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Effects of Solar Magnetic Storms on Early Telegraphy and Telephony

  1. Aug 23, 2007 #1
    Back in the early days of telegraph and telephone lines, electromagnetic storms emanating from the sun shut down communications services over land lines. As the decades progressed, solar storms no longer affected those lines.

    What engineering change was made to land lines to insulate them from the detrimental effects of solar storms?
     
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  3. Aug 23, 2007 #2

    berkeman

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    This looks like homework. I may move it to the Homework Help forums in a bit. In the mean time, remember the PF rule that you must show some of your own work in order to receive tutorial help on homework and coursework. How do you think EM storms would couple energy into long telegraph wires?
     
  4. Aug 23, 2007 #3
    The question arose from reading The Sun Kings: The Unexpected Tragedy of Richard Carrington and the Tale of How Modern Astronomy Began, by Stuart Clark. Want me to quote the passage and page number? << edited by berkeman >>
     
    Last edited by a moderator: Aug 23, 2007
  5. Aug 23, 2007 #4

    berkeman

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    Not so much the whole passage, but it would help to know more about what they say the detrimental effects were. What was the frequency of the interference?
     
  6. Aug 23, 2007 #5
    The frequency was whenever a solar storm occurred at the then unknown maximum in the eleven year sunspot cycle. Regarding an 1859 event, Clark wrote (pp.21-22):
    Satisfied my question is not homework?
     
  7. Aug 23, 2007 #6

    berkeman

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    By frequency, I meant the frequency of the electromagnetic radiation that was causing the interference. I'm not sure, but from the passage, it sounds like it was very low frequency RF, which the long wires of the telegraph system picked up and resonated with. With a long-wire antenna like that, you can get some pretty high voltages when the wire is resonant length. A wire that is a half wavelength long resonating at its fundamental frequency will have large voltage excursions at its two ends. If the frequency of the EM from the aurora was, say, around 1kHz, then the wavelength would be around 300km. Or if it was around 10kHz, then the wavelength would be 30km.

    As for differences today, surge protection circuits are very common on telecommunication wiring, and long-distance communication is more commonly done with microwave antennas and satellites. Any long-wire communication is definitely going to have surge protection to prevent the kinds of damage that the passage describes.

    Hope that helps.
     
  8. Aug 23, 2007 #7
    I don't know. I wasn't there in 1859. Why don't you ask Ben Franklin what the amperage was when he touched that key at the end of his kite?

    I doubt if commercial microwave transmission existed in the 1930's and early 1940's, yet AT&T and Western Union, both with plenty of long copper wires spanning the continent, didn't have problems with current-inducing auroras. So what was different between then and 1859 with respect to network protection that also allowed the continued transmission of voice and data?
     
  9. Aug 23, 2007 #8

    dlgoff

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    "So what was different between then and 1859 with respect to network protection that also allowed the continued transmission of voice and data?"

    Didn't berkeman answer this?
     
  10. Aug 23, 2007 #9

    berkeman

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    There may be more to the answer, I guess. Was the old telephony baseband? Telegraph was baseband, probably. Using higher frequency carriers would have moved the data away from the 1-10kHz interference range that I was guessing about, and allowed filtering to ensure data integrity better.

    So RJ, in addition to better surge protection on more modern long-haul communication wiring, the information on the wires is modulated on higher-frequency carriers than were probably used in the early days. I wonder if there is still more to the answer....
     
  11. Aug 23, 2007 #10
    No, I don't feel he did. I know what is done in the 21st century. I even know what was done in the late 20th century. The question is, what was done to protect networks and continue communications in the period before microwave and satellite technology, i.e., circa 1940 and before?
     
  12. Aug 23, 2007 #11
    I'm guessing from my history of communications that telegraphy was simplex or at best half-duplex and never multiplexed. Telephony would have been full duplex and probably multiplexed, but I don't know when multiplexing would have begun.

    But all of that I think is irrelevant. It makes no difference what frequencies were being used. The carrier was nothing more than copper wire strung on poles all over the continent. An EM storm would have induced a current, sometimes to life-threatening levels, in all such wires regardless of whatever carrier frequency was being used.

    To my knowledge, a surge protector is nothing more than a circuit breaker. If tripped, it should make the line unusable, until it was reset manually or automatically. However, it is my understanding communications continued unabated and unaffected by such storms after the networks were protected by whatever means employed.

    Could the wires have been sheathed inside a metal casing, that casing grounded at each telegraph or telephone pole across the land? That may have neutralized any induced current while leaving communications within the cable unaffected.

    By a metal sheath, I am not referring to coaxial cable. Although invented in 1880 by that unsung genius Oliver Heaviside, and reinvented several more times in later years, it wasn't until about 1940 that coaxial cable came into use, I think for the transmission of television signals.

    All telephone and telegraph poles carry a lightning arrestor that is grounded. However, the sheathed cable would have had to be independently grounded, else a lightning strike could adversely affect the cable if not permanently fry it.

    There is another problem with sheathed cables if that is what was used. Every wire on every telephone pole ran through a glass insulator. Those insulators, in their varied shapes and colors, are major collector's items today. It would not have made much sense to run a sheathed cable through a glass insulator, only to have the metal casing grounded at each and every pole.
     
  13. Aug 23, 2007 #12

    berkeman

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    I wasn't refering to duplex versus simplex so much, I was referring to baseband versus modulated communication channels.

