What Are Rotary Dial Phones and How Do They Work?

Interesting Engineering ^ | 6/5/21 | Christopher McFadden

[DallasBiff]

The rotary dial phone was once the be all and end all of the telephones. Like the cellphone of today, everybody had one, and they ruled domestic communications for decades.

But that all changed in the 1980s when they were supplanted by a new upstart, push-button telephones. Their days were numbered (pun intended).

Many born after the 1990s have likely never seen one, which is a shame. But for those who do remember, join us as we take a trip back in time in remembrance of this glorious piece of telecommunications history.

[Harmless Teddy Bear]

There was a handle.

Right under the receiver.

You slid your fingers in there and used your thumb as a guide. A couple of swings to get the momentum going and you could really put a dent in something.

[old-ager]

I did not know that! Wish I could go back and play with it.

I think there ws a secret number that would tell you the phone number you were calling from, and another one that would phone you back as a test.

I’ve wondered if there were any filters on pay phones to stop someone from playing back the coin chimes from a tape.

[Jamestown1630]

The DC number is different from the old days, but cool to know you can still phone-up the time.

[cymbeline]

“This just one of the things about the old analog phone system that were very clever. “

You want “clever”, look into the original color TV design. Done initially with vacuum tubes (not thousands of transistors), and the color signal would work with the old black and white TVs. And the sets were manufactured at consumer prices.

And the picture tube was very complex with three guns that shot three beams through a mask to illuminate thousands of red, green and blue phosphors.

[TangoLimaSierra]

She had a 3 digit number

Was there a 'BR' in front of the numbers?

[Jamestown1630]

69. Now, I think it’s *69

[null and void]

Rings were caused by 40 volts DC flowing down that circuit. That voltage could knock you on your butt.

100V DC pulsed at 20 Hz.

Plenty enough to get your full undivided attention...

[old-ager]

Combination transducer and amplifier before there was amplification! Need higher level? Turn up the voltage!

[MeanWestTexan]

The phone in the bunk house on our ranch is a rotary that used to be a party line, but no one else shares the line. We keep it bc the cell service can’t reach. Property line is literally over the horizon.

You can dial it by clicking the “hang up” switch (so 7 quick taps for 7, for example), which is, btw, all a rotary phone is doing.

[Jamestown1630]

Is this why people were wary of being on the phone during thunderstorms?

[Captain Peter Blood]

Theirs and also stifling competition. If ATT has not been broken up Cell phone technology would have been another 20 years down the road. ATT was a controlling public Monopoly , look up the court case. When ATT was finally broken up, there was an explosion in technology advancement especially in Cell Phones.

[Steely Tom]

You want “clever”, look into the original color TV design. Done initially with vacuum tubes (not thousands of transistors), and the color signal would work with the old black and white TVs. And the sets were manufactured at consumer prices.

True. No argument there.

TVs were one of the first places where phase-locked loops (PLLs) were used in a consumer product.

Color TV depended on PLL technology even more.

FM Stereo wouldn't have been possible without it.

The PLL was one of the great innovations of electronics, incredibly useful and versatile. A case where the whole was much greater than the sum of its parts, the added ingredient being cleverness.

[old-ager]

> 20 Hz

With, what, 400 Hz on top of that? That’s what created the ring sound heard by the caller. When I first heard the sound when farting around on an incoming line, I realized that the audio was connected to the caller while ringing and you could send audio back without picking up the line.

[Myrddin]

I was in a 12 week course at the Bell System Center for Technical Excellence in Lisle, IL in 1980. We were treated to previews of unreleased technology. One of the stranger items was a D to A audio transducer. The phone was on a digital line and the earpiece had a set of semi-circular elements whose size represented the weight of a bit in the digital data. It was a simple electro-mechanical device. Fidelity was acceptable. Not as spiffy as the integrated circuits with u-law or a-law DtoA converters used now. The switch room had an old #1 ESS with core memory and ferrite sheet memory. All discrete components. Equipment frames were 6 feet tall and 30 ft long. Loading the call store was a 3 week operation. The "code" arrived on aluminum plates with ferro-magnetic squares representing bits of the 43 bit call processor. A milk carton size box held about 30 plates. It held a rack that could hang on the "card reader" to read the data into the core call store. Really primitive. The 30 MB hard disk had two surfaces with fixed head disks. It was spun with a washing machine motor with belts.

At the time I took the course, my duties at work included removal of analog O/ON carrier systems and installation of T1/T1C repeater bays and D4 channel banks.

[MeanWestTexan]

Assuming you were stupid and didn’t have a lightening arrestor, yes.

[null and void]

ding, ding-ding, bong
nickel, dime, quarter

[gundog]

Harder than a hippie’s head....

[Jamestown1630]

I have no idea what we had. I just know that some people were afraid in thunderstorms. I don’t recall ever being advised about it.

[Jamestown1630]

Never mind - 69 was how you found the number that called YOU last.

[null and void]

See gnarledmaw’s post #63...