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,...
- 60.8k
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 ...
- 5,367
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
36
votes
Accepted
How were four wires replaced with two wires in early telephones?
How was this possible? Wouldn't the current from microphone affect
speaker on the same side?
The modern telephone is wired in a Wheatstone bridge arrangement like this: -
So, if you ensure that the ...
- 466k
29
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,...
- 22k
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 ...
- 46.9k
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 ...
- 80.3k
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 ...
- 171k
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 ...
- 46.9k
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 ...
- 73k
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 ...
15
votes
Amplification before tubes and transistors were invented
Telephones are older than vacuum tubes and of course transistors. How
was signal amplification done?
I remember when I was a kid you could buy a plastic handset that connected to another plastic ...
- 466k
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 ...
- 12.9k
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
Accepted
When a AM radio wave reaches the antenna does the signal need to be in a closed circuit to be amplified?
When a AM radio wave reaches the antenna does the signal need to be in
a closed circuit to be amplified?
Yes, and believe it or not there is a closed circuit. A simple monopole antenna uses ground ...
- 466k
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 ...
- 24k
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 ...
- 34.6k
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 ...
- 7,948
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 ...
- 164k
9
votes
How does a UK analogue telephone detect that the caller has hung up (disconnected)?
I need the UK protocol
Wiki - Disconnect tone gives you details for the UK: -
A disconnect tone in telephony is a tone provided to the remaining
party to a call after the remote party hangs up. ...
- 466k
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 ...
- 73.3k
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
8
votes
What do you call the yellow and black conductors in domestic telephone wire?
UK telephone answer
If you look at the old UK telecoms specifications (BS6305 and BS6317) the main 2 wires were called A and B with "B" being pin 2 and "A" being pin 5 on the 6-pin ...
- 466k
8
votes
How is message waiting conveyed to home POTS phone
In addition to the dial tone stutter mentioned in Spehro Pefhany's answer, FSK-based ADSI (i.e. the same channel used for caller ID on POTS lines) also provides a message-waiting indicator that can ...
- 20.3k
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 ...
- 314k
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 ...
- 78.4k
Only top scored, non community-wiki answers of a minimum length are eligible