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  1. #31
    Jeff Liebermann
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency

    Radium <[email protected]> hath wroth:

    >On Jun 30, 7:43 pm, Jeff Liebermann <[email protected]> wrote:
    >
    >> The carrier does NOT vary in amplitude. If
    >> it did, that would be modulating the carrier, which is the job of the
    >> modulator, not whatever is producing the carrier.

    >
    >Exactly. The modulator signal modulates the carrier wave. If there is
    >no modulator signal, then the carrier does not vary by amplitude or by
    >anything.


    Brilliant. Yes, if there is no signal input, there's no change in
    output.

    Incidentally, in an AM system, the carrier does NOT change. You can
    see that on a spectrum analyzer. Modulate all you want and the
    carrier stays put at 50% of the total power output. The rest of the
    power is split between the upper and lower side bands. If there is no
    modulation input, then the side bands disappear, but the carrier just
    stays there.

    As someone mentioned, there is usually some residual FM on the carrier
    usually caused by sloppy power supply regulation. Also, some
    synthesizer noise. A well designed AM broadcast transmitter doesn't
    have much of this junk present. The problem is that the FM that
    appears on the carrier also appears on all the side bands. It doesn't
    hurt if the carrier has a little residual FM, but any such junk on the
    sidebands will result in a substantial increase in audible noise by
    mixing with the audio.

    >One poster stated that the signal with the higher-frequency is
    >automatically the carrier wave while the signal with the lower-
    >frequency is automatically the modulator wave.


    That was me.

    >This is not true.


    Prove it. I explained how it works and why quite adequately. I
    didn't even need to resort to formulas and calculations. The
    multiplier (mixer) modulator inputs are symmetrical and identical.
    Therefore the inputs are also symmetrical and indistinguishable. I
    also provided a simple audio test you can do in your spare time to
    demonstrate how it works.

    Now, convince me that the multiplier (mixer) waveform would be
    different depending on which input was the carrier or modulation.

    >What
    >I was trying to say is that an AM radio carrier wave cannot vary
    >significantly by anything other than its amplitude [though, as one
    >poster pointed out, the AM carrier can experience extremely-negligible
    >variations in frequency]. If an AM radio signal has that restriction,
    >it is the carrier wave. If an AM radio signal does not have that
    >restriction, then it is the modulator wave. This is true, even if the
    >AM carrier wave is of a lower-frequency than the modulator wave.
    >That's what I was trying to say.


    I give up. What you've done is created a word salad. That's where
    you have a mess of buzzwords, shredded together, mixed with some
    window dressing, and served in a manner to imply that you have a clue
    what you're disgorging. Even the most basic concepts are not sinking
    in. You've also ignored multiple suggestions to read some very fine
    sources on how RF and modulation works. Open book, insert face, and
    come back when you have a clue as to the basics.

    >In AM radio, determining which is the carrier wave and which is the
    >modulator wave is not by which has the higher frequency but rather by
    >which has the restriction that I stated.


    Wrong. With AM it's easy. The higher frequency is always the
    carrier. Can you give me a diagram or a commonly used communications
    system where the reverse might be true? I can't.

    >If there is no modulator signal, then no carrier signal of any type
    >[AM, FM, etc.] will vary by any quality [frequency, amplitude, phase,
    >etc.]


    Yawn...

    --
    Jeff Liebermann [email protected]
    150 Felker St #D http://www.LearnByDestroying.com
    Santa Cruz CA 95060 http://802.11junk.com
    Skype: JeffLiebermann AE6KS 831-336-2558



    See More: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency




  2. #32
    John Smith I
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency

    Don Bowey wrote:

    > ...
    > You are hearing the effects of the sidebands, not the Carrier.


    DUH! And, you only have the sidebands as a result of the
    carrier/modulation ...

    > In a properly designed transmitter the Carrier amplitude does not change
    > with modulation. I have better tools than FM receivers to prove that fact
    > and theory agree for AM.


    And the time to argue the insignificant ... sharpen that razor blade,
    you can then successfully split much narrower hairs ...

    JS





  3. #33
    Radium
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency

    On Jun 30, 12:55 pm, John Smith I <[email protected]> wrote:

    > Use simple logic, you can modulate a dc (0 Hz) with higher freq (voice),
    > (hint, your telephone line is an example) right?


    The telephone does not use either AM or FM. It is simply the
    electrical equivalent of the sound that gets into the microphone. You
    input a 1 KHz tone into the microphone, telephone lines will carry a 1
    KHz AC current to the destination. The louder the sound into the
    microphone, the stronger the amperage in the telephone lines.




