Coax cable - When did it begin?

[Terry_VK5TM]

I remember seeing the shielded cables in older gear but would you call that coax as we know it today? it appears modern suppliers still call it shielded cable.

By coax I mean specifically the flexible controlled impedance stuff for RF that at this stage seems to have arrived in/around 1936/37 and discounting the solid/hard tube type that was around before then.

John's post #4 with the picture of the 'Television screened feeder cable' must be some of the very first coax of the modern style.

As the grey cells rapidly progress towards their use by date, I'm finding what everybody has posted very interesting and thank you all for it, it brings back long lost fleeting memories of all sorts of things.

[Maarten]

Originally Posted by MotorBikeLes

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.
Les.

I'm a bit suprised that that set still had a balanced input. As far as I remember, German sets from that era already had coax inputs. Could this have been something for export (UK) sets? Or maybe I'm confused because of the F2 designation. Wouldn't that have been from the late 1970's?

[MotorBikeLes]

Maarten, Yes, definitely 240 ohm. I wrote to BBC Technical asking advice, and received a sketch of a 75 ohm feeder with a loop (lambda/2 I think)to present the 240 ohm input to the set. I still have the sketch. 1969/70, I was trying to buy an empty cottage, but the deal fell through, so I bought the TV as a substitute. Later the cottage was re-offered, so I had both.
The F1 chassis (I think) was 19" and 25" 90 degree CRTs.
The F2 was 22" and 26" (mine was 22"), with PL509, GY501 and PD500 at the hot end.
The F3 was hybrid with tripler, 110 degree CRT.
The F4 was the first all transistor, with many more Fx versions following.
I still have most of the manuals and catalogues of the period. From 1980, I started buying NM F4 CTVs and many other Grundig CTVs and built a little one man business.
We had a local "one man band" importer of NM and some other German radios and TVs in the next town, and he would mostly buy end of line stuff, but would also get stuff to order, such as my 2245..
Les.

[trh01uk]

Originally Posted by Terry_VK5TM

I remember seeing the shielded cables in older gear but would you call that coax as we know it today? it appears modern suppliers still call it shielded cable.

By coax I mean specifically the flexible controlled impedance stuff for RF that at this stage seems to have arrived in/around 1936/37 and discounting the solid/hard tube type that was around before then.

John's post #4 with the picture of the 'Television screened feeder cable' must be some of the very first coax of the modern style.

As the grey cells rapidly progress towards their use by date, I'm finding what everybody has posted very interesting and thank you all for it, it brings back long lost fleeting memories of all sorts of things.

Terry,

as I pointed out before "coax" only refers to two wires with a common axis. And that's true whether its called "screened cable" or anything similar. Its a matter of simple physics that if you take two such cables - arranged in what we all refer to as "coax" - it will have a specific impedance. And that impedance is defined by the well known equation as described (for instance) on this webpage: https://radio-electronics.com/info//...-impedance.php

The only factors defining that impedance are the diameter of the inner and outer conductors and the relative permittivity of the dielectric.

Of course some cables with this kind of construction may well not have those 3 factors well controlled. In which case the impedance is going to vary, and its RF characteristics won't be well controlled either.

So I suggest "coax" applies to all twin core concentric cables - whether or not the manufacturer chooses to specify an impedance and perhaps a loss factor at a specific frequency (typically dB/m loss at a specific frequency).

So I would conclude that "coax" was around long before anyone was accessing frequencies that were helped by that specific style of cable construction, i.e. sometime in the 1930s.


Richard

[Maarten]

Originally Posted by MotorBikeLes

Maarten, Yes, definitely 240 ohm. I wrote to BBC Technical asking advice, and received a sketch of a 75 ohm feeder with a loop (lambda/2 I think)to present the 240 ohm input to the set. I still have the sketch. 1969/70, I was trying to buy an empty cottage, but the deal fell through, so I bought the TV as a substitute. Later the cottage was re-offered, so I had both.

Sound like you had a good deal

With regards to the F numbering, my memory must have been off. I think I confused F and ICC numbers... In the late 1970's, somewhere in the middle of the SK3 chassis family (I should search for the details, possibly F7 or F8), Nordmende started using the Thomson ICC chassis, but still numbered most Thomson chassis in the F series for some years after that.

[MotorBikeLes]

Maarten, whilst no real quantity importing of NM stuff here, the F6 portable WAS imported in biggish quantity as a Ferguson (3538) It preceded the big takeover/merger under Thompson.
Back in about 1989, I was working for a Pioneer dealer (Audio only for sales purposes) but a customer turned up with a Pioneer CTV with "No Sound". When I looked inside, I immediately decided it was a NM chassis. Typical panel part numbers of the 123.456 style. I had to ring Pioneer Tech for help. It was my first encounter with a set where one sets "Segments" of an on-screen display.Reset from 5.5 to 6.0 sound carrier. It probably came from Germany, but I never found out.
Les.

[Richard_FM]

Slighty OT but similar to the above was the German market Philips TV my old girlfriend's Mum had brought over from Germany after Gran's house was cleared.

It had a habit of reverting to system B/G when it was unplugged for a more than a few days, & every time we visited it was up to me to sort it out.

It just needed a search through the on-screen menu to set it to system I, I think I just to set the country to UK & it would automatically switch the sound accordingly.

Apart from this it was hard to tell it wasn't UK spec apart from a short lead on the back for the VHF aerial, which was a balanced pair terminated with a 75 Ohm connector.