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Old 26th Nov 2018, 12:18 am   #1
Terry_VK5TM
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Default Coax cable - When did it begin?

Back a little while ago, among a thread (which I am having trouble finding again), was a discussion on Coax cable and when it came into being.

Well, by coincidence, in a newsletter for March 2011 on this site http://www.awasa.org.za/ (go to Newsletters page and then 2011), is an article on Coax cable and who invented it.

Quote: "The first known patent granted for coaxial transmission line was a British patent in 1880 to Oliver Heaviside"

Flexible Coax as we know it didn't come into being until 1937.

Page 5 and on, makes an interesting read.
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Old 26th Nov 2018, 12:50 am   #2
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Default Re: Coax cable - When did it begin?

I think there was 'screened wire' with a braided shield around it long before flexible coax as an intentional RF transmission line came on the scene.

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Old 26th Nov 2018, 9:57 am   #3
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Default Re: Coax cable - When did it begin?

Many thanks for the link. I used to work in the communications cable industry and found much of it pertinent to my time in it during the 1970's. We used to make 174 &375 'solid' coaxial cables for the PO. By solid I mean the outer was formed by taking the required width of copper tape, using a former to turn it from flat strip into a 'butt' rounded outer with air spaced insulators inside - about the size of a shirt button on the 375 cables. Individual tubes would then be wrapped together to form the basis of the final cable before insulation was applied over the whole lot. I certainly recall 18 tube 375 cables and 4 tube 174 cables.

I was involved, in a small way, in the HF testing of a large experimental 18 tube 375 cable laid between Martlesham and the PO tower in Birmingham. Happy days going between manholes in the suburbs of Birmingham, pumping out the chamber and getting the cable jointers to connect up the test kit whilst I stayed nice and warm in the van with the homemade TDM test kit (You couldn't buy that that sort of test kit in those days). Lovely bacon sandwiches.

We also had production facilities for flexible (think TV) co-ax - Italian bit of kit. Was a real wonder to see it in action, no-one could work out how it worked! All these bobbins of copper wire flinging around some sort of inner at some horrendous speed - can't see it would be allowed these days! Think of something like a horizontal maypole.

Thanks for bringing back the memories.
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Old 26th Nov 2018, 10:32 am   #4
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Default Re: Coax cable - When did it begin?

This is an unopened 100ft length of 'Television screened feeder cable' from the 1936/37 period.

It must have been very difficult to manufacture. John.
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Old 26th Nov 2018, 6:26 pm   #5
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Default Re: Coax cable - When did it begin?

I've got a book from the mid-1930s where buried coaxial feeder is described for use in high-power transmitting-station applications. Back then it used lead as the outer sheathing, with separate insulators keeping the centre and sheath apart. Jointing was made by 'wiping' the outer to ferrules mounted on a cast-iron joint-pot with the centre conductor soldered. Very much like underground lead-sheathed power-cable of the day!
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Old 26th Nov 2018, 8:19 pm   #6
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Default Re: Coax cable - When did it begin?

I wonder when coax started to appear in domestic TV installations. Two main manufacturers of TV sets when they were first rolled out in The Netherlands were Van der Heem (Erres) and Philips. Van der Heem had a background in professional communications equipment and had great attention to detail and quality, Philips produced quality equipment as long as it didn't cost too much to make. The first Erres sets had coaxial connectors, Philips used the old balanced wiring. A few years later, Erres went back to the old system as well. In the early 1970's, coax connections were reintroduced.
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Old 28th Nov 2018, 12:22 pm   #7
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Default Re: Coax cable - When did it begin?

Maarten, was the old balanced impedance 240 Ohms?
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Old 28th Nov 2018, 12:35 pm   #8
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Default Re: Coax cable - When did it begin?

Maarten, coax was very much standard in the U.K. by the middle 1950’s.
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Old 28th Nov 2018, 1:09 pm   #9
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Default Re: Coax cable - When did it begin?

I have a Belling-Lee newsletter from circa 1952 which, while listing cable and connectors for both coax and balanced feeders, says that the balanced range will only be available until stocks are exhausted.
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Old 28th Nov 2018, 3:04 pm   #10
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Default Re: Coax cable - When did it begin?

The Wireless Set No.17 designed just prior to WWII (1938 I vaguely recall) has a coax socket for its aerial connection. I have the aerial designed for the set, and it has a coax feeder.

I also have a vague recollection that undersea telegraph cables - i.e. from the Victorian era - also had a concentric construction, like coax. Clearly they weren't "coax" as such, since the outer was designed as armouring against rupture. But I think the cable would have functioned as a coaxial transmission line all the same.

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Old 28th Nov 2018, 3:06 pm   #11
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Default Re: Coax cable - When did it begin?

As I have mentioned re the WS17, coaxial connections were well established during WWII. The Pye coax plug and socket are very well known. Presumably designed for the WS19, where I think it first appeared. It was then used all over the place, including on much radar gear.

The WS17 and R208 receiver have a different style of coax connector - no idea what its called. There were a myriad of different designs on naval and RAF kit - a mind boggling array in fact!

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Old 28th Nov 2018, 9:00 pm   #12
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Default Re: Coax cable - When did it begin?

