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?

On Fri, 25 Jul 2008 11:23:55 -0700 (PDT), "
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?

No.

- How about a dipole made from insulated wire taped to the exterior of
the frame?

Equally unlikely.

If you have built Ramsey kits for AM transmitters, you should be well
aware that they rarely transmit more than a block for the suggested,
large (relatively speaking, of course) antenna. Putting something
smaller, inside the frame is like trying to yell through a straw.

Look for an FM transmitter kit. The antenna can be the frame and a
wire wrapped around what looks like one of those kid's fiberglass
whips for a flag. The whip only has to be a meter long at most.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Fri, 25 Jul 2008 11:23:55 -0700 (PDT), "
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?

No.

- How about a dipole made from insulated wire taped to the exterior of
the frame?

Equally unlikely.

If you have built Ramsey kits for AM transmitters, you should be well
aware that they rarely transmit more than a block for the suggested,
large (relatively speaking, of course) antenna. Putting something
smaller, inside the frame is like trying to yell through a straw.

Look for an FM transmitter kit. The antenna can be the frame and a
wire wrapped around what looks like one of those kid's fiberglass
whips for a flag. The whip only has to be a meter long at most.

73's
Richard Clark, KB7QHC

Alternatively, Petco has an electric fence kit that could be attached to
the frame. :-)

ac6xg

Jim Kelley wrote:
Richard Clark wrote:
On Fri, 25 Jul 2008 11:23:55 -0700 (PDT), "
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?

No.

- How about a dipole made from insulated wire taped to the exterior of
the frame?

Equally unlikely.

If you have built Ramsey kits for AM transmitters, you should be well
aware that they rarely transmit more than a block for the suggested,
large (relatively speaking, of course) antenna. Putting something
smaller, inside the frame is like trying to yell through a straw.

Look for an FM transmitter kit. The antenna can be the frame and a
wire wrapped around what looks like one of those kid's fiberglass
whips for a flag. The whip only has to be a meter long at most.

73's
Richard Clark, KB7QHC

Alternatively, Petco has an electric fence kit that could be attached to
the frame. :-)

ac6xg

Put gentian violet powder on the hand grips, then look for purple hands
on the thieves.

wrote:
- Will the frame perform as an adequate antenna?

What would you use for the counterpoise?
--
73, Cecil http://www.w5dxp.com

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

"Jim Kelley" wrote in message
...
Richard Clark wrote:
On Fri, 25 Jul 2008 11:23:55 -0700 (PDT), "
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?

No.

- How about a dipole made from insulated wire taped to the exterior of
the frame?

Equally unlikely.

If you have built Ramsey kits for AM transmitters, you should be well
aware that they rarely transmit more than a block for the suggested,
large (relatively speaking, of course) antenna. Putting something
smaller, inside the frame is like trying to yell through a straw.

Look for an FM transmitter kit. The antenna can be the frame and a
wire wrapped around what looks like one of those kid's fiberglass
whips for a flag. The whip only has to be a meter long at most.

73's
Richard Clark, KB7QHC

Alternatively, Petco has an electric fence kit that could be attached to
the frame. :-)

ac6xg


You're a man after my own heart, ac6xg. 8)

Jack

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?

You would need an LC (inductance/capacitance) loading circuit to
resonate the frame as a 1/2 wave "antenna" before it would even be
possible to work (heck, I have never really thought about it before, but
resonating it, the frame, at a full wavelength might even be better!)

I have actually heard of people, successfully, using a 1/2 radiator with
no counterpoise--with good results. In your idea/plan, this might just
be the best go ...

A mile range? That would require power which might be difficult to
provide with batteries and for an extended length of time ... where
would you hide those batteries? In the handlebars?

Regards,
JS

Wimpie wrote:

...
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
...
Best regards,

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


I concur, perhaps a cheap FM xmitter in the range of 88-108mc. The
frame should serve as a good 1/2 wave antenna for this frequency and the
plans for such an xmitter are readily available--a search of the net
will provide you with multiple options ...

Regards,
JS

Another solution could be APRS or something similar. There are
separate transmitters small enough to fit in a 1.5 - 2.0" tube,
encluding a battery. Antenna(s) in the seat, frame as the
counterpoise? RF burns? Oh, yeah, sure. But who cares, right? All
normal stipulations apply.
- 'Doc