In that case a compressed air spud gun could probably have enough range
to cover the area. That makes it cheaper to run multiple launches in an
afternoon, since any one hunt shouldn't take more than 15 minutes to
20 minutes.
With a 40 acre parcel you're not talking about long distances - less than
half a mile maximum, or a quarter mile if you start in the center. It doesn't
take much power to cover that distance: a simple overtone crystal
oscillator and perhaps a one-stage amplifier is sufficient. That is quite
easy to build yourself - you can have several spares (in case one doesn't
survive the landing) for the cost of a commercial unit. Here is one example,
though it probably is more complex than necessary:
http://home.att.net/~jleggio/projects/rdf/40mw_tx.htmI've used the 9th overtone of a 16 MHz crystal successfully in such a
circuit. You can also operate the crystal on the fundamental (or a
lower overtone) and extract the desired harmonic through a filter. There
is a whole range of computer baud rate crystals that multiply up to
147.456 MHz that are commonly available and work well for this (such as
18.432 MHz, 16.384 MHz, 12.288 MHz, 8.192 MHz, etc.) You can also get
canned crystal oscillators that run off 5V or 3.3V on either a subharmonic
(so you extract the desired frequency with a tuned circuit) or specially
programmed for your desired frequency. For example, a 49.14 MHz oscillator
from Mouser that multiplies to 147.42 is available off the shelf for under
$5, and you can get one programmed to your desired frequency (though
you may have to settle for 1/3 of the desired output, since many parts
are limited to 50 or 70 MHz) for another dollar or two.
Ramsey Electronics used to sell a 2m "wireless mic" kit that was about
1" x 2" and contained a crystal-controlled transmitter. We used a number
of these for low power hidden transmitters - including a dozen or more
hidden around a school yard on different frequencies. Maximum range
was perhaps 100', but could be extended with a better antenna and/or
a simple transistor amplifier. (And if the signal is very weak, that is even
better training for locating a real ELT!)
I've got a set of the 30mW 2m MicroHunt transmitters and they work great
over areas that size (and larger). But for aerial launching and the resulting
potential impact, I'd consider something a bit more expendable.