But 600 miles of "baseband amplified circuits" at VF frequencies will leave you with nothing but noise.
It appears that you worked at the customer premise location and saw only the drop equipment.
And you have no idea what was in between.
Yes, most were. But not all. It was relatively easy to use a double wide channel, or use a groupband device that took up 48 KHz.
So you think an equalized audio channel over cable would, after 600 miles????
Even by the 1930's they were using phase locked oscillators (for example L carrier systems used a 64 KHz pilot to for frequency synchronization).
I worked for about 20 years on carrier systems designed in the 1930's, and never saw a single instance of a system going off frequency.
I have a book here that is definitive. It is the 1938 edition of the Bell System publication "Principals of Electricty Applied to Telephone and Telegraph Work".
A fold out chart (page unnumbered) between pages 192 and
193 shows cable characteristics for just about every common cable used at the time. The highest characteristic impedance shown (at 1000 Hz) for a non loaded cable is 19 gauge NLS at 470.1 Ohms.There is not one single cable shown as +/- 10% of 600 Ohms.
On the other hand, on page 190 there is a chart showing open wire characteristics, and more than a third of the configurations shown have an impedance within 10% of 600 Ohms.
Do see above! :-)
Repeat coils. The common designation on the device itself was "Rep. Coil".
You've never worked in the telecommunication industy?
See above for why buzz words won't get it in this conversation.
75 Ohm impedances are virtually *only* used for unbalance coaxial circuits at baseband levels for carrier systems. It is *never* used for audio, and is never used with twisted pair cables that extend past the end of rack a unit is mounted in.Obviously not.