    No, the reason that modulated communication is more robust than baseband comm, is that you can modulate the information up to some carrier frequency that is away from the noise frequency, and use bandpass filters at the receivers to greatly improve your signal to noise ratio (SNR). For example (assuming my guesses at the aurora EM interference were close, which is not neccessarily the case), if the aurora EM energy was mostly concentrated in 1-10kHz, and you chose to mix an audio information channel with a 1MHz carrier, then you could use a bandpass filter at the receiver a few kHz wide, centered on 1MHz, which would give you about 40dB of attenuation of the noise per low-side pole. That's a lot of rejection of that noise!

    Not exactly. Most surge protection is placed in parallel, not in series. Surge protectors limit the voltage excursion of a wire, basically clamping it within some number of volts with respect to Earth ground. Like a 470V MOV (metal oxide varistor) is high impedance until the voltage on the wire gets close to 470V, and then it progressively gets lower and lower impedance as the voltage tries to rise through 470V. It acts as a low impedance clamp around 470V, until its power dissipation and clamp current get exceded for too long, in which case it pops and fails. MOVs and other surge protection devices are sized to be able to withstand the maximum forseeable transients, and not get to that failure condition.

    That's a good point -- whenever conduit got introduced, that would have been a big step up in communication integrity. But for long wire communication lines, I don't think they went to conduit very much -- maybe for underground lines, but not for overhead wires.





    I think the glass/porcelin (sp?) insulators are only for the HV AC mains transmission lines on the top tier of the poles. The mid-tier communications lines (cable TV, etc.) are not on insulators.


    BTW, one of your points brought an interesting additional historic consideration to mind. I wonder what kinds of surge protection tecnnologies were available through the years.... Certainly semiconductor surge protectors like TVSs have only been available recently. Even MOVs take some manufacturing expertise that would seem to be a relatively recent development. Gas discharge tubes (which are used a LOT) are pretty basic, but I don't know if they were used in the early days of telegraphy.

    This thread is intriguing.... I wonder if there is a good technical description somewhere of the earliest Morse code telegraphy lines in the US and elsewhere.... Time for some google searching. :smile:
     
    Last edited: Aug 23, 2007
  14. Aug 24, 2007 #13
    Many of those lines ran along railroad right of ways, especially in the West, as late as the 1960s and later. Dozens of wires were mounted on each pole, spread across multiple crossbars, each wire with its own glass insulators. These wires were not electric transmission lines, but telephone and telegraph wires. These I saw with my own eyes.

    My question still remains unanswered: What did electrical engineers do between 1910 and 1940 to protect telephone and telegraph networks from EM storms that also enabled the continued operation of those networks? EM storms often lasted days and were not a brief interruption.
     
  15. Aug 24, 2007 #14

    dlgoff

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    "These I saw with my own eyes."

    Me too. But did you ever listen to them sing? I grew up around railroad tracks and could hear them as they carried their data.

    "What did electrical engineers do ..."

    Well maybe they just let the systems go down during these EM storms. How much did they know about these storms back then?
     
  16. Aug 24, 2007 #15
    I have heard them sing, but I was never quite sure if that was caused by electrical impulses or a simple resonance with a breeze. In any event, the sounds I heard were steady ones, akin to a low steady hum, not changing with any signal modulation ostensibly being carried by the wires.

    That led me to conclude the sounds I heard were wind generated, although many times I felt the wind was insufficient to create a resonance. Moreover, the effect was not universally noticed on all pairs of poles. Sometimes, the wires would sing, but the wires on either side were silent.

    That is the conclusion I am coming to. I did not know for sure, but I was unaware of any communication interruptions in the period 1910-1940, that from my reading of history, including the history of the telegraph. I therefore assumed electrical engineers had had to have done something to protect their networks while still allowing communications to be transmitted and received despite the detrimental effects of EM storms.

    I have subsequently discovered that was not the case. There are numerous sources documenting the complete shutdown of these networks. Operators at the time just lived with it, learned to work with it, or went fishing until normalcy was restored. There may have been some shielding of some wires, but it was more the exception than the rule.

    Back when? By 1930, I would presume scientists and engineers knew all they needed to know about the cause and effect of these EM storms.
     
    Last edited: Aug 24, 2007
  17. Aug 25, 2007 #16
    It comes to my mind that the impedance of the communication lines was much lower before the invention of the vacuum tube. They had to run lots of current through the lines to actuate the receivers.

    Low impedance cross-country lines are susceptable to EM storms yet today. Just a few years ago the electric power distribution systemm was knocked out in Canada by an EM storm.
     
  18. Aug 25, 2007 #17
    To my knowledge, the current through communication lines was and is direct current, so I am not certain if impedance is an appropriate term here. Isn't impedance a measure of the total resistance in an alternating circuit?

    Power transmission lines, as opposed to communication lines, continue to be affected by EM storms because of the added surge.
     
  19. Aug 25, 2007 #18
    Actually impedance includes resistance: z^2 = r^2 - X^2 where z is impedance, r is resistance, X is the AC reactance. But, you are right, I should have said resistance instead of impedance.

    As I understand what happens in power grids during EM storms, the strom induces dc current into the transmission lines. Normally, this is just shorted-out by the substation transformers, but sometime the storm can induce enough current to saturate the transformer core, and then the ac current will become very large and trips the breaker.
     
  20. Aug 26, 2007 #19
    I dont know if this is correct answer, just an idea:

    I read that the first telegraph lines were set up whith just one wire, using the earth as the "return" wire. This caused a lot of interference signals and then the lines were changed to "two wires".

    Nowadays all telephone lines are two wires and "balanced" and the wires are twisted pairs to reduce the interferences. ( and these telephone lines are baseband ).

    Nowadays all telephone lines are protected agaisnt overvoltages with VDRs ( ¿? ) or other devices.
     
  21. Aug 26, 2007 #20
    ¿What is "baseband"?
     
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