usual introductions, I started to ask all those questions
about loops, tandems, etc. Jimmy was incredibly excited that
I know how to build electronic things and that I had built
a transmitter. Jimmy said, "can you build an MF'er?",
I said "What?" and asked Jimmy to explain what it
was. An MF'er, short for Multi-Frequency, was nothing more
than a tone device that generates 6 tones, which were 700,
900, 1100, 1300, 1500, and 1700 Hz.
The Phone company used these crude devices to switch long
distance calls by passing these tones over the same lines
we use when we talk over them. This is supposed to save the
phone company millions of dollars in equipment.
Jimmy, excited with the possibility that I would build such
a device, jumped up and said "Let me demonstrate!"
He asked me who I wanted to call, anywhere in the USA. I gave
him the number. He said, "First, I'll dial a toll free
800 number". So he dialed the number on a "Speeded
up rotary phone" he called a "Zip phone". I
was amazed at how fast the rotary dial would return and yet
have the equipment register the number that quickly.
Just as the
800 number was ringing, Jimmy hit the "E" key, one
octave above middle C, and the ringing would stop, and I would
hear a chirp sound and an empty line with a very soft hiss
sound. This is 2600 Hz.
After that, jimmy would play chord
pairs of notes that sounded exactly what I used to hear when
making long distant calls. I heard a ring, and my friend answered.
WOW! It worked. It blew me away... I started asking question
after question, and Jimmy was only too eager to answer them.
Essentially, it works like this. When a long distance trunk
line is idle, it sends 2600 Hz tone to the other end. Both
sides send this 2600 Hz tone to each other. So, when a line
is idle, it uses more electricity... Hmmm!! I can remember
later on, during court arguments where the district attorney
argued that my romping through the phone system was using
more electricity, thus costing them more money. Yea, RIGHT!
Anyway, after playing around with Jimmy's organ, I headed
home and dug out my trusty parts bins, found my slide rule
(Calculators weren't invented then), and calculated the parts
values I would need for each of the frequencies.
In about 45 minutes, I had all 6 of the oscillators connected
to an op-amp to the phone line through a transformer. I only
had a single button for each tone initially, because I didn't
have enough diodes to switch two at a time. It took practice,
but I managed to MF numbers and thus was the start of my exploration
of the phone system.