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AM transmitter question

Discussion in 'General Electronics' started by Eric Sears, Jan 6, 2005.

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  1. Eric Sears

    Eric Sears Guest

    Hi
    Just a brief comment - you MAY still have a drift problem; or perhaps
    I should say "hand capacity" problem - which is shifting the
    frequency of the transmitter when you are touching the aerial.
    You may need to try tuning receiver when you are NOT touching the
    aerial.
    If that doesn't help, you could use a "counterpoise" in place of an
    earth - ie connect an 8 foot wire to the earth side of the circuit and
    drape it along the floor (this will probably mean just connecting it
    the the -ve side of the battery).

    Something else that may help is to use the HIGH end of the band (near
    1500 kHz) - the short aerial will be more efficient.

    Otherwise simply use 20 feet of wire for an aerial as high around the
    wall in the room as possible. (Very THIN wire will be fine).

    It is also possible that the polarisation is incorrect. Try turning
    the radio so that the rod aerial is vertical. It may be that when you
    touch the aerial you are adding a horizontal component to the
    transmission.

    Well that's enough to try!

    Eric (ZL2BMI)
     
  2. Eric Sears

    Eric Sears Guest

    AFTERTHOUGHT!
    Make sure you are tuned to the fundemental frequency!
    I have built many trasmitters in my time - and often you may actually
    be tuned to a weak harmonic. Tune up and down the band with the
    receiver only a few feet away from the TX - and make sure you are
    listening to the strongest signal.
     
  3. Good Music

    Good Music Guest

    Help,

    I've purchased a pre-assembled inexpensive AM radio transmitter, connected
    directly to an 8-foot whip antenna, and find that as long as I'm touching
    the antenna, i can pick up music from the CD player through my radios fine.
    But when I let go of the antenna, the sound goes away almost completely.

    The manual says I can put certain values of inductors in series with the
    whip antenna lead to "improve performance" but I have no idea if that has
    anything to do with fixing the problem of the antenna only working when I'm
    holding it.

    The andtenna is 8 feet long oriented vertically, and the readios are about 8
    feet from the antenna. This is to be used as a household broadcaster (only
    need a range of about 30 feet).

    This is the transmitter: I've read many don't like it because it drifts but
    that's not the issue for me, it's just getting it to work at all, I think I
    might still have this problem if I bought the more expensive AM transmitter
    with microprocessor to prevent drifting:
    http://www.hobbytron.com/R-AM-1.html

    Thanks greatly for suggestions on how to correct this problem.

    - Goodmusic
     
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