RF sonde, pulse generator

I would like to make a sonde for tracing pipes. If your not sure what a sonde is basicly it is a Rf transmitter that a receiver pick up you put it inside a buried pipe than run the receiver over the ground untill you get the strongest signal. I can build a pulse generator using a 555 timer and pick it up on the receiver but can i make the signal stronger, putting my hand between the generator and the receiver block the signal i need it to go through several feet of dirt. it also need to be small
Can someone help me.
Thanks

Dirt especially wet dirt can be a real problem to get through.

The next question is what the pipe type is

As an overly generalized point you often try to go for as low a frequency as possible.

When you say small how small do you mean?

One way to do it is to say make a coil around a largish lump of ferrite (reverse of an AM radio) and use that to couple into the surroundings such as the pipe or the medium it is carrying.

There is the problem of "optimum" frequency, one way to do this is to sweep across a broad frequency band at a regular interval, your receiver likewise scans across and syncs to the frequency sweep, thus you can get some indication of changes of soil condition etc (ie if there is a leak or plant roots etc etc).

It's been a good few years (mid 80s cave radios) that I did work on this sort of thing so I'm not sure if there are any good refrences out there these days.[COLOR="Silver"]

---------- Post added at 10:24 ---------- Previous post was at 10:23 ----------

Ok here is a thought.

If you look at some of the ferrite rings available for EMI filters in mains leads thay are designed to slip over quite thick cables and are thus realy short sections of thin walled tube.

If you use button cells as your power source you can quite easilly find those to fit snugly inside of one of these ferrite tubes along with spring clips to act as a battery holder.

You can design another ferrite tube to hold a surface mount PIC and a couple of power fets etc to provide a 1KHz shaped waveform (think walsh generator and additive currents).

Find a ferrite bobbin with a hollow core and end plates that are the same or slightly smaller diameter as the outside diameter of the ferrite tubes. Wind your radiating coil around this bobbin using fine wire and add a cpacitance to make it aproximatly resonate at 1KHz when constructed.

Now if you glue the battery holding tube on one side of the bobbin and the surface mount generator tube on the other side of the bobbin and pass the wires through the bobbin as required you have in effect a resonant ferrite antenna at 1KHz with all the gubins inside the ferrite arms.

With a bit of skill and luck the whole thing could be made a little under 1cm diameter and 3cm long with off the shelf components.