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Can the generator transmit? - VLF electromechanical transmitter

TechEkspert 7182 11
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  • Can the generator transmit? - VLF electromechanical transmitter
    From the electronics archive - Electromechanical VLF transmitter

    Can the generator transmit? The antenna can transmit by radiating RF energy delivered by the transmitter in the form of electromagnetic waves. The transmitter output signal can be modulated both in amplitude and frequency, which allows information to be transmitted via radio.

    Can a generator be a transmitter? An alternator can supply energy in the form of alternating current. It is easy to imagine a device delivering 50 Hz alternating current, a frequency much lower than the radio frequencies known today. It would be quite difficult to build an antenna system that works effectively at 50Hz (although ELF (Extreme Low Frequency) 3-30Hz and SLF (Super Low Frequency) 30-300Hz were used for communication with submarines, which required MW power).

    Can the generator transmit? - VLF electromechanical transmitter

    VLF (Very Low Frequency) range 3-30kHz
    You will not find the VLF band in a typical radio receiver, but in the past this band was used, for example, for telegraph communication. Today, there is still a transmitter that uses an electromechanical generator that uses an Alexanderson alternator. In Poland, there was the Transatlantic Radiotelegraphic Center in Warsaw, which also based its operation on a generator in the form of a high-frequency generator.

    SAQ Grimeton station near Varberg in Sweden - 17.2 kHz
    It is easy to calculate that a 50Hz 3000 rpm generator would have to rotate 344 times faster, which is rather difficult to achieve. Alexanderson's alternator had an appropriate design allowing for operation at a higher frequency and at a lower rotational speed (a large number of pole pairs). Alexanderson's generator was powered by an electric motor equipped with a gear increasing the speed of rotation. The transmitter in Grimeton reached a power of 200 kW, it used a 1.9 km long antenna suspended on six 127 m steel masts. The station was one of eighteen transmitters making up the global communication network.



    Can the generator transmit? - VLF electromechanical transmitter

    The "RF" energy was modulated with a magnetic amplifier controlled by a relay and a telegraph key. The transmitter is activated on Christmas Eve and usually on Alexanderson's Day (last Sunday in June or first Sunday in July, whichever is closer to July 2).
    You can get a QSL card for confirmation of transmission receipt.
    Interestingly - you can also build a receiver using an electromechanical oscillator:
    http://www.wireless.org.uk/mechrx.htm
    However, this is more of a hobby than a practical project.

    We are witnessing the rapid development of technology, it is already hard to believe that there used to be 200kW radio transmitters that did not use lamps or transistors in the transmitter's RF circuit.

    SAQ transmitter generator frequency tuning:


    The next additional broadcast on February 13, 2015. at 15:00 UTC
    http://alexander.n.se/evenemang/world-radio-day-transmission/

    Will you try to receive the SAQ transmission?

    Sources:
    http://alexander.n.se/in-english/
    http://www.grimetonradio.se/index.php/english
    http://www.vlf.it
    http://pl.wikipedia.org/wiki/Alternator_Alexandersona
    http://pl.wikipedia.org/wiki/Radiostacja_Varberg_w_Grimeton

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    TechEkspert
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  • #2
    maxxim
    Level 15  
    Do you know when the next broadcast in this band will be?
  • #4
    TechEkspert
    Editor
    Next week on Saturday, October 24, 2015. the "SAQ" station will broadcast at 10: 00UTC (12:00). The tuning will start at 09:30 UTC (11:30).

    http://alexander.n.se/in-english/saq-transmission/

    This time I will try to receive the broadcast content, is anyone also planning to receive?
    Would an electric or magnetic responsive antenna be better?
  • #5
    maxxim
    Level 15  
    I'm going to pick up the broadcast. I am not sure if my set, i.e. active antenna and sound card + SAQrx, will work ;) . It's the first time I'm going so low !!
  • #6
    KaW
    Level 34  
    Why does the author use the words "w.cz". There is no RF energy here. There is an electromagnetic wave - it has a low frequency and high power.
    Requires large transmit antennas and large receive antennas.
  • #7
    TechEkspert
    Editor
    @maxxim maybe we will be able to exchange experiences with SAQ reception.
    A few hours before the broadcast, I had assembled two makeshift amplifiers.
    One based on the design DL1DBC using an operational amplifier and an antenna responding to an electric component. As the antenna, I prepared a printed circuit board and an ordinary telescopic antenna.
    The second amplifier was based on the design easyloop I used a cathode ray tube demagnetizing coil as the antenna.

    To set the position of the magnetic antenna, a tool that calculates the azimuth after entering the coordinates of two locations may be useful https://www.fcc.gov/encyclopedia/distance-and-azimuths-between-two-sets-coordinates ( SAQ transmitter coordinates ).

    Before SAQ transmissions, I connected the outputs of two amplifiers to both channels of the sound card. In an urban environment, unfortunately, I received mainly mains hum and a signal at the horizontal frequency of 15625Hz coming from working TV sets. I probably managed to hit the moment when one of the receivers was turned on.
    Can the generator transmit? - VLF electromechanical transmitter

    When the tuning and transmission started, I checked the signal with one of the SDR receivers providing audio from the browser: Wide-band WebSDR . Here is an example of a receiver located in Poland sp3pgx - WebSDR .

    Unfortunately, the built-in amplifiers did not allow for the SAQ signal reception, maybe the interference level was too high or I made a mistake.
    Can the generator transmit? - VLF electromechanical transmitter

    I am going to return to the topic of VLF frequency reception, especially since the receivers reacting to the electric component are quite simple in construction. The role of the antenna can be used as an aluminum box Audio Antenna by Pierluigi Poggi IW4BLG , B3CKS-ANTENNA
    You can find many ideas for making a VLF receiver:
    http://www.techlib.com/electronics/vlfwhistle.htm
    http://www.vlf.it/romero2/explorer-e202.html

    I found a description of a rather interesting receiver SP9HSQ - electrical component receiver perhaps its design will allow for better results.

    There are also materials describing the construction of the receiver with an "electric" and "magnetic" antenna:
    ELF-VLF multi-receiver

    Perhaps next time I will be able to better prepare for pickup.


    @KaW rightly, it is difficult to talk about RF at 17.2kHz, it is the output signal of the transmitter and the term "RF" may be a kind of abuse here, as for the receiving antennas they may or may not be large, e.g. MiniWhip or slightly higher http://sp9moa.moa.edu.pl/odebralismy-depesze-z-radiostation-grimeton-saq/.
  • #8
    KaW
    Level 34  
    The definitions and descriptions of WIKIPEDIA are the same. This lowers the value of this material.
    Element of basic knowledge of electromagnetic wave is omitted.
  • #10
    TechEkspert
    Editor
    When will you receive the transmission, what receiver and antenna?
    The description of the experiments with reception should be included in the articles.
  • #11
    Marek LUB
    Level 12  
    I refreshed the topic in a survey, not counting on interest, thanks for the response. Have you provided some examples of receivers that you would recommend?
    There are two pickup dates, birthday and holiday, I don't have a plan. Heard about some games at around 40kHz. Apparently, this signal is always or was, knowledge from several years ago. I could train.
  • #12
    TechEkspert
    Editor
    In an open space, I would lean towards the receiver with the GP antenna reacting to the electrical component. In the housing, you can use an antenna that responds to a magnetic component.