Sunday, October 8, 2017

TV and Radio Dials ("Don't touch that dial")

I subscribe to the daily Chicago Tribune and on October 3 the bag included a copy of the Sun-Times as an advertisement. So I had a chance to read the Garfield comic that had three frames. The first frame shows Garfield watching a flat-screen TV. The TV had the narration of DON'T TOUCH THAT DIAL. The second frame had Garfield thinking OKAY, I WON'T. The third frame had Garfield breaking the fourth wall and thinking AND WHAT'S A DIAL?

I have already discussed a dial phone. Garfield's comic reminded me that a tuning dial is history for both radios and TVs.

TV Tuning Dial


My first TVs, including my first color TV --- a 19-in RCA XL100 --- had dials for selecting the channel.

Photo by Bmuscotty88, CC BY-SA
I had to hunt on the web for a while to find a photo of a TV that was old enough to have a dial and with enough resolution that you could see the numbers on the dial.
Digitally zoomed
When I was a kid, our TVs had just the top dial without the U. That is, the TV could receive just the VHF (Very High Frequency) channles 2-13. To change channels, you had to get up off your seat, walk across the room to the TV, and turn the dial to the new number. When you turned the dial, it would "click" (actually, "clunk" is probably more accurate) at each number. And you had to turn it rather strongly to get it to move to the next number. When I took the cover off a TV, I noticed that what is on the backside of that dial was rather complicated. It was several inches deep consisting of several banks of selector switches. It always blew my mind trying to figure out how they were manufactured in the factory. The newer model shown in the photo supports UHF (Ultra High Frequency) channels as well. If my memory is accurate, that dial turned smoothly.

The fact that we did not have a remote and we could not channel surf was not an issue because we had only three channels --- ABC, CBS, and NBC. Since there was just one TV in the house and just three channels to choose from, who was going to watch what was planned out long before the TV was turned on.

Why just three networks for so many decades? Sending video signals across the country was difficult. Fortunately, using underground coax cables across the country was invented about the time that TV was invented. One was laid across my grandfather's farm in northeast Indiana.
  • 1936 — AT&T installs experimental coaxial telephone and television cable between New York and Philadelphia, with automatic booster stations every ten miles. Completed in December, it can transmit 240 telephone calls simultaneously.
  • 1941 — First commercial use in USA by AT&T, between Minneapolis, Minnesota and Stevens Point, Wisconsin. L1 system with capacity of one TV channel or 480 telephone circuits.
  • 1949 — On January 11, eight stations on the US East Coast and seven Midwestern stations are linked via a long-distance coaxial cable.
[Wikipedia]
Microwaves and satellites had to be invented to afford enough channels to make channel surfing a meaningful activity. Then when we were forced to switch to digitial channels, channel surfing became a joke because it took so long for each channel to buffer up and display an image. I notice now that they at least quickly display the name of the channel. With the advent of fiber optic transmission making streaming possible, channel surfing became even more silly. In fact, some would argue that the TV is obsolete.

I had read that the mechanical turner was the weak spot in the XL100 TVs. But that turned out to be OK because soon after I bought my color TV, I bought my first VCR --- a JVC for $800. (The last VCR I bought new was also a JVC, but it cost $30.) So the turner on the TV set on channel 3 because I used the remote of the VCR for channel selection. (Every once and a while I would click it back and forth a few channels to wipe any corrosion of the contacts.) I finally threw that 19" color TV away after a couple of decades, not because it quit working, but because I wanted a bigger TV.

Radio Tuning Dial


Radios had a knob that turned the shaft of a variable capacitor. There would be a cord that wrapped around the shaft of the little tuning knob and then the cord went around a big pulley on the variable capacity. It would take many turns of the knob to go from one end of the dial to the other. And you had to remember the numbers of the AM stations that you liked. (There was no FM radio when I was a kid.) To this day, I remember from the 1960s that WOWO (Fort Wayne, IN) was 1190 and WLS (Chicago) was 890. I no longer remember the frequency for WCFL, the other top-hits radio station.

Pinterest
I don't know what the lower scale in the photo was. When I was looking at pictures of older radios, I noticed that most of them had both scales.

Photo
A variable capacitor has two banks of metal plates. The lower bank was fastened to the frame and was stationary. The other bank of plates was attached to the shaft. In this case, when you turned the shaft clockwise, you would rotate the plates out of the stator plates, which decreased the adjacent surface area and decreased the capacitance. Likewise, turning the shaft counterclockwise put more area of the rotor plates next to the stator plates and increased the capacitance.
By the time radios were being installed in cars, the dial had been replaced by a slider.
Nathan Gryszowka
For a slider, the cord between the knob and the capacitor pulley was run across the top of the scale and the needle was attached to the cord.

Photo from CollectorNet
The first purchase I made with my own money (lawn mowing and babysitting) was a portable transistor radio. I added a blue rectangle on the photo to highlight the "teeth" that stuck out on the side of the radio. These were on the tuning dial. This dial was directly attached to the variable capacitor shaft. There was no cord to "gear down" the number of turns between the knob and the capacitor shaft. It required careful thumb movement to tune in a station.

Update: A Flickr photo of a 1946 Farnsworth vacuum tube radio with a slide dial. Of course, back then it would be just AM, there is no FM scale. (Note the "Vintage Tech" album.)
Marie Dawson shared
Bob Garrett commented on Marie's share
If I remember correctly, after they played the anthem, they showed a test pattern for a while before they turned off the signal and the set would show static. You would also get static if you set the dial to a channel that was not used. I'm sure they also showed a test pattern before their first show so that you would know you were tuned in to an active channel. But I don't remember that because I was never up that early.

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