  4. #34
    Don Bowey
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency

    On 6/30/07 8:50 PM, in article [email protected], "John Smith I"
    <[email protected]> wrote:

    > Don Bowey wrote:
    >
    >> ...
    >> You are hearing the effects of the sidebands, not the Carrier.

    >
    > DUH! And, you only have the sidebands as a result of the
    > carrier/modulation ...


    So what? You implied or inferred that what was heard from the FM radio was
    caused by the AM Carrier. Leave out the Carrier and you will hear the same
    thing.

    >
    >> In a properly designed transmitter the Carrier amplitude does not change
    >> with modulation. I have better tools than FM receivers to prove that fact
    >> and theory agree for AM.

    >
    > And the time to argue the insignificant ... sharpen that razor blade,
    > you can then successfully split much narrower hairs ...


    It is important that we not confuse a person new to electronics by the type
    of inane points you make. It doesn't matter a whit if someone's AM
    transmitter Carrier shifts on power peaks due to poor regulation. It has
    nothing to do with "AM" and everything to do with poor design.

    Side issues don't help the new folks.


    >
    > JS
    >
    >





  5. #35
    Don Bowey
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency

    On 6/30/07 9:01 PM, in article
    [email protected], "Radium"
    <[email protected]> wrote:

    > On Jun 30, 12:55 pm, John Smith I <[email protected]> wrote:
    >
    >> Use simple logic, you can modulate a dc (0 Hz) with higher freq (voice),
    >> (hint, your telephone line is an example) right?

    >
    > The telephone does not use either AM or FM. It is simply the
    > electrical equivalent of the sound that gets into the microphone. You
    > input a 1 KHz tone into the microphone, telephone lines will carry a 1
    > KHz AC current to the destination. The louder the sound into the
    > microphone, the stronger the amperage in the telephone lines.
    >



    Good for you for catching that one. The effect of microphone current has
    noting at all to do with AM.




  6. #36
    DTC
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency

    Mike Kaliski wrote:
    > ELF communications are carried out at very slow data rates, only a few
    > characters per hour at best.


    Actually its on the order of several characters per minute using a 64
    character "alphabet".

    > It is possible to communicate at a base band frequency of 0Hz. This is what
    > happens when you talk down a hard wired telephone or intercom. At a
    > telephone exchange (switching centre), the signals from each line are
    > modulated onto a higher frequency for onward transmission down a trunk wire
    > cable or fibre optic cable. The multiplexed high frequency modulated signals
    > are down converted back to audio frequencies once they reach the intended
    > destination.


    In the old T carrier (before 24 channel digital T1) carrier, each telephone
    conversation was modulated onto a low frequency radio frequency AM signal
    ranging from (and don't quote me as its been over thirty years since I
    worked T spans) 50 KC to 200 KC. Very similar in principle to the 5 kc wide
    AM radio station signals on the 530 kHz to 1700 kHz AM broadcast band.



  7. #37
    DTC
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency

    Radium wrote:
    > You
    > input a 1 KHz tone into the microphone, telephone lines will carry a 1
    > KHz AC current to the destination. The louder the sound into the
    > microphone, the stronger the amperage in the telephone lines.


    On a side note, its actually voltage modulation towards the subscribe and
    current modulation back to the central office. The earpiece is a high
    impedance (2,000 ohm) device that responds to voltage variations. The
    carbon microphone element 220 to 200 ohms modulates the talk battery current.




  8. #38
    Jeff Liebermann
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency

    DTC <no_spam@move_along_folks.foob> hath wroth:

    >Mike Kaliski wrote:
    >> ELF communications are carried out at very slow data rates, only a few
    >> characters per hour at best.

    >
    >Actually its on the order of several characters per minute using a 64
    >character "alphabet".
    >
    >> It is possible to communicate at a base band frequency of 0Hz. This is what
    >> happens when you talk down a hard wired telephone or intercom. At a
    >> telephone exchange (switching centre), the signals from each line are
    >> modulated onto a higher frequency for onward transmission down a trunk wire
    >> cable or fibre optic cable. The multiplexed high frequency modulated signals
    >> are down converted back to audio frequencies once they reach the intended
    >> destination.


    >In the old T carrier (before 24 channel digital T1) carrier, each telephone
    >conversation was modulated onto a low frequency radio frequency AM signal
    >ranging from (and don't quote me as its been over thirty years since I
    >worked T spans) 50 KC to 200 KC. Very similar in principle to the 5 kc wide
    >AM radio station signals on the 530 kHz to 1700 kHz AM broadcast band.


    Argh, that brings back fond nightmares of Ma Bell. 4Hz per voice
    channel with FDM (frequency division mux). Most were FM systems, but
    there were some AM implimentations (to avoid patent infringement).
    Later, there were SSB systems that doubled the number of channels.

