On 25 jul, 20:23, " wrote:
We've been having trouble with bicycle thieves in my neighborhood. I'd
like to set up a "bait-bike" that includes a low-power pulse beacon AM
transmitter inside the frame and ***no visible*** antenna outside the
frame. I'd like to have approximately 1-mile range. I've built a
couple of Ramsey kits, but don't have much expertise.
- I'd appreciate any recommendations for a transmitter circuit.
- Will the frame perform as an adequate antenna?
- How about a dipole made from insulated wire taped to the exterior of
the frame?


Hello,

When you mean "AM broadcast band" with AM, you will very likely not
get it working. You will not be able to make a concealed efficient
antenna and noise level is that high, that you will never receive the
signal at one mile distance.

The antenna is the (most) difficult part. I would recommend you to go
to VHF (as Richard suggested). You can use the bicycle frame as ground
(counterpoise). You could insulate some metallic parts of the bicycle
(Rack, Fender, mudguard) and use that as an antenna. Make sure that
you don't compromise safety when modifying bicycles. The antenna
impedance will be reasonable so you can probably use a simple matching
network.

Because of the short(er) wavelength you can have some directivity in
the receiving antenna also, this helps to trace your "bait". "Bait-
bicycles" are frequently used by the Police.

When this is a non-commercial project, you may seek advice from the
Radio Amateur Community (in fact you did via this posting). Also don't
forget the legal aspects of radio frequency use.

Best regards,

Wim
PA3DJS
www.tetech.nl
the mail is OK when you remove abc