Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

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

It was RG62 93 ohm coax. The connectors were called "Motorola"
plugs.
--
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

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

Those connectors are still in use today in UK & Europe at least. A UK
supplier is Maplin electronics.

www.maplin.co.uk part no HHH12N

Reagrds
Jeff

Question about auto antenna cable and connectors
 

Thanks for the lead. I see them on their web site.
Ronnie

"Jeff" wrote in message ...
Those connectors are still in use today in UK & Europe at least. A UK
supplier is Maplin electronics.

www.maplin.co.uk part no HHH12N

Reagrds
Jeff

Question about auto antenna cable and connectors
 

Ronnie wrote:
Thanks for the lead. I see them on their web site.
Ronnie

"Jeff" wrote in message ...

Those connectors are still in use today in UK & Europe at least. A UK
supplier is Maplin electronics.

www.maplin.co.uk part no HHH12N

Reagrds
Jeff




Jeff and Ronnie;

That type of connector is known as a "Motorola Connector". Developed by
Motorola for their automobile radios.

Dave N

Question about auto antenna cable and connectors
 

We purchased a new 5th wheel trailer a month ago and had to replace the
stereo unit. Was I surprised when I pull the old one. It used the old
Motorola auto antenna connector and cable to the antenna on the RV
roof. So, I guess the antennas, cable and connectors are still being
made and used today.

Paul in Redmond, OR

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

- 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

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

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

Question about auto antenna cable and connectors
 

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