UHF Crystal Radio

Discussion in 'Wireless & RF Design' started by vu2nan, Dec 26, 2015.

  1. vu2nan

    Thread Starter Member

    Sep 11, 2014
    43
    10
    UHF Crystal Radio

    A crystal radio was wired up to check whether it could receive VHF/UHF signals in the vicinity of the shack.

    [​IMG]
    VHF / UHF Crystal Radio - Schematic

    No signals were audible, either in the shack or on the shack roof, using a 500 mm whip antenna.

    However, a weak digital signal was detected with the sound powered phones, while moving on the shack roof using a 250 mm whip. Position on the roof and direction in which the whip was pointed were quite critical.

    It was presumed that the signals were from a nearby cellphone tower. A 3 Element Yagi Beam for 33 cm was made using a broken snare drum stick for the boom and 20 SWG bare copper wire for the elements.

    [​IMG]
    UHF Crystal Radio on Yagi Beam - Schematic

    The coil was wound integral with the driven element. The same germanium diode and tubular ceramic capacitor were used.

    [​IMG]
    UHF Crystal Radio on Yagi Beam

    The signal was much stronger with this setup..

    Regards,

    Nandu.
     
    Last edited: Jan 6, 2016
  2. Ramussons

    Active Member

    May 3, 2013
    557
    92
    The "Crystal" radios can be used only for receiving a simple AM signal. AM on VHF and above is RARE and definitely not on UHF.
    What are you trying to pickup?
     
  3. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    congratulawtions, you have discovered the field strength meter.
     
  4. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
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    actually crystal radios can be used to listen to fm, but wide band fm broadcast, by tuning off center (slope detection) narrow band fm has too little deviation, the tuned circuits have to have very high "Q" to get anything.
     
  5. Ramussons

    Active Member

    May 3, 2013
    557
    92
    AM Digital o_O:rolleyes:
     
  6. nerdegutta

    Moderator

    Dec 15, 2009
    2,516
    785
    Cell phone frequency...?
     
  7. Ramussons

    Active Member

    May 3, 2013
    557
    92
    Can someone please educate me on AM at that frequency?
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
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    am at 900 mhz, probably a remote control, or something similar. quite a few simple transmitter/reciever pairs use am because they also use regenerative recievers, which dont respond well to fm. an fm radio (88-108 mhz) cavity is not very large, a metal coffee can has been used before for that. a;lsp,, an lc circuit should have enough Q if you use thick wire, around #12 or so.
     
  9. KL7AJ

    AAC Fanatic!

    Nov 4, 2008
    2,040
    287
    Achhh...I can build one with a garbage can and some coat hangers. HI!
     
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