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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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InterLinked
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    https://en.wikipedia.org/wiki/Spark-gap_transmitter – szulat Jan 04 '17 at 13:39
  • 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. – Chu Jan 04 '17 at 13:42
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    Titanic operated at 530 kHz and 900 kHz. Other equipment allowed tuning to different frequencies. See this: http://www.halifax-arc.org/sites/default/files/TitanicRadio1.pdf – Andy aka Jan 04 '17 at 13:56
  • So would these signals be picked up by radios today then? – InterLinked Jan 04 '17 at 14:03
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    *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. – Bimpelrekkie Jan 04 '17 at 14:11
  • So yes, your radio might pick that up depending on the type (AM more sensitive than FM, DAB might not be disturbed at all). In the old days there were only a few transmitters so it somehow worked. Now the "radio space" is more cramped and we have to "mind the neighbours" so to say. – Bimpelrekkie Jan 04 '17 at 14:14
  • Spark transmitters spanned a large proportion of the e-m spectrum (c.f. Ignition noise from an unsuppressed spark plug). The bigger the spark, the more the range. But in those days there was no electronics to interfere with. – Chu Jan 04 '17 at 14:27
  • Does anyone know the legality of spark transmitters these days? Could I set up a wireless telegraph and start using it, or can we only use wired telegraphs these days? – InterLinked Jan 04 '17 at 15:13
  • Get a ham license and you can do morse across the world if you want. – pjc50 Jan 04 '17 at 15:20
  • @pjc50 And I can just use the frequencies I am assigned as I wish or do I need to also transmit my call sign when sending a telegram? Could I give others permission to operate the same frequencies so we could send and receive telegrams wirelessly (obviously they wouldn't be private)? – InterLinked Jan 04 '17 at 15:43
  • You don't usually get your *own* frequency, they're assigned to a purpose and category of use. Although in practice you can pick a CW spot frequency that nobody else is using and chat away in Morse. See e.g. http://rsgb.org/main/operating/band-plans/vhf-uhf/144mhz-band/ – pjc50 Jan 04 '17 at 15:49

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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.

glen_geek
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  • Can spark transmitters be used by ham operators? – InterLinked Jan 04 '17 at 16:00
  • when you say "other frequencies were used for general communication traffic" - could any frequencies be used or was communication restricted to a specific range? – InterLinked Jan 04 '17 at 16:02
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    @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. – glen_geek Jan 04 '17 at 16:09
  • @InterLinked View this site for audible spark telegraphy example, and notes on bandwidth: – glen_geek Jan 04 '17 at 16:39
  • @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. – glen_geek Jan 04 '17 at 17:04
  • Did people have any good way of measuring the frequencies radios produced, e.g. by using some processes that physically generate harmonic-rich signals at known frequencies, and observing which frequencies seem to contain components that resonate strongly within a tuning arrangement? – supercat Jan 04 '17 at 17:32
  • @glen_geek The website you linked does not work – InterLinked Jan 04 '17 at 17:38
  • @InterLinked: delete the closing ">;" from glen_geek's link - that should work. – Peter Bennett Jan 04 '17 at 17:44