Hi Gents, not coax as such, but screened cable where there were various screening layers in the paper insulation was, I believe, developed in the 20's to allow paper insulated cables to operate above 20KV. Prior to this development paper cables, no matter how well made, would quickly break down above this voltage.

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Old 28th Nov 2018, 9:26 pm   #13
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Default Re: Coax cable - When did it begin?

I'm sure I read somewhere once that the original trans-atlantic telephone cables were changed to co-ax types when they discovered that twisted pair types just had too much loss over the distance. Sounds like very early days but I can't recall if a particular year was mentioned.
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Old 29th Nov 2018, 12:01 am   #14
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Default Re: Coax cable - When did it begin?

I have seen some interesting variations of coaxial cable in pre -WW2 TV sets in the video sections. Also a very similar type of cable used in Tek EHT probes and some 400MHz scope probes. The idea is that a single very thin conductor sits loosely inside an insulating tube/sleeve with an air gap and it only touches the inner surface in occasional places. The thin central conductor has a very small surface area reducing the capacitance. Because it is very thin, it is often made of Nichrome to get the strength. But this kind of cable is easily damaged by careless handling.This also makes it awkward to solder and it needs crimping. It is a way to make very low capacitance per meter coax.

There are plenty of short braid screened wire link setups in 1920's radios especially in the audio sections, but I don't know if it would qualify as "coaxial cable" which would be designed as an RF transmission line with some characteristic impedance and termination for longer distance signal distribution.
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Old 29th Nov 2018, 10:40 am   #15
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Default Re: Coax cable - When did it begin?

Quote:
There are plenty of short braid screened wire link setups in 1920's radios especially in the audio sections, but I don't know if it would qualify as "coaxial cable" which would be designed as an RF transmission line with some characteristic impedance and termination for longer distance signal distribution.
Surely "coaxial" refers to two metal sections having an "axis" in common "co"? Its about the construction of the cable - not about its purpose.

So in my book a piece of "screened cable" use for microphone applications in audio work is just as much coaxial as a TV aerial feeder. That sort of cable won't be given a characteristic impedance, but might well have a capacitance per metre rating.

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Old 29th Nov 2018, 12:19 pm   #16
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Default Re: Coax cable - When did it begin?

Quote:
Originally Posted by SteveCG View Post
Maarten, was the old balanced impedance 240 Ohms?
Either 240 or 300, I'm not sure.
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Old 29th Nov 2018, 12:45 pm   #17
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Default Re: Coax cable - When did it begin?

300 ohm ribbon cable was developed in the U.S. after research and development of the
most effective cost & performance to replace the original cotton sheathed twin pitch
covered feeder, which could be brittle but also melt in higher temperature locations.
Later air-spaced, and even screened twin 300 ohm cable was available and used up
to UHF. (Source, "Television" RCA book 1946)
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Old 29th Nov 2018, 12:52 pm   #18
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Default Re: Coax cable - When did it begin?

Quote:
Originally Posted by trh01uk View Post
Surely "coaxial" refers to two metal sections having an "axis" in common "co"? Its about the construction of the cable - not about its purpose.
True, but the original post mentioned a patent for coaxial transmission line which is more about the purpose. Although Audio coaxial cable is mechanically coaxial it is not designed with a "transmission line" function in mind.
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Old 29th Nov 2018, 1:29 pm   #19
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Default Re: Coax cable - When did it begin?

Here's an advert for "CO-AX" coaxial cable from the September 1943 "Wireless World". It is the only mention of co-axial cables in the issue, and "CO-AX" seems to be used as a brand name. An internet search revealed that the company was founded in 1942 and later acquired by Radiall. Interesting that the characteristic impedances of the two cables mentioned are 70Ω and 214Ω.

In the other contemporary literature I have from the late 1930's- early 1940's, coaxial transmission lines are constructed using copper tubes and spacers. According to a booklet "The Feeders and Aerials of the Marconi-EMI Televison System" that describes the design and construction of the original transmitter aerial at Alexander Palace, it was found that the original coaxial feeder ( Marconi's standard No. 0 feeder for short waves, 78Ω ) was not satisfactory as the discontinuities introduced by the spacers, and the boxes which provided right angle bends, gave rise to unacceptable reflections, and after much experimentation, a compromise of 8 supports to the wavelength was arrived at. Presumably no coaxial cable with uniform insulation that would have avoided the discontinuity problem was available at that date. The length of feeder required was about 20 wavelengths.
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Old 29th Nov 2018, 11:08 pm   #20
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Default Re: Coax cable - When did it begin?

Regarding the balanced twin, I recall seeing American antenna stuff always referred to as 300 ohm.
However my first CTV, a NordMende 2245 (F2 chassis) back in 1970 had a balanced twin aerial input clearly marked 240 ohms.
Their earlier FM radios had balance twin for FM, I think also marked 240 ohms. Big connectors then, but smaller "DIN" types on the TV and later (1967) FM radios.
I have seen various twin cables, probably intended to be 300 ohms on far eastern sourced stuff, since there was always a USA input even if decades previously. Definitely different to some white plastic twin that was sourced in Germany in 1970.
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