I thought I just put an update here for posterity. I got it working.

wrote:
Hi, I'd like to extend the operable range of a Radio Shack cat #
63-1110 mailbox alert. It works with a small photo sensitive
transmitter mounted inside the mailbox. When the mailbox is opened
(i.e. a change of light level) the transmitter sends a burst (of what
frequency I know not) to the base unit. The indoor wall-wart-powered
base unit with a 11" antenna flashes an LED and beeps when it
receives
this signal.

The directions say the transmitter should be max 150' away and in
line
of sight. Well, I'd like the thing to work at 275' and slightly out
of
line of sight --around some trees and over a small hill.

I tried hooking the base unit antenna to the center wire of coax that
goes to our rooftop TV antenna but that didn't work.

It turns out that particular coax feed from the TV antenna is broken or
something. The antenna line was put in by the prior owner and I just
assumed it worked. Later, I tested by hooking directly to an old TV
and found it does NOT work.

Another room in the house has a working TV antenna connection, and this
is the one I'm now using.

Here's the steps I took.

1) Opened the receiver case and removed the original antenna.
2) Reamed a round hole in the case to take a solder lug coax terminal.
3) Installed the coax terminal: Soldered the antenna wire to the
solder lug for the center coax conductor. Soldered one end of a 20
gauge wire to the ground plane of the recevier. Wrapped the other end
around the shell of the coax terminal. (They probably make coax
terminals with two lugs but that was
not in my parts bin.) Tightened a coax nut around the wrapped portion.
4) Closed the case. Tested.

I found out from the FCC web site that the transmitter uses 315MHz, so
that's within the range of frequencies TV antennas must grab. We're
out in the mountains. Our TV antenna looks very directional, so I made
sure to point it at the mailbox to maximize reception. We are using
satelite TV now, so at least we can use the old antenna for something.

It works, but I've yet to see how dependable this is. Will post again
if warranted. I have an old Radio Shack UHF/VHF/FM amplifier kicking
around and
could always put it on in case the signal is still too weak.

--zeb