<s>
The	O
Foster	B-Device
–	I-Device
Seeley	I-Device
discriminator	I-Device
is	O
a	O
common	O
type	O
of	O
FM	B-Application
detector	B-Algorithm
circuit	I-Algorithm
,	O
invented	O
in	O
1936	O
by	O
Dudley	O
E	O
.	O
Foster	O
and	O
Stuart	O
William	O
Seeley	O
.	O
</s>
<s>
The	O
Foster	B-Device
–	I-Device
Seeley	I-Device
discriminator	I-Device
was	O
envisioned	O
for	O
automatic	O
frequency	O
control	O
of	O
receivers	O
,	O
but	O
also	O
found	O
application	O
in	O
demodulating	O
an	O
FM	B-Application
signal	O
.	O
</s>
<s>
The	O
Foster	B-Device
–	I-Device
Seeley	I-Device
discriminator	I-Device
uses	O
a	O
tuned	O
RF	O
transformer	O
to	O
convert	O
frequency	O
changes	O
into	O
amplitude	O
changes	O
.	O
</s>
<s>
A	O
transformer	O
,	O
tuned	O
to	O
the	O
carrier	O
frequency	O
,	O
is	O
connected	O
to	O
two	O
rectifier	B-Algorithm
diodes	O
.	O
</s>
<s>
The	O
circuit	O
resembles	O
a	O
full-wave	O
bridge	O
rectifier	B-Algorithm
.	O
</s>
<s>
Foster	B-Device
–	I-Device
Seeley	I-Device
discriminators	I-Device
are	O
sensitive	O
to	O
both	O
frequency	O
and	O
amplitude	O
variations	O
,	O
unlike	O
some	O
detectors	B-Algorithm
.	O
</s>
<s>
Therefore	O
a	O
limiter	O
amplifier	O
stage	O
must	O
be	O
used	O
before	O
the	O
detector	B-Algorithm
,	O
to	O
remove	O
amplitude	O
variations	O
in	O
the	O
signal	O
which	O
would	O
be	O
detected	O
as	O
noise	O
.	O
</s>
<s>
Other	O
types	O
of	O
FM	B-Application
detectors	B-Algorithm
are	O
:	O
</s>