    No voice Spectrum BW
    channels KHz kHz AT&T ITU-T
    12 60-108 48 Group Group
    60 312-552 240 Supergroup Supergroup
    300 812-2044 1232 Mastergroup
    600 564-3084 2520 Mastergroup
    3600 564-17548 16984 Jumbogroup


    --
    Jeff Liebermann [email protected]
    150 Felker St #D http://www.LearnByDestroying.com
    Santa Cruz CA 95060 http://802.11junk.com
    Skype: JeffLiebermann AE6KS 831-336-2558



  9. #39
    John Smith I
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency

    Radium wrote:
    ....

    You miss the simple point, the dc is the carrier ... instead of dc, you
    could put a 1 hz signal on the line and modulate it with your voice,
    indeed, you can put a 30 hz signal on the line and modulate it with your
    voice--if you can tollerate a bad 30 hz hum! But, who knows, perhaps
    you are tone deaf to the 30 hz hum and would like it ...

    JS



  10. #40
    John Smith I
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency

    Don Bowey wrote:

    > ...


    You are an idiot ... bother some one who has the time to take you to
    task ...

    JS



  11. #41
    kev
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency

    Jeff Liebermann wrote:
    > DTC <no_spam@move_along_folks.foob> hath wroth:
    >
    >> Mike Kaliski wrote:
    >>> ELF communications are carried out at very slow data rates, only a few
    >>> characters per hour at best.

    >> Actually its on the order of several characters per minute using a 64
    >> character "alphabet".
    >>
    >>> It is possible to communicate at a base band frequency of 0Hz. This is what
    >>> happens when you talk down a hard wired telephone or intercom. At a
    >>> telephone exchange (switching centre), the signals from each line are
    >>> modulated onto a higher frequency for onward transmission down a trunk wire
    >>> cable or fibre optic cable. The multiplexed high frequency modulated signals
    >>> are down converted back to audio frequencies once they reach the intended
    >>> destination.

    >
    >> In the old T carrier (before 24 channel digital T1) carrier, each telephone
    >> conversation was modulated onto a low frequency radio frequency AM signal
    >> ranging from (and don't quote me as its been over thirty years since I
    >> worked T spans) 50 KC to 200 KC. Very similar in principle to the 5 kc wide
    >> AM radio station signals on the 530 kHz to 1700 kHz AM broadcast band.

    >
    > Argh, that brings back fond nightmares of Ma Bell. 4Hz per voice
    > channel with FDM (frequency division mux). Most were FM systems, but
    > there were some AM implimentations (to avoid patent infringement).
    > Later, there were SSB systems that doubled the number of channels.
    >
    > No voice Spectrum BW
    > channels KHz kHz AT&T ITU-T
    > 12 60-108 48 Group Group
    > 60 312-552 240 Supergroup Supergroup
    > 300 812-2044 1232 Mastergroup
    > 600 564-3084 2520 Mastergroup
    > 3600 564-17548 16984 Jumbogroup
    >
    >

    That does bring back memories. I worked on STC built systems that used
    AM modulation using Double-Balanced Modulators and depending on "Group"
    classification used either the lower or upper sideband. Up to the 60
    "voice" Ch's, we had some low Baud rate Modems on as well with the
    signalling frequency disabled, the spectrum usage was the the same
    however the next step up was 16 Supergroups using 60-4028KHz with
    Supergroup 2 not being translated. We also had a 30 Ch PCM link which
    worked very well apart from the "Regenerators" being susceptible to
    lightning.



  12. #42
    Ian Jackson
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-low carrier frequency

    In message <[email protected]>, cledus
    <[email protected]> writes
    >Radium wrote:
    >> Hi:
    >> Please don't be annoyed/offended by my question as I decreased the
    >> modulation frequency to where it would actually be realistic.
    >> I have a very weird question about electromagnetic radiation,
    >> carriers, and modulators.
    >>
    >>
    >>
    >>
    >>
    >> No offense but please respond with reasonable answers & keep out the
    >> jokes, off-topic nonsense, taunts, insults, and trivializations. I am
    >> really interested in this.
    >> Thanks,
    >> Radium
    >>

    >
    >
    >The fundamental answer is no, it is not possible to generate AM where
    >the baseband signal is a pure 20 kHz sinewave and Fc<20kHz. The reason
    >is that the modulated waveform consists of the sum of a sinewave at Fc,
    >a sinewave at Fc+20kHz, and a sinewave at Fc-20kHz. If Fc<20kHz then
    >one of the components becomes a "negative" frequency. So the carrier
    >must be greater than the baseband signal to prevent this.
    >

    I'm afraid that this is not correct. The 'laws of physics' don't
    suddenly stop working if the carrier is lower than the modulating
    frequency. However, there's no need to get into complicated mathematics
    to illustrate this. Here is a simple example:

    (a) If you modulate a 10MHz carrier with a 1MHz signal, you will produce
    two new signals (the sidebands) at the difference frequency of 10 minus
    1 = 9MHz, and the sum frequency of 10 plus 1 = 11MHz. So you have the
    original carrier at 10MHz, and sideband signals at 9 and 11MHz (with a
    balanced modulator - no carrier - only 9 and 11MHz).

