automotive installation I've seen lacks this PE "string", so the
center conductor is free to flop around inside the hollow tube. The effect
of the "string" is to make RG-62's Z0 constant and predictable, and it
will also increase the capacitance somewhat. Constant Z0 isn't important
for the automotive application, and low capacitance is important.

It seems to me the center conductor is smaller in the automotive coax than
in RG-62, also.

Roy Lewallen, W7EL

Roy Lewallen wrote:

Michael A. Terrell wrote:
. . .
One of the engineers at Delco told me it was RG-62, and 93 ohms when
I was going to their annual car radio training back in the early '70s.
IBM also used RG-62 on their coaxial computer networking, but they used
BNC connectors.

The automotive coax I'm familiar with isn't RG-62.

Like automotive coax, RG-62 has a thin walled hollow insulating tube.
But RG-62 has a polyethylene "string" which is helically wound around
the center conductor to keep it centered in the hollow tube. The coax in
every old automotive installation I've seen lacks this PE "string", so
the center conductor is free to flop around inside the hollow tube. The
effect of the "string" is to make RG-62's Z0 constant and predictable,
and it will also increase the capacitance somewhat. Constant Z0 isn't
important for the automotive application, and low capacitance is important.

It seems to me the center conductor is smaller in the automotive coax
than in RG-62, also.

Roy Lewallen, W7EL


I saw both types on car radio antennas, and some was clearly marked
RG-62. Both types meet the original RG62 specification, they just use
two different methods to minimize dielectric losses, like fused disk
hardline used in CATV and other applications that require low loss
cabling. Also, why would one of the Delco engineers who designed their
car radios lie about the coax they used? He was explaining the then
brand new AM/FM/8-track combo when I asked a number of questions about
the RF front end. As usual, you will continue to believe whatever you
want to.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

Michael A. Terrell wrote:

I saw both types on car radio antennas, and some was clearly marked
RG-62. Both types meet the original RG62 specification, they just use
two different methods to minimize dielectric losses, like fused disk
hardline used in CATV and other applications that require low loss
cabling. Also, why would one of the Delco engineers who designed their
car radios lie about the coax they used? He was explaining the then
brand new AM/FM/8-track combo when I asked a number of questions about
the RF front end. As usual, you will continue to believe whatever you
want to.

I happened to find a piece of the automotive cable -- complete with
connector -- in my junk box, which I'm pretty sure was cut from a
replacement antenna probably purchased in the '70s. This particular
cable lacks the PE "string", but the ~#31 center conductor is crimped in
a sort of zig-zag shape to keep it in place in the hollow tube. The
aviation cable apparently has the center conductor bent into a
(presumably loose) helix for the same purpose. I've never seen RG-62
cable without the PE "string", but don't have any trouble believing that
someone might manufacture it without the "string". I also don't have
trouble believing that some auto manufacturers might use RG-62. Although
I saw a lot of auto installations in the '60s, when I moonlighted
repairing such things, I never saw RG-62. But I certainly didn't see
anywhere near every possibility, and I could have missed seeing a marking.

Roy Lewallen, W7EL

Roy Lewallen wrote:

Michael A. Terrell wrote:

I saw both types on car radio antennas, and some was clearly marked
RG-62. Both types meet the original RG62 specification, they just use
two different methods to minimize dielectric losses, like fused disk
hardline used in CATV and other applications that require low loss
cabling. Also, why would one of the Delco engineers who designed their
car radios lie about the coax they used? He was explaining the then
brand new AM/FM/8-track combo when I asked a number of questions about
the RF front end. As usual, you will continue to believe whatever you
want to.

I happened to find a piece of the automotive cable -- complete with
connector -- in my junk box, which I'm pretty sure was cut from a
replacement antenna probably purchased in the '70s. This particular
cable lacks the PE "string", but the ~#31 center conductor is crimped in
a sort of zig-zag shape to keep it in place in the hollow tube. The
aviation cable apparently has the center conductor bent into a
(presumably loose) helix for the same purpose. I've never seen RG-62
cable without the PE "string", but don't have any trouble believing that
someone might manufacture it without the "string". I also don't have
trouble believing that some auto manufacturers might use RG-62. Although
I saw a lot of auto installations in the '60s, when I moonlighted
repairing such things, I never saw RG-62. But I certainly didn't see
anywhere near every possibility, and I could have missed seeing a marking.

Roy Lewallen, W7EL

Some of the third party replacement antennas were made with military
surplus RG62, and had hand soldered motorola plugs instead of the OEM
crimped plugs. I cut up a lot of old antenna cables and stripped the
copper braid to use as solder wick by dipping it into liquid rosin. Some
had the plastic spacer for the center conductor, but most didn't. Some
weeks we replaced a half dozen car radio antennas, so I always had
plenty of copper braid at hand. years later I worked for a CATV company
repairing converters. The braid from the control cables was a little
under 1/8" when it was pulled tight and flattened by pulling it around
the blade of a screwdriver.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida