The
Surface Acoustic Wave filter is an
electro mechanical
filter. It consists of a
crystal with
electrodes connected
to it.
Input
connectors
-----. .----
_|_ _|_
.----------------.
`----------------'
"T" "T"
-----' crystal `----
output
connectors
When a signal of a 'pass through' frequency is connected
to the input, it causes the
crystal to
expand or
contract
(but offcause only a
microscopic change. This effect is
called piezoelectrics). The
wave created by this
travles
trough the
crystal and create an
electric signal on the
output.
By altering the
shape of the
crystal and trimming it down with
a
laser cuter, a
highly complex filter can be
created.
The SAW filter is a small solution to a
complex filter device,
but it
attenuates the
signal with about 30 dB at it's
peak
pass-
trough. This means the
output signal must be
amplified
before use.