75A-4 and KWS-1

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The Collins 75A-4 amateur radio receiver Collins 75A-4 Peoria.jpg
The Collins 75A-4 amateur radio receiver

The 74A4 and KWS-1 is an amateur radio receiver and transmitter pair made by the Collins Radio Company of Cedar Rapids, Iowa that were introduced in 1955. They were designed to operate using the then new single-sideband (SSB) voice modulation as well as CW and AM modes. They were influential in popularizing SSB. [1] The KWS-1 transmitter along with the 75A-4 receiver, together, cost over $2500 when new (equivalent to over $20,000 in 2012 dollars). Collins products at the time were considered 'top of the line'. Ham radio enthusiasts nicknamed the pair "The Gold Dust Twins," as they were unaffordable to most amateur radio enthusiasts when first introduced. [2]

Amateur radio use of designated radio frequency spectra for purposes of non-commercial exchange of messages

Amateur radio, also known as ham radio, describes the use of radio frequency spectrum for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation, radiosport, contesting, and emergency communication. The term "amateur" is used to specify "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest;" and to differentiate it from commercial broadcasting, public safety, or professional two-way radio services.

Cedar Rapids, Iowa City in Iowa, United States

Cedar Rapids is the second-largest city in Iowa and is the county seat of Linn County. The city lies on both banks of the Cedar River, 20 miles (32 km) north of Iowa City and 100 miles (160 km) northeast of Des Moines, the state's capital and largest city. It is a part of the Cedar Rapids/Iowa City Corridor of Linn, Benton, Cedar, Jones, Johnson, and Washington counties.

Single-sideband modulation refinement of amplitude modulation

In radio communications, single-sideband modulation (SSB) or single-sideband suppressed-carrier modulation (SSB-SC) is a type of modulation, used to transmit information, such as an audio signal, by radio waves. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Amplitude modulation produces an output signal the bandwidth of which is twice the maximum frequency of the original baseband signal. Single-sideband modulation avoids this bandwidth increase, and the power wasted on a carrier, at the cost of increased device complexity and more difficult tuning at the receiver.

Both radios used vacuum tubes and employed Collins innovations including mechanical filters and permeability tuned oscillators. The latter alters the resonant frequency of a circuit by moving a sintered powder core in and out of the tuning coil using a lead screw. The KWS-1 final amplifier use a pair of 4X150 power tubes and operated at a power input of one kilowatt, the maximum allowed under Federal Communications Commission (FCC) regulations at the time. The transmitter appearance matched the receiver, but its high voltage power supply was packaged in a separate pedestal. [3] [4]

Vacuum tube Device that controls electric current between electrodes in an evacuated container

In electronics, a vacuum tube, an electron tube, or valve or, colloquially, a tube, is a device that controls electric current flow in a high vacuum between electrodes to which an electric potential difference has been applied.

Mechanical filter

A mechanical filter is a signal processing filter usually used in place of an electronic filter at radio frequencies. Its purpose is the same as that of a normal electronic filter: to pass a range of signal frequencies, but to block others. The filter acts on mechanical vibrations which are the analogue of the electrical signal. At the input and output of the filter, transducers convert the electrical signal into, and then back from, these mechanical vibrations.

Federal Communications Commission independent agency of the United States government

The Federal Communications Commission (FCC) is an independent agency of the United States government created by statute to regulate interstate communications by radio, television, wire, satellite, and cable. The FCC serves the public in the areas of broadband access, fair competition, radio frequency use, media responsibility, public safety, and homeland security.

In a 2006 review of the half-century-old 75A-4 [5] Stu Cohen wrote "Performance under all but extremely crowded band conditions is still excellent, and a 75A-4 will hold its own against almost any receiver. Under less crowded band conditions, the performance is superb."

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References

  1. ↑ Amateur Radio and the Rise of SSB, Gil McElroy, QST, January 2003 75A1
  2. ↑ Amateur_Radio.com
  3. ↑ KWS-1 The Care and Feeding
  4. ↑ Headquarter's staff, ed. (1958). The Radio Amateur's handbook (35th ed.). West Hartford, Connecticut: American Radio Relay League. pp. A27–A29.
  5. ↑ 75A4 Product review, QST Magazine, January 2006
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