On Mon, 21 Mar 2005 09:25:03 -0600, "Bob Shuman"
wrote:


I would think that the collar based receiver might emit the 17Khz tone when
the animal wearing it strays beyond the RF transmitter's range.

Hi Bob,

The 17 khz frequency sounds a little odd to me also. But, there is
some literature on the website that indicates that's the frequency of
the transmitter.

I have a few ideas regarding WHY they use such a low
frequency...........

First, they probably have experience at vlf. There are other models
that use buried wire to define the dogs limits in travel. You can bury
an antenna at these lower frequencies, which is why they are used for
navigation and communication with submerged submarines.

But, obviously, the range has to be very limited because the thing
doesn't have an external antenna. Even if it did, the antenna would be
a poor radiator because the antenna is so short relative to the
wavelength.

Also, direct conversion receivers at these low frequencies are very
easy to build, a single transistor and a diode detector is easy to
build and cheap.

If I was designing the thing, I'd use 433 Mhz, where simple and low
cost data receiver and transmitter chips are available and do not use
much power from the battery.

Check out the schematic, there are 3 chips that feed different
windings on a transformer and the time constants in the schematic
don't make sense for transmitters in the MHZ and higher range.

Regards,

Al