92-Ohm RG62a/u coax origins? - UK Vintage Radio Repair and Restoration Discussion Forum

Cre8anet · 14th Mar 2022, 3:55 pm

Anyone know the original application of 92Ohm cables?
...Just a bit puzzled as they appear to be impedance specific, yet some professionally made-up cables seem to have fairly standard BNCs (75Ohm?).

2000 type · 20th Mar 2022, 7:46 pm

Used for Common Aerial Working systems on RN ships.

Jon_G4MDC · 21st Mar 2022, 9:59 am

It's the impedance required to make 75Ohm quarter wave transformer splitters/couplers.

Granitehill · 21st Mar 2022, 1:46 pm

93 Ohm cable was used in vast quantitites in IBM 3270 Display System cabling. This was pretty well standard in lots of corporate IBM mainframe systems. As I remember it used standard 75 Ohm BNC connectors (the data rate was only about 2.3 Mb or so).

In general, there was something about the optimum inner/outer dimensions of coax to the effect that the lowest losses were to be found around 92 ohms, and the maximum (theoretical) power handling capability was around 37 ohms !

Jon_G4MDC · 21st Mar 2022, 3:15 pm

I'm having doubts about post#3. Might be rubbish.

Radio Wrangler · 21st Mar 2022, 4:01 pm

I'd have expected 37.5 or 150 depending on how you did it.

I'd believe the IBM one, they were up to every trick imaginable to tie people with their systems to buying their overpriced peripherals. EBCDIC VDUs anyone?

David

RogerEvans · 21st Mar 2022, 5:21 pm

It is wandering a bit off topic but EBCDIC encoding allegedly had a technical advantage over ASCII when it came to the very crude (possibly just relays) automatic processing of punched card data, which was of course IBM's origin. It was not until Unix and the Internet arrived that IBM sold ASCII based hardware and even then there were enough quirks to discourage users from mixing and matching.

I also remember the 92 ohm coax extremely well, there were literally miles of the stuff in skips at work and even hints that we would be doing them a favour if we wanted to take any home. The same thing happened a second time when 10BaseT thin ethernet was dropped in favour of Cat 5 cabling!

Roger

14th Mar 2022, 3:55 pm	#1
Cre8anet Pentode Join Date: Nov 2005 Location: Banbury, Oxfordshire, UK. Posts: 204	92-Ohm RG62a/u coax origins? Anyone know the original application of 92Ohm cables? ...Just a bit puzzled as they appear to be impedance specific, yet some professionally made-up cables seem to have fairly standard BNCs (75Ohm?). __________________ ~~~~~~May your Waves be Long~~~~~~

20th Mar 2022, 7:46 pm	#2
2000 type Tetrode Join Date: Apr 2021 Location: North Surrey, UK. Posts: 69	Re: 92-Ohm RG62a/u coax origins? Used for Common Aerial Working systems on RN ships.

21st Mar 2022, 1:46 pm	#4
Granitehill Tetrode Join Date: Mar 2019 Location: York, North Yorkshire, UK. Posts: 95	Re: 92-Ohm RG62a/u coax origins? 93 Ohm cable was used in vast quantitites in IBM 3270 Display System cabling. This was pretty well standard in lots of corporate IBM mainframe systems. As I remember it used standard 75 Ohm BNC connectors (the data rate was only about 2.3 Mb or so). In general, there was something about the optimum inner/outer dimensions of coax to the effect that the lowest losses were to be found around 92 ohms, and the maximum (theoretical) power handling capability was around 37 ohms ! __________________ John G4FDD G-QRP 431

21st Mar 2022, 3:15 pm	#5
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: 92-Ohm RG62a/u coax origins? I'm having doubts about post#3. Might be rubbish.

21st Mar 2022, 4:01 pm	#6
Radio Wrangler Moderator Join Date: Mar 2012 Location: Fife, Scotland, UK. Posts: 22,902	Re: 92-Ohm RG62a/u coax origins? I'd have expected 37.5 or 150 depending on how you did it. I'd believe the IBM one, they were up to every trick imaginable to tie people with their systems to buying their overpriced peripherals. EBCDIC VDUs anyone? David __________________ Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done

21st Mar 2022, 9:59 am	#3
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: 92-Ohm RG62a/u coax origins? It's the impedance required to make 75Ohm quarter wave transformer splitters/couplers.

21st Mar 2022, 5:21 pm	#7
RogerEvans Hexode Join Date: Oct 2014 Location: Wiltshire, UK. Posts: 382	Re: 92-Ohm RG62a/u coax origins? It is wandering a bit off topic but EBCDIC encoding allegedly had a technical advantage over ASCII when it came to the very crude (possibly just relays) automatic processing of punched card data, which was of course IBM's origin. It was not until Unix and the Internet arrived that IBM sold ASCII based hardware and even then there were enough quirks to discourage users from mixing and matching. I also remember the 92 ohm coax extremely well, there were literally miles of the stuff in skips at work and even hints that we would be doing them a favour if we wanted to take any home. The same thing happened a second time when 10BaseT thin ethernet was dropped in favour of Cat 5 cabling! Roger