- 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