Acoustic Telephone Modem for Radio Shacks first computer 1977

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Radio Shack Modem 26-1171

I spotted this 'original still in the box'  first Radio Shack Acoustic Modem while browsing in my computer museum warehouse last week. Not a unique item but worth a little discussion.

Modems were developed to fill the need to connect a printing device to the telephone line. Devices with functions like modems were in use as early as the 1920's however the mass production of modems started in the 1950's. SAGE air-defense systems in 1958 used modems and the word modem to connect there large computers together in a network using telephone lines.

These early modems worked at slow speeds of 110 to 300 bits per second or as computer folks would say "baud" and not "bits per second".  These early modems had a very simple function of converting the tones that could be sent over telephone circuits into digital "One's (1) & Zero's (0).  This allowed two way digital communications over wires for very long distances.

Modems performance did not improve much until the microprocessor was embedded into the circuitry in the late 1970's.  Telephone modems were used by personal computer users & others until the World Wide Web or Internet became common use in the mid to late 1990's. With the use of embedded microprocessors the smart modem speed of data transmission over telephone circuits increased up to 14.4 Kilobits per second. Almost no one uses this type of telephone modems now except for Telephone/FAX machines.  FAX machines are dying out fast with the sending of text document over the Internet.

FAX machines may be in use for a long time as they have a different level of privacy then the Internet - not really private but also not as searchable as the Internet.

The word modem is still in use as a common device used to connect the Internet, DSL or other high speed data  links to computers and other digital devices.
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Radio Shack Modem 26-1171

This Radio Shack Modem has never been out of the box until now - 37 years after it was sold.

Radio Shack Modem 26-1171

This Radio Shack Modem is acoustic coupled to the telephone line and no electrical connection were made direct to the phone line.  The Acoustic coupling was not real efficent because of the extra telephone microphone and telephone ear receiver being coupled to the modem over and air link. The next photo shows this link.
The art deco telephone was also in the museum warehouse - The green color could not have been very popular however I will sure keep as cool example of the old rotary dial up telephone.

Radio Shack Modem 26-1171

Here you see how the telephone was placed into the rubber coupling of the receiver and transmitter on the modem - no electrical connection.  ATT had a monopoly and some government regulations did not permit direct connecting to the telephone line.

Of course many users ignored the regulation and made direct connections for a more efficient data transfer.


I expect Steve Wozniak and Steve Jobs often made direct connection to the telephone line for some of their Blue Box calling to avoid paying the long distance tolls in the early 1970's.. The Steve's has a good little business selling their Blue Box's for short period of time.

Radio Shack Modem 26-1171 Manual 

The Manual was included in the box with modem and had a good description of the device and how it worked along with a schematic diagram.

Modem Manual Full Copy

TRS -80 Radio Shack Model 1 Computer

This Modem is most likely not made by Radio Shack but a private labeling of a general purpose Modem for the TRS- 80 Model 1 computer - the first Radio Shack computer - 1977.

 All the information you would want about Radio Shack from 1939 to 2011

Video of TRS 80 Model 1 advertisement 

Post update 3-17-15-------------------------------------------------------------------------------
This post created a lot of interesting comments and email for me - These brought back  memories for me as I indicated I used the TRS - 80 model 1 for  number of years. Here is a typical email from 

Mark Andrews
"I remember these well. The local RS had one on display with the TRS Model I. I wrote, debugged and ran my first program on that computer in 1977 at the ripe old age of 14. I coded it on pape first, then rode my bike to the store and typed it in. Several debugging cycles later (and about 2 hours) I got it to run. The manager liked the fact that I was there. Shoppers would come in and he would say "Look! It's so easy that a kid can use it!". "
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While in the warehouse finding the Radio Shack Modem I came across these switches -they have been out of sight &  stored for 20 or 30 years.

Looks like the same switch used on the IMSAI 8080 computer and perhaps a few others. If any of you retro computer folks need one please contact me.

Computer front panel switch 

Computer front panel switch

Mostly red and a few black switches about 150 or so.







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David Larsen

It is always fun to look thought the computer museum warehouse. I have more then 10,000 items on the museum data base "Past Perfect". This is not fully complete so their are probably twice this many total items and having been collecting for over 40 years I sure don't remember just what is in the warehouse. 

           .^{"by David Larsen"  KK4WW Computer Collector Historian} 

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