simple tracking transmitter help

Discussion in 'Wireless & RF Design' started by markosillypig, Jan 5, 2015.

  1. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
    184
    0
    hi ever one
    i am looking to make a transmitter that i can here on LW MW or FM just to recive a bleeping signal over a distance of about 30 meters on ground.
    all i want is a simple transmitter i can use to alert me to a rat trap i have made so when a rat gets trapped it will allert me so i can go and let it out somewhere else.
    i have made both of these schematics but they never worked for me
    any ideas please
     
  2. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
    184
    0
    would circuit 2 work with the 2n3904
     
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    What didn't work?
    What kind of receiver were you using?
     
  4. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
    184
    0
    scanner on 2 meters band and both transmitters did not work
     
    Last edited: Jan 6, 2015
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Thats because if those oscillators were oscillating, you would have to tune to the frequency marked on the crystal, +- a few kHz. The circuit you posted called for a 3rd overtone crystal, so it would likely be somewhere between 30 and 80Mhz; not 145! You might be able to hear the third harmonic of 49MHz at 147MHz, but the range would be greatly reduced compared to what you could get at 49MHz.
     
  6. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
    184
    0
    is there a simpler circuit you could recomend.
    as i stated i only want a bleeping or ticking signal to my hand held scanner that would work ?
    i know i could use a 433mhz door bell bought on ebay but it defeats my project of making my own
    cheers
    ps a guy in uk makes these
    http://arbtronics.co.uk/wp/tracking-transmitter/
    so what frequency would it be recived at ?
     
    Last edited: Jan 6, 2015
  7. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    Quite a few scanners receive 30-54MHz. Does yours?
     
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    I'm guessing that the 144 in the model designation means it is on 144MHz. If so, then that crystal is a 7th or 9th overtone crystal, so the oscillator runs at that frequency.

    I have worked with animal tracking collars, and AFAICR, they operated at ~42Mhz, consistent with the 49MHz 3rd overtone crystal mentioned in one of your posted circuits. It is all about the crystal. 140MHz crystals tend to be hard to obtain, expensive, and very fragile.

    Have you searched DigiKey and the like to see if there is a stock crystal available near your desired frequency?
     
  9. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
    184
    0
    tes it does
    28.0-29.695 5 FM 10 Meter
    Amateur Band
    29.7-49.995 5 FM VHF Low Band
     
  10. MikeML

    AAC Fanatic!

    Oct 2, 2009
    5,450
    1,066
    So try the first circuit you posted again with a ~40 to 50MHz 3rd overtone crystal. I have a shoe box full of such crystals from back in the day when two-meter radios were crystal controlled. I would be happy to give you several, but you will have to come to AZ...
     
  11. markosillypig

    Thread Starter Active Member

    Jul 21, 2008
    184
    0
    got some from farnell thanks and AZ a little too far for a weekend trip lol thanks
     
Loading...