Collins KWM-2 Vintage Ham Radio Transceiver

The Collins KWM-2 transceiver was a classic ham radio transceiver that other manufacturers sought to emulate - although not