Pennywhistle modem
The Pennywhistle was an early acoustic coupler modem originally designed and built by Lee Felsenstein in 1973, and later commercialized and offered for sale in 1976. It was one of the earliest modems available for hobbyist computer users.[1] Like most acoustic coupler modems, the Pennywhistle was replaced by the Hayes Smartmodem and similar models from the early 1980s.
History
Prior modem
As part of the effort that would lead to the
New design
Felsenstein was unimpressed by the Omnitech design, especially its price of $300,[2] and convinced himself he could design a better version. He found that one half of the design problem was easy; generating the proper tones for transmission was simple. The other half of the problem was much harder; listening to the incoming signal and discriminating between the tones for "one" and "zero". The traditional solution was to generate a local reference tone and compare it to the incoming signal, but this was subject to many problems, from noise or distortion on the line, to drifting of the local tone due to events as mundane as temperature changes.[3]
Felsenstein found two key improvements that led to a dramatically less expensive and more reliable design. The first was to ignore the idea of a variable
These improvements meant the modem was able to follow changes in the reference tone no matter what the source of that drifting was, local or remote. It also eliminated the need for a local tunable oscillator, reducing the price of the system.
Commercialization
In 1976, Felsenstein was visiting "the junk man", Marty Spergel of M&R Electronics. Felsenstein had been talking about building a design for a
The two then sent a copy of the schematics to Les Solomon at Popular Electronics magazine, where it was featured on the cover of its March 1976 issue.[5] M&R offered the Pennywhistle in kit form for $129.95, or fully assembled for $225. It was offered for sale for several years.[6] For comparison, the Novation CAT was listed at $179 in 1981 after several years of falling electronics prices.[7]
Description
Like other acoustic coupled modems, the Pennywhistle design was dominated by the two large rubber cups on the top of the device that were used to hold the handset of a standard Western Electric phone. The Pennywhistle had a "step" cut into the front of the case where the various control switches were located, and the RS-232 port projected directly out of the front of the case.
References
Notes
- ^ Roy Allan, "A History of the Personal Computer: The People and the Technology", Allan Publishing, 2001, pg. 17
- ^ a b c Crosby, "ON LINE AT LEOPOLD'S"
- ^ a b c Crosby, "PENNYWHISTLE MODEM"
- ^ Steven Levy, "Hackers", O'Reilly Media, 2010, pg. 220
- ^ Les Solomon, "Solomon's History", InfoWorld, 15 Oct 1984, pg. 55
- ^ William Hawkins, "Computer add-ons", Popular Science, May 1978, pg. 68
- ^ See ComputerMart advertisement, InfoWorld. 31 March 1980, pg. 12
Bibliography
- Kip Crosby, "From Vacuum Tube Flip-Flops to the Singing Altair, an Interview with Lee Felsenstein", The Analytical Engine, Volume 3 Number 1, (November 1995)