A badly tuned/designed super-regenerative receiver can put out a lot of
garbage. For commercial products, the receiver needs FCC approval to
ensure this doesn't happen.
Mike
On 7/5/2012 4:03 PM, ed breya wrote:
The wireless data links in those R/C sensor type things don't operate
near GPS carriers, but their harmonics can land there. The transmitted
power allowed should be too small to interfere with anyone's receiver
farther away - yours is probably pretty close. I believe that the
remote senders do not wait for any polling signals - if so, they would
have to be receiving on a regular basis, taking precious battery life.
It makes more sense for them to just burst transmit at regular
intervals, while the line-powered (or bigger-battery-powered) base
station is always listening, or listens at various intervals to see if
any remotes are calling. That's why it takes a while to get the
initial temperature data when the system starts up.
The base station receivers used for simple, cheap VHF data are
typically super-regenerative type for high sensitivity, so when
they're fired up it may appear that they're transmitting, but actually
are only receiving, with lots of crap kicking out of the super-regen
circuit. A common carrier used for VHF remotes is around 315 MHz - the
fifth harmonic of that one is especially bad, landing almost right on
top of GPS. When you add in the loose frequency stability and
modulation, and the regen signals, the transmitters and receivers can
cause quite a spectral mess.
Ed
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