53
votes
Accepted
Amplification before tubes and transistors were invented
It wasn't.
In the early days (ca 1890) long-distance telephony was done from sound-proofed booths and often using non-standard (4-wire) telephones. New York to Chicago was the limit on range. By 1911,...
- 60.3k
40
votes
Amplification before tubes and transistors were invented
Amplification, before tube amplifiers were available, could be achieved in several ways. Some of them are:
Using a electrodynamic speaker coupled to a carbon microphone, to form a repeater.
Using the ...
- 5,317
39
votes
Accepted
Why do devices stop operating properly in extreme cold?
-4 F is -20C, which is a standard low limit for chips and electrical components. Some of that is just because it is very hard to test chips at low temperature, but there are real issues you can run ...
- 1,079
28
votes
Accepted
Phone disassembly: what's that part for?
It's a shield. It absorbs EM radiation by draining it to the electrical ground of the phone. They are used in order to meet emission specifications created by the FCC or similar authorities, or to ...
- 48.4k
28
votes
Accepted
How does the telephone's keypad work?
There is a conductive pad on the bottom side of the button that "shorts" out the spiral. Usually dark grey since it is carbon based.
The spiral just give you a higher probability that the pad will ...
- 46.5k
28
votes
How were four wires replaced with two wires in early telephones?
Remember that the telephone was invented over 30 years before the triode vacuum tube, and over 70 years before the transistor. Changing, combining, and subtracting audio had to be done with resistors,...
- 18.2k
22
votes
Amplification before tubes and transistors were invented
The funnel you're supposed to yell into is actually a horn:
Horns are acoustic transformers, they are usually used the other way around: a high-pressure transducer ("compression driver") is mounted ...
- 72k
22
votes
Can lightning strike into the phone line damage electronics in the house through the ADSL modem?
There are many 'entry points' to your house for electrical disturbances, once lightning has struck close by, and the most important of these is the mains. A nearby strike will lift the ground ...
- 162k
20
votes
Why do devices stop operating properly in extreme cold?
For most of these devices it's the display...
LCDs don't like the cold.
Typically, standard LCD character and graphics modules provide a temperature range of 0°C to +50°C. However, several display ...
- 46.5k
19
votes
Why do push button telephones use dual-tone for signalling?
If you used single tones instead of dual tones, you'd need 16 of them instead of only 8 as in the DTMF system.
Given that they have to be spaced far enough apart for reliable detection, and that you ...
- 69.1k
18
votes
Amplification before tubes and transistors were invented
The pre-vacuum-tube telephone system used exactly the carbon-granule microphone as the amplifier. What Bell invented was the use of essentially the same device as speaker and microphone. Now we call ...
- 321
16
votes
Why do devices stop operating properly in extreme cold?
Batteries dislike cold.
Generally all batteries lose capacity and current in the very cold. (However, using them often warms them up.). Lithiums have a particular problem with being charged in the ...
13
votes
What do you call the yellow and black conductors in domestic telephone wire?
This is going to be boring but from what multiple sources are saying, they're called, wait for it.... Tip2 and Ring2. The green and red are Tip1 and Ring1.
The jack you speak of is RJ14 (vs the RJ11 ...
- 12.8k
11
votes
Why do PBX systems use -48 V?
Electrically it makes no difference if the ground is positive or negative the components will be connected accordingly. However in the early discovery days when electric trams and telephone cables ...
- 111
11
votes
Disable ring on land line phones
I'm taking a wild-assed-guess here, but I suspect that the circuit consists of a simple Metal-Oxide Varistor (MOV) with the appropriate voltage rating in series with a largish capacitor, all connected ...
- 23.6k
9
votes
Amplification before tubes and transistors were invented
If you could call it amplification, it was done in the carbon microphone into which you speak. A voltage was applied across the carbon element of the microphone. Sound waves altered the resistance of ...
- 485
9
votes
Why do devices stop operating properly in extreme cold?
Crystal oscillators may not start up; or the crystal resonant frequency, which has a temperature coefficient, may be outside the guaranteed Automatic Frequency Control (afc) range, needed to ensure ...
- 33.8k
9
votes
Accepted
How was the first overseas phone call possible back in 1927?
The system you're referring to was described briefly in the Bell System Technical Journal in 1935. Most of the article is about measuring the advantages of the (then brand-new) "single-sideband ...
- 6,990
9
votes
How were four wires replaced with two wires in early telephones?
It is done with a circuit that sends the microphone signal to wires, but removes your own microphone signal from the wire signal before sending it to the speaker, so that only thing that can be heard ...
- 137k
8
votes
Why do push button telephones use dual-tone for signalling?
It is because phone systems were designed with in-band signalling due to technical limitations at the time.
The signaling worked over the existing telephone infrastructure that previously was ...
- 72.8k
8
votes
CAT5 for telephony
A CAT5 cable has 4 twisted pairs. You will want to use 1 pair of wires per phone line. The standard arrangement is the blue pair is the first phone line.
Assuming the wiring your connecting to is the ...
- 237
7
votes
When a AM radio wave reaches the antenna does the signal need to be in a closed circuit to be amplified?
Some antennas only appear to have one connection. In that case, the ground, or ground plane, is the other implied connection. In the case of something like a long wire out a window, the other ...
- 312k
7
votes
Why telephone dc voltage drops to about 8 volts?
The telephone handset impedance is about \$600\:\Omega\$. There is also any output impedance at the central office (not uncommonly \$1\:\textrm{k}\Omega\$), plus a LOT of wiring going from the central ...
- 77.4k
Only top scored, non community-wiki answers of a minimum length are eligible