[CW] SAQ Live Stream

Wed Jul 8 00:36:26 EDT 2020

What's a "firehorse complex?"

The alternator didn't have modulation, but when I heard SAQ the signal
sounded like it had a tone on it, maybe the effect of long range
propagation, I don't know.

>From Wikipedia (see below)

73

DR

Beginning around 1905 continuous wave
<https://en.m.wikipedia.org/wiki/Continuous_wave> (CW) transmitters began
to replace spark transmitters for radiotelegraphy because they had much
greater range. The first continuous wave transmitters were the Poulsen arc
<https://en.m.wikipedia.org/wiki/Poulsen_arc> invented in 1904 and the
Alexanderson
alternator <https://en.m.wikipedia.org/wiki/Alexanderson_alternator> developed
1906-1910, which were replaced by vacuum tube transmitters beginning around
1920.[21]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Phillips1-21>

The continuous wave radiotelegraphy signals produced by these transmitters
required a different method of reception.[93]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Lauer-93>[94]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Phillips9-94> The
radiotelegraphy signals produced by spark gap transmitters consisted of
strings of damped waves <https://en.m.wikipedia.org/wiki/Damped_wave> repeating
at an audio rate, so the "dots" and "dashes" of Morse code were audible as
a tone or buzz in the receivers' earphones. However the new continuous wave
radiotelegraph signals simply consisted of pulses of unmodulated carrier
<https://en.m.wikipedia.org/wiki/Carrier_signal> (sine waves
<https://en.m.wikipedia.org/wiki/Sine_wave>). These were inaudible in the
receiver headphones. To receive this new modulation type, the receiver had
to produce some kind of tone during the pulses of carrier.

The first crude device that did this was the tikker
<https://en.m.wikipedia.org/wiki/Tikker>, invented in 1908 by Valdemar
Poulsen <https://en.m.wikipedia.org/wiki/Valdemar_Poulsen>.[45]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Marriott-45>[93]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Lauer-93>[95]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-McNicol1-95> This
was a vibrating interrupter with a capacitor
<https://en.m.wikipedia.org/wiki/Capacitor> at the tuner output which
served as a rudimentary modulator
<https://en.m.wikipedia.org/wiki/Modulator>, interrupting the carrier at an
audio rate, thus producing a buzz in the earphone when the carrier was
present.[8]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Lee2-8> A similar
device was the "tone wheel" invented by Rudolph Goldschmidt
<https://en.m.wikipedia.org/wiki/Rudolph_Goldschmidt>, a wheel spun by a
motor with contacts spaced around its circumference, which made contact
with a stationary brush.
<https://en.m.wikipedia.org/wiki/File:Heterodyne_radio_receiver_circuit_1920.png>
Fessenden's heterodyne radio receiver circuit

In 1901 Reginald Fessenden
<https://en.m.wikipedia.org/wiki/Reginald_Fessenden> had invented a better
means of accomplishing this.[93]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Lauer-93>[95]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-McNicol1-95>[96]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Patent1050441-96>
[97] <https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Hogan-97> In
his *heterodyne receiver* an unmodulated sine wave radio signal at a
frequency *fO* offset from the incoming radio wave carrier *fC* was applied
to a rectifying detector such as a crystal detector
<https://en.m.wikipedia.org/wiki/Crystal_detector> or electrolytic detector
<https://en.m.wikipedia.org/wiki/Electrolytic_detector>, along with the
radio signal from the antenna. In the detector the two signals mixed,
creating two new *heterodyne <https://en.m.wikipedia.org/wiki/Heterodyne>* (
beat <https://en.m.wikipedia.org/wiki/Beat_%28acoustics%29>) frequencies at
the sum *fC* + *fO* and the difference *fC* − *fO* between these
frequencies. By choosing *fO* correctly the lower heterodyne *fC* − *fO* was
in the audio frequency <https://en.m.wikipedia.org/wiki/Audio_frequency> range,
so it was audible as a tone in the earphone whenever the carrier was
present. Thus the "dots" and "dashes" of Morse code were audible as musical
"beeps". A major attraction of this method during this pre-amplification
period was that the heterodyne receiver actually amplified the signal
somewhat, the detector had "mixer gain".[95]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-McNicol1-95>

The receiver was ahead of its time, because when it was invented there was
no oscillator capable of producing the radio frequency sine wave *fO* with
the required stability.[98]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Nahin2-98> Fessenden
first used his large radio frequency alternator
<https://en.m.wikipedia.org/wiki/Alternator>,[8]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Lee2-8> but this
wasn't practical for ordinary receivers. The heterodyne receiver remained a
laboratory curiosity until a cheap compact source of continuous waves
appeared, the vacuum tube electronic oscillator
<https://en.m.wikipedia.org/wiki/Electronic_oscillator>[95]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-McNicol1-95> invented
by Edwin Armstrong <https://en.m.wikipedia.org/wiki/Edwin_Armstrong>
and Alexander
Meissner <https://en.m.wikipedia.org/wiki/Alexander_Meissner> in 1913.[45]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Marriott-45>[99]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-McNicol16-99> After
this it became the standard method of receiving CW radiotelegraphy. The
heterodyne oscillator is the ancestor of the *beat frequency oscillator
<https://en.m.wikipedia.org/wiki/Beat_frequency_oscillator>* (BFO) which is
used to receive radiotelegraphy in communications receivers
<https://en.m.wikipedia.org/wiki/Communications_receiver> today. The
heterodyne oscillator had to be retuned each time the receiver was tuned to
a new station, but in modern superheterodyne
<https://en.m.wikipedia.org/wiki/Superheterodyne> receivers the BFO signal
beats with the fixed intermediate frequency
<https://en.m.wikipedia.org/wiki/Intermediate_frequency>, so the beat
frequency oscillator can be a fixed frequency.

Armstrong later used Fessenden's heterodyne principle in his
superheterodyne receiver *(below)*.[95]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-McNicol1-95>[8]
<https://en.m.wikipedia.org/wiki/Radio_receiver#cite_note-Lee2-8>
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