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Posers and Puzzles

Posers and Puzzles

  1. Subscriber sonhouse
    Fast and Curious
    02 Aug '06 23:38 / 2 edits
    Here is one for you radio freaks out there:
    In a warzone, the battle commander has to communicate with his captains in the field. For some unknown reason, the radios they use which usually work fine, all of them only transmit FM (they can transmit and receive AM, FM, SSB and CW (morse code) when they work right) However for some reason or other they can only transmit in FM but receive only AM. They tune fine, the units transmit the normal amount of power which usually results in fine communications links. So how does the field radio expert fix or bandaid the problem and allow them to communicate. They don't have the time to send the radios to the depot level maintenance station, they need to communicate NOW.
  2. 02 Aug '06 23:55
    Originally posted by sonhouse
    Here is one for you radio freaks out there:
    In a warzone, the battle commaner has to communicate with his captains in the field. For some unknown reason, the radios they use which usually work fine, all of them only transmit FM (they can transmit and receive AM, FM, SSB and CW (morse code) when they work right) However for some reason or other they can onl ...[text shortened]... e time to send the radios to the depot level maintenance station, they need to communidate NOW.
  3. 03 Aug '06 10:27 / 1 edit
    They talk face to face instead?

    Edit, or an equally silly answer, which i think is probably at least on the right track
  4. Subscriber sonhouse
    Fast and Curious
    03 Aug '06 11:39
    Originally posted by mazziewag
    They talk face to face instead?

    Edit, or an equally silly answer, which i think is probably at least on the right track
    No, they are hundreds of Km apart. It needs an electronic solution.
  5. 03 Aug '06 13:32
    they could just use them like walkie talkies stay on AM until you want to broadcast then switch when you are done switch back.
  6. Standard member JYD
    03 Aug '06 17:11
    Don't know if this is possible but how about sending morse over the fm, would the am pick that up?
  7. Subscriber sonhouse
    Fast and Curious
    03 Aug '06 21:32
    Originally posted by aginis
    they could just use them like walkie talkies stay on AM until you want to broadcast then switch when you are done switch back.
    That won't work because they can only transmit FM, no matter how you use it. Normally FM cannot be decoded by an AM reciever. So How do they communicate?
  8. 03 Aug '06 22:10
    Originally posted by sonhouse
    That won't work because they can only transmit FM, no matter how you use it. Normally FM cannot be decoded by an AM reciever. So How do they communicate?
    That;s true, but FM stereo uses 2 channels, one in FM mode and the other in AM. But military standards doen't contemplate stereo sound transmissions
  9. Subscriber sonhouse
    Fast and Curious
    04 Aug '06 02:18 / 1 edit
    Originally posted by JYD
    Don't know if this is possible but how about sending morse over the fm, would the am pick that up?
    That might work. The problem with that I think, is it would be basically a on and off noise signal but it could work, slowly, compared to voice. But there is a better way. The very first communications by radio was essentially a noisy morse code and the transmitter a rotating spark generator that produced radio waves of such a high bandwidth it would be heard in just about any radio ever made! At the time they had these really wierd detectors that worked after a fashion. I never heard that stuff but it must have been an on and off noise signal. Thats basically what you would hear in that circumstance. One problem with that is in the military theater they have basically given up on morse code and there is not many people can still use it. Probalby have to sequester some hams if they could find a few! 5 points for a good effort! But like I say there is a better way.
  10. Subscriber sonhouse
    Fast and Curious
    04 Aug '06 02:21 / 1 edit
    Originally posted by CrazyLilTing
    That;s true, but FM stereo uses 2 channels, one in FM mode and the other in AM. But military standards doen't contemplate stereo sound transmissions
    FM stereo has no am in it at all. If you are interested, here is a quicky 50 cent tour of the subject. Its three fm signals multiplexed together.
    One for FM mono and two next to it with their own frequency band in which two fm signals are sitting side by side with a 19 KHz separation from the mono to the stereo and a 38 Khz separation between each stereo chanell. Its a complex scheme to allow old radios and newer ones (make that every radio made since 1970!) both get a signal. Anyway here is a link to study it:
    http://www.st-andrews.ac.uk/~www_pa/Scots_Guide/RadCom/part21/page1.html
  11. Standard member XanthosNZ
    Cancerous Bus Crash
    04 Aug '06 02:39
    Imagine each reciever/transmitter as a black box.

    Each black box can only recieve AM and can only output FM.

    Now if we take a black box and turn it inside out (invert it in electronic terms) we have something that can take FM input and only output AM. So now if we connect our inverted black box to a non-inverted black box we have something that recieves FM and transmits FM (with a transfer between the boxes in either AM or sound).

    If each person carries this combination instead of a single radio we can communicate on the FM band without any problems.
  12. Subscriber sonhouse
    Fast and Curious
    04 Aug '06 05:11
    Originally posted by XanthosNZ
    Imagine each reciever/transmitter as a black box.

    Each black box can only recieve AM and can only output FM.

    Now if we take a black box and turn it inside out (invert it in electronic terms) we have something that can take FM input and only output AM. So now if we connect our inverted black box to a non-inverted black box we have something that rec ...[text shortened]... is combination instead of a single radio we can communicate on the FM band without any problems.
    That would undoubtedly work, but remember the military, they have SUCH a limited budget and no time. They have to use the radios on hand. There is a simple way.
  13. 05 Aug '06 21:19
    Are we assuming that the carrier is the same for each transmission type? This is unusual as the bandwidths required by each are different. That is true at least for commercial applications, but I'm not too sure about military applications (where communications density would not be a big problem).
  14. Subscriber sonhouse
    Fast and Curious
    06 Aug '06 03:24
    Originally posted by Gastel
    Are we assuming that the carrier is the same for each transmission type? This is unusual as the bandwidths required by each are different. That is true at least for commercial applications, but I'm not too sure about military applications (where communications density would not be a big problem).
    The carrier for FM is just that, a moving carrier, moving in frequency of course. It still generates sidebands but not like AM. AM sidebands are directly related to the modulation frequency. In amateur and military communications, both FM and AM are about the same bandwidth, FM swinging between two frequency extremes and AM producing sidebands twice the bandwidth of the modulation, thats why single sideband modulation is more efficient, half the bandwidth of AM and because of that the resultant path gets an 8 db free boost, almost like making an am transmitter 10 times stonger, so what you can do with a thousand watts of AM power, you can do with 100 watts of SSB.
    Broadcast FM bandwidth is about 175 Kilohertz wide but ham and military limits that frequency excursion to about 3 kilohertz because you only need to hear 3 khz of audio to understand voice. So it takes up less bandwidth than AM which for a 3 Khz audio signal needs 6 Khz of bandwidth. Thats why SSB is twice as efficient bandwidth wise. But there is a solution to an AM reciever listening to an FM broadcast.