help me hack mailbox alert
 

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. I can't quite see
the top of that TV antenna from the mailbox.

I'm getting the impression that I should find some way to boost the
transmitter signal. Any way to do this? The transmitter is powered by
2 3V lithium batteries. There's a Radio Shack provided parts list on
the web but I can't make much sense of it.

One thing I might try: Our detached garage is about 75' closer to the
mailbox than our house. The apex of the roof of the garage is probably
in line of sight of the mailbox. There is existing conduit for phone
wire from the garage to the house. I could probably run a long
"antenna" wire from the garage roof apex to the base unit inside the
house, but I wonder if the resistance (oh, right --impedance) of long
wire might throw cold water on this idea.

I know only of smattering of electrionics and certainly not much
analog. Any suggestions appreciated.

--zeb

FIRST: You really ought to rephrase that subject line. :)


As to the mailbox activity whatchamcallit, try putting a proper
directional antenna on the TX unit (the mailbox transmitter.) I vaguely
recall the device. I have no clue what frequency it may use, but I'm
sure someone here will know it. Then wire a directional antenna on the
RX unit (the house side.) You might also try placing the entire
receiver at this garage you speak of, and use a 4 pair cable to the
house to feed the LED, buzzer, and reset signals back to the dwelling.
You will likely have to buffer or isolate these with either transistors
or relay circuits to overcome the loop impedance of the cable, depending
on how fussy the box is.

Even though it might seem so, this is not likely to be too complicated.

Have fun!
Pat

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