50 years ago today the Bell System in the U.S. introduced dual tone multi-frequency technology which ended up replacing the rotary dial phone with the push button.
These old videos are classics!
I still remember the big dial of the rotary with the slow spin when calling my friends. The worst is when you dialed the wrong number and had to start all over. Who can't forget the old fashion bell ringing when a call came in. No music playing like today's cell phones just a serious ring. Simple times!
Here's a clip from 1963 Worlds Fair.
We hit the big time when my father installed the push button phone attached to the kitchen wall.
On a side note: Hope everyone is OK with those big storms in the mid-west yesterday, scary.
Last Sunday I built the 20 meter all mode receiver kit from Ramsey Electronics.
The HR20 is a direct conversion receiver and is built around the popular SA602 IC. This IC includes a tunable oscillator and product detector circuits which is the equivalent of seven transistors in the mixer-oscillator stages. Here is a data sheet that will educate you on the SA602 and includes more information you will ever need to know.
The audio output if fed into the LM386 IC which is the audio amplifier. I am using an earphone from an old transistor radio but this circuit would have no problem driving a small speaker with plenty of output. It is a simple build with 30 or so components that runs off a 9 volt battery and includes a case. Assembly time is rather quick, an hour or so of soldering and now on to on the alignment stage with a few broadcast stations and digital signals received so far. I really need to hook up a speaker because with the very old earphones might be creating extra hissing pitch that is unpleasant to listen to.
Also will be hooking up a frequency counter as a helper and try to get 14.060 set up. The HR20 is a fun easy kit to mess around with and includes a instruction booklet with a few modification ideas.
Will keep you posted if I decided to change things around with this receiver.