    (b) If you modulate a 1MHz carrier with a 10MHz signal, you will produce
    two new signals (the sidebands) at the difference frequency of 1 minus
    10 = minus 9MHz, and the sum frequency of 1 plus 10 = 11MHz. The
    implication of the negative 'minus 9' MHz signal is that the phase of
    the 9MHz signal is inverted, ie 180 degrees out-of-phase from 9MHz
    produced in (a). So you have the original carrier at 1MHz, and sidebands
    at 9 and 11MHz (again, with a balanced modulator - no carrier - only 9
    and 11MHz).

    The waveforms of the full composite AM signals of (a) and (b) will look
    quite different. The carriers are at different frequencies, and the
    phase of the 9MHz signal is inverted. However, with a double-balanced
    modulator, you will only have the 9 and 11MHz signal so, surprisingly,
    the resulting signals of (a) and (b) will look the same.

    [Note that, in practice, many double-balanced modulators/mixers put
    loads of unwanted signals - mainly due the effects of harmonic mixing.
    However, the basic 'laws of physics' still apply.]

    Finally, although I have spoken with great authority, when I get a
    chance I WILL be doing at test with a tobacco-tin double-balanced mixer,
    a couple of signal generators and a spectrum analyser - just to make
    sure that I'm not talking rubbish. In the meantime, I'm sure that some
    will correct me if I'm wrong.

    Ian.
    --




  13. #43
    DTC
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on an astronomically-lowcarrier frequency

    Jeff Liebermann wrote:
    > Argh, that brings back fond nightmares of Ma Bell.


    And of splicing damaged buried plant in a wet trench...that stuff had a
    bite to it.



  14. #44
    Don Bowey
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency

    On 6/30/07 10:44 PM, in article
    [email protected], "DTC"
    <no_spam@move_along_folks.foob> wrote:

    > Mike Kaliski wrote:
    >> ELF communications are carried out at very slow data rates, only a few
    >> characters per hour at best.

    >
    > Actually its on the order of several characters per minute using a 64
    > character "alphabet".
    >
    >> It is possible to communicate at a base band frequency of 0Hz. This is what
    >> happens when you talk down a hard wired telephone or intercom. At a
    >> telephone exchange (switching centre), the signals from each line are
    >> modulated onto a higher frequency for onward transmission down a trunk wire
    >> cable or fibre optic cable. The multiplexed high frequency modulated signals
    >> are down converted back to audio frequencies once they reach the intended
    >> destination.

    >
    > In the old T carrier (before 24 channel digital T1) carrier, each telephone
    > conversation was modulated onto a low frequency radio frequency AM signal
    > ranging from (and don't quote me as its been over thirty years since I
    > worked T spans) 50 KC to 200 KC. Very similar in principle to the 5 kc wide
    > AM radio station signals on the 530 kHz to 1700 kHz AM broadcast band.


    The O Carrier systems went from a low of about 32 kHz up to 164 kHz if I
    remember right. And the mainstay of long-haul communications (L Carrier)
    channel bank, was 64 - 108 kHz.

    One of the most strange Carrier Systems I worked with was a 1930s vintage H
    Carrier, one channel ssb "system" operating at about 12 kHz, and it ran
    without automatic synchronization. That was in the 60s. We used it as a
    maintenance channel in a voice over data configuration for a gap-filler
    radar site. I've never seen a more extreme merging of old and new
    technologies.

    Don





  15. #45
    Don Bowey
    Guest

    Re: AM electromagnetic waves: 20 KHz modulation frequency on anastronomically-low carrier frequency

    On 6/30/07 11:25 PM, in article [email protected], "John Smith
    I" <[email protected]> wrote:

    > Radium wrote:
    > ...
    >
    > You miss the simple point, the dc is the carrier ... instead of dc, you
    > could put a 1 hz signal on the line and modulate it with your voice,
    > indeed, you can put a 30 hz signal on the line and modulate it with your
    > voice--if you can tollerate a bad 30 hz hum! But, who knows, perhaps
    > you are tone deaf to the 30 hz hum and would like it ...
    >
    > JS


    But you miss the basic point......

    The topic was Amplitude Modulation.




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