The first thing that boggled my mind is that the face plate says the output is 52 ohms ?! Yes 52 not 50 ! So you need 52ohms coaxial cables and plug that into a 52 ohm load/scope, if that even exists ?! I guess there must exist 52/50 ohms adapters ?! Still, why not make the oput 50ohms to begin with ?! how pervert is it to make a 52 ohms output ?! WHY ?!
Is it a " thing " to be 52 ohms in the test and measurements arena maybe, at that time anyway ? What's so special about 52 ohms that you can't do with traditional 50 ohms ? I am genuinely curious, I am sure I will learn something...
Back in the day, the "official " impedance for coax of that type was 52 ohms.
Over time, it became "normalised" to 50 ohms, which is amusing, as 52 ohms was, itself, a "normalisation" of 51.5 ohms.
Marconi, in the UK, still used 51.5 ohms as their standard.
Thus, it came to pass, that the twin 10kW TV "Vision" transmitters (& their associated "Sound" Tx) installed around 1959 at ABW2 were to that standard.
TV transmitters of that era "grid modulated" the final RF PA stage, producing a "double sideband, full carrier " (AM) signal.
The standard was "Vestigial sideband" (VSB), so most of the lower sideband had to be suppressed.
Much of this could be achieved with the PA tuning, but to get the result "in spec", an RF filter was needed ---A bloody big one!
To this end, "filterplexers" were used, which, in addition to filtering the LSB, also were used to combine the Sound & Vision RF signals.
The resultant signals were then fed to a "combining unit", so two of these transmitter combinations could in their turn, be combined to send 20kW of Vision & 4kW of Sound signals "up the spout".
All of this stuff required a lot of "plumbing", consisting of coax made up of large diameter aluminium tubing, with smaller dia copper tubing suspended inside it by Teflon spacers----all 51.5 ohm!
The 1970s rolled around, & the decision was made to modify the existing transmission equipment for PAL colour, so along with a lot of other stuff, they also decided to replace the "filterplexers", combining units & associated plumbing with new units which could better meet the tightened specs required.
All good, but the new stuff, supplied by AWA, was all for 50 ohms!
The transmitters, the coax up to the antennas, & various other bits were not going to be changed, staying at 51.5 ohms, so AWA supplied "at considerable expense" a bunch of 1/4 wavelength "matching sections" of 50.7445 ohms!
These were provided, by the simple expedient of turning down the centre conductor of normal 50 ohm coax to a smaller diameter.
"A nice little earner" for AWA, but I bet the machinist didn't get a bonus for his contribution!