<s>
The	O
Pennywhistle	O
was	O
an	O
early	O
acoustic	B-Device
coupler	I-Device
modem	B-Application
originally	O
designed	O
and	O
built	O
by	O
Lee	O
Felsenstein	O
in	O
1973	O
,	O
and	O
later	O
commercialized	O
and	O
offered	O
for	O
sale	O
in	O
1976	O
.	O
</s>
<s>
It	O
was	O
one	O
of	O
the	O
earliest	O
modems	B-Application
available	O
for	O
hobbyist	O
computer	O
users	O
.	O
</s>
<s>
Like	O
most	O
acoustic	B-Device
coupler	I-Device
modems	B-Application
,	O
the	O
Pennywhistle	O
was	O
replaced	O
by	O
the	O
Hayes	O
Smartmodem	O
and	O
similar	O
models	O
from	O
the	O
early	O
1980s	O
.	O
</s>
<s>
As	O
part	O
of	O
the	O
effort	O
that	O
would	O
lead	O
to	O
the	O
Community	O
Memory	O
bulletin	B-Application
board	I-Application
system	I-Application
,	O
Lee	O
Felsenstein	O
had	O
found	O
an	O
Omnitech	O
modem	B-Application
(	O
"	O
or	O
something	O
like	O
that	O
"	O
)	O
.	O
</s>
<s>
Designed	O
to	O
operate	O
at	O
rates	O
as	O
high	O
as	O
300bits	O
per	O
second	O
(	O
bit/s	O
)	O
,	O
the	O
modem	B-Application
was	O
able	O
to	O
change	O
its	O
speed	O
to	O
match	O
conditions	O
or	O
differences	O
in	O
the	O
modems	B-Application
at	O
either	O
end	O
.	O
</s>
<s>
The	O
modem	B-Application
was	O
attached	O
to	O
a	O
Teletype	B-Application
Model	I-Application
33	I-Application
ASR	O
machine	O
at	O
Leopold	O
's	O
Records	O
in	O
Berkeley	O
,	O
California	O
and	O
connected	O
to	O
the	O
SDS	B-Device
940	I-Device
mainframe	B-Architecture
computer	I-Architecture
in	O
San	O
Francisco	O
.	O
</s>
<s>
These	O
improvements	O
meant	O
the	O
modem	B-Application
was	O
able	O
to	O
follow	O
changes	O
in	O
the	O
reference	O
tone	O
no	O
matter	O
what	O
the	O
source	O
of	O
that	O
drifting	O
was	O
,	O
local	O
or	O
remote	O
.	O
</s>
<s>
Felsenstein	O
had	O
been	O
talking	O
about	O
building	O
a	O
design	O
for	O
a	O
data	B-General_Concept
terminal	I-General_Concept
he	O
called	O
the	O
Tom	B-Device
Swift	I-Device
Terminal	I-Device
,	O
but	O
the	O
design	O
was	O
n't	O
ready	O
for	O
development	O
.	O
</s>
<s>
Felsenstein	O
then	O
asked	O
if	O
Spergel	O
would	O
be	O
interested	O
in	O
a	O
related	O
project	O
,	O
a	O
modem	B-Application
that	O
he	O
had	O
previously	O
designed	O
.	O
</s>
<s>
Spergel	O
was	O
able	O
to	O
cobble	O
together	O
a	O
version	O
of	O
the	O
modem	B-Application
for	O
a	O
price	O
of	O
$109	O
.	O
</s>
<s>
The	O
two	O
then	O
sent	O
a	O
copy	O
of	O
the	O
schematics	B-Application
to	O
Les	O
Solomon	O
at	O
Popular	O
Electronics	O
magazine	O
,	O
where	O
it	O
was	O
featured	O
on	O
the	O
cover	O
of	O
its	O
March	O
1976	O
issue	O
.	O
</s>
<s>
Like	O
other	O
acoustic	O
coupled	O
modems	B-Application
,	O
the	O
Pennywhistle	O
design	O
was	O
dominated	O
by	O
the	O
two	O
large	O
rubber	O
cups	O
on	O
the	O
top	O
of	O
the	O
device	O
that	O
were	O
used	O
to	O
hold	O
the	O
handset	O
of	O
a	O
standard	O
Western	O
Electric	O
phone	O
.	O
</s>
