Card 6: Milliwatt Test and FM radio line. DSCN0470

Milliwatt Tests were (and still are, these things still can be found and called in the modern phone network), used for transmission level testing.
The idea is to have a known frequency being transmitted at a known level.
These are typically 1000 cycles at 0 db. (they had to later change it to 1004 cycles because of some weird aliasing that happens when you sample
at 8 kHz on a T1 channel)... So a typical milliwatt test is a continuous 1 kHz
sine wave sent out at 0 db, and interrupted for 1.25 seconds every 10 seconds. The other line on card 6 is an FM radio line. Milliwatt is 681, FM
radio is 533. Note that 681 can also be dialed as 3381, and 533 can also be dialed as 3233. That is in the dial-plan here. 5XX is 32XX, and 6XX is 33XX.
That oddity came about when the switch was expanded from the original 100 lines, by the addition of another 100 lines. By that time I had gotten so used to those old 5XX and 6XX numbers and they are printed on dial centers
for lots of phones, I opted to keep them in the system, and then simply
add duplicates in on 32XX and 33XX. Doing so made the transition
to 200 lines very easy and very straightforward because the 3rd connector
shelf added has 34XX numbers in it. The 34XX numbers have no 3-digit
equivalent. So the dialplan ends up having uniformity of 32XX, 33XX and 34XX. This is why sometimes you will see me dialing 3 digits, and other times 4 digits because of this overlay of old and new dialplans.