Voice Modulation: Difference between revisions
(New page: ;Correlative terms that may appear in TIGHAR resources : phone : radiotelephone, radiotelephony : voice transmission {| border=1 cellpadding=5 |+'''Classification of transmission modes'''...) |
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== Related articles == | == Related articles == | ||
* [[Radio equipment on NR16020]] | * [[Radio equipment on NR16020]] | ||
* [[ | * [[Frequency, wavelength, and antenna tuning]] | ||
== References == | == References == | ||
Revision as of 20:22, 6 October 2009
- Correlative terms that may appear in TIGHAR resources
- phone
- radiotelephone, radiotelephony
- voice transmission
| A1 | Continuous wave (CW) |
| A2 | Modulated continuous wave (MCW) |
| A3 | Voice modulation, radiotelephone |
To transmit voice over the radio, the audio wave pattern picked up by a microphone is superimposed on the transmitter's carrier wave; the audio wave modulates (controls the shape of) the radio wave.
To equip a transmitter to send voice, one needs at least a microphone and a modulator circuit. In the Radio equipment on NR16020, the audio waveform picked up by the microphone was amplified in the modulator:
- The Model 13C transmitter employed screen-grid modulation of the power amplifier stage. This is a form of low-level modulation in which audio voltage is coupled to the amplifier tube screen grids through a transformer, after being amplified in an audio power stage.
- The single audio amplifier stage in this transmitter was driven by audio from a carbon-type microphone, transformer-coupled to the audio tube control grid.[1]
One of the breakdowns in communication between the Itasca and NR16020 was due to the fact that Itasca's high-frequency transmitter (the one used to transmit on 7500 kcs) was not equipped with a microphone and voice modulation. The Itasca could only transmit using CW and Morse Code on that frequency. Tragically, this was the only frequency on which Earhart heard the Itasca's transmissions; if the Itasca could have transmitted to her in voice on this frequency, the problems with the direction finding might have been sorted out.