Broadcasting starts with a microphone. The best microphones of
all time were the RCA ribbon microphones, the most famous being the model
44BX and later the 77DX. Singers such as Bing Crosby and Mario Lanza
sang into such microphones which gave their voices that deep rich resonant
sound so characteristic of the early recordings.
The RCA 44-BX microphone (1930's -1940's)
The RCA 77-DX microphone (1940's - 1960's)
Here is a picture of the microphone I actually have, an RCA 77-DX:
Next, all the microphones and turntables or CD players at the station
are fed into a mixer, where each one can be turned off or on, or the volumes
of each adjusted, by the program engineer. Here is an old RCA mixer
console that has 4 channels:
Here is the RCA mixer I actually have, an RCA BC-5B:
and a view inside it:
The sounds going into a microphone vary in intensity, depending on the
person's voice, distance to mic., and orchestra instruments being played.
The range of the softest to loudest sounds the microphone picks up is much
too great to be transmitted onto vinyl recordings or over the airwaves
on radio...and vary much too quickly for a program engineer to constantly
be fiddling with...so an automatic volume controller is needed: The
So the signal, after it is picked up by the microphone and mixed with other mics in the mixer, goes into a compressor.
This is an old Gates company compressor...it takes sounds which vary in volume by 10x and compresses them to be only 3x different.....100x difference in intensity of sounds would be compressed to only 30x difference, etc. This is a big help in making more even the sounds of vastly different loudness coming into the microphone.
Now that the sounds are more or less evened out, there is still the
issue of PEAK loudness versus AVERAGE loudness...in normal human speech,
the peak loudness as seen on an oscilloscope display of the voice wave
can be 3x that of the AVERAGE loudness. Even though our ears respond
to average loudness to tell us how loud a sound is, electronic apparatus
must still handle the peaks without overloading or distorting...and in
the case of a transmitter....there is a maximum signal level it can handle
before it overloads and causes severe intereference to neighbouring frequencies
or channels...so the peaks must be limited somehow. Another advantage
of deliberately squashing the peaks while riding up the average through
a piece of equipment is PERCEIVED LOUDNESS - it goes up. Rock and
roll radio stations use this trick to make their signals sound loud, go
farther, even though they haven't changed their transmit power or antennas.
Early Beatles recordings used tremendous peak squashing to create a sound
that had almost the same loudness all the time through the whole recorded
song. The device that does this is a PEAK LIMITER... so our
signal then goes into a LIMITER. These are pictures of the actual
Gates Co. Limiter I have:
and a view inside it:
This limiter is very effective (peaks can be squashed as much as 2.5 times down from their original height, without changing the average sound level, the result being the new signal seems now 2.5 times louder without overloading the amplifiers in the transmitter.
Here is a picture of my vintage studio:
Next, we need a transmitter.....a transmitter generates a carrier wave
at high radio frequency, such as 1050 kilocycles = 1,050,000 waves per
second such as on radio station CHUM-AM in Toronto, or even higher, such
as 98.1 megacycles = 98,100,000 waves per second such as from radio station
CHFI-FM in Toronto. The carrier wave is modulated or changed in accordance
with the voice or music signal from the output of the limiter to produce
the final radio waves that are send out for broadcasting through the air.
A small 1000-watt radio transmitter...it generates the carrier wave frequency of the radio waves, and also has a modulator built in into which the voice or music audio signal is fed in.
A small 1000-watt radio station could have the studio equipment and
transmitter in the same room...such as this really neat one in California.
A 50,000 watt radio transmitter would be much, much larger of course, and occupy several rooms with equipment. Usually the transmitter is in a separate building because of the noise and necessary cooling equipment.
An antenna completes the radio station...the structure that radiates
the waves into space, for far away radio receivers to pick up.
Well, this is the stuff that I'd stay up all night for as a kid, and
take out a hidden book I had stuffed between mattresses, and turn on a
flashlight and read in the middle of the night....much to the chagrin of
my parents. But I sure learned a lot and it was such fun! There
is something almost magical about bits of iron, copper, glass, and rubber
put together the right way that can send your voice or music or pictures
thousands of miles away through space: radio and television.
Today, everyone is into computers and the internet...but that isn't nearly
as magical and fascinating as radio. Take a closer look at your radio,
visit a radio station, and re-learn the fascination of radio that enthralled
thousands of listeners in the 1920's 30's and 40's and which ushered in
the 20th century of high technology and wireless communications.
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