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PMG Telecom Radio Laboratory Books and Calibration Box Information

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The1:
i guess it would be good to have them up somewhere searchable hence why i put them here and other places. I guess there's not really anywhere for the physical books to go? The Telstra Museum, NLA and State library's dont want them as they are internal books not published.

The1:
I have 3 of these box's now has anyone used them? I am guessing there calibration or used to test inline Equipment? this one's a different one than the other one above.

vk6zgo:

--- Quote from: The1 on June 20, 2021, 07:58:48 am ---I have 3 of these box's now has anyone used them? I am guessing there calibration or used to test inline Equipment? this one's a different one than the other one above.

--- End quote ---

It looks like a 600 \$\Omega\$ to 200 \$\Omega\$ matching pad.

Unlike the ones normally available for general use in telephony, or those made up with discrete resistors by Techs, the impedance matching will be very accurate, with the resistor values closely following those spat out by the design formulae.

Kerlin:
From my experience that was not used for calibration.
Equipment for everyday use was made to that kind of standard, that's how things were done.
Calibration gear would have been of a much higher standard.
It was probably used in conjunction with a transmission measuring set (TMS) for terminating a line into the correct impedance.
The TMS used was the AWA A220 and there was also another model of the same thing but was a longer shorter format.
I can recall using a box similar to that when doing what was called a "line up" (level check and adjustment) on long line carrier systems for telex use.

The resistances provided by it does match with the impedance of the various types of communications lines, however it is missing 135 ohms for twisted pair cables but 200 would be close enough as practical line impedances do vary.

I had a great laugh at a linesman who called me when I was working on a test desk, he asked me to check a particular pair in a cable because he thought it had a "partial short".
So he would have thought it was for putting partial shorts on lines.
I should have asked him how many ohms a standard partial short was - Hahaha

The1:
thankyou for the reply, most interesting!

I will use these to check my meters regardless i think as they all read the same, handy boxs for extra resistance checking.

I had not looked on the bottom but one has stamped May 1951.

They all also have numbers on them, the 600ohms ones are no12 and the dual 600/200 ohms are 14 so perhaps there are many others out there with different configurations.

The 600/200ohms one also has written on it 10db loss @ 1kc/s So used with transmission equipment sounds right, also being that they are from the PMG Radio Laboratory.

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