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What frequency did wireless telegraphs send and receive telegraphs at? Were there multiple frequencies?

For instance, this comment says Titanic operated around 1 MHz. Was there a range of frequencies available for use, or could operators choose any frequency and others would still be able to receive the signals?

I also read on some websites (for example, this one and this one) that wireless telegraphs spam the entire electromagnetic spectrum which is why they are illegal. Somehow, this seems hard to believe. I don't believe telegraphs are illegal, or that they spam the entire spectrum. Is there any truth in this?

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    \$\begingroup\$ en.wikipedia.org/wiki/Spark-gap_transmitter \$\endgroup\$ – szulat Jan 4 '17 at 13:39
  • \$\begingroup\$ Early radio communication was at LF and propagation was by ground wave, which means that over-the-horizon propagation is possible and the effect is greatly enhanced at night. As technology advanced, the useful spectrum expanded upwards and ionospheric reflection allowed long range communication. On HF bands, communication around the world is possible with low power when conditions are favourable, particularly at sunspot maxima when a few watts will do the job. \$\endgroup\$ – Chu Jan 4 '17 at 13:42
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    \$\begingroup\$ Titanic operated at 530 kHz and 900 kHz. Other equipment allowed tuning to different frequencies. See this: halifax-arc.org/sites/default/files/TitanicRadio1.pdf \$\endgroup\$ – Andy aka Jan 4 '17 at 13:56
  • \$\begingroup\$ So would these signals be picked up by radios today then? \$\endgroup\$ – InterLinked Jan 4 '17 at 14:03
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    \$\begingroup\$ Somehow, this seems hard to believe Why ? You post an opinion but no explanation why you are right. The pulses which were used on this old type of equipment are not "pure", they are made up from a wide range of frequencies (base frequency + many harmonics) that's why they take up too much frequency space and that's why they're illegal nowadays. \$\endgroup\$ – Bimpelrekkie Jan 4 '17 at 14:11
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Early radio transmission used telegraphy for communication using spark transmitters. Telegraphy is still used today, but does not use spark transmission (it is banned).

Spark transmitters were inefficient partly because they spread noise energy over a fairly broad bandwidth. However, energy was confined to a small part of the electromagnetic spectrum by resonance of coils and capacitors tuned to a desired frequency. In addition, antennas helped by radiating some frequencies more efficiently than others. Efforts to confine the broadband spark signal source to a narrower transmitted band not only improved efficiency, but allowed more users to communicate on nearby frequencies with less interference.
The frequency 500 kHz. was reserved for distress calls. Other frequencies were used for general communication traffic.
When vacuum-tube oscillators were introduced, it was possible to confine transmitted telegraphy signals to a single frequency. Telegraphy still requires some bandwidth to transmit information (see Nyquist rate), but beyond this bandwidth, very little noise is broadcast.
Your query is still of interest today, where much effort goes into generating coherent radio-frequency carriers free of adjacent noise sidebands.

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  • \$\begingroup\$ Can spark transmitters be used by ham operators? \$\endgroup\$ – InterLinked Jan 4 '17 at 16:00
  • \$\begingroup\$ when you say "other frequencies were used for general communication traffic" - could any frequencies be used or was communication restricted to a specific range? \$\endgroup\$ – InterLinked Jan 4 '17 at 16:02
  • \$\begingroup\$ @InterLinked If it were possible to refine a spark transmitter to transmit a signal identical to a modern coherent oscillator, it would be allowed. But doing so would require vast input power to generate meager radio power. Ham operators (among most other RF users) are required by law to refrain from interfering with other adjacent users - spark sidebands would violate this rule. \$\endgroup\$ – glen_geek Jan 4 '17 at 16:09
  • \$\begingroup\$ @InterLinked View this site for audible spark telegraphy example, and notes on bandwidth:<hammondmuseumofradio.org/spark.html> \$\endgroup\$ – glen_geek Jan 4 '17 at 16:39
  • \$\begingroup\$ @InterLinked Before 1912, spectrum was not allocated. Marconi company dominated usage. Because transmitting commutators turned at different rates, each transmitter had a different sound, so a receiving operator could tolerate some interference from a superimposed interfering signal. Geographical diversity helped reduce the interference problem. \$\endgroup\$ – glen_geek Jan 4 '17 at 17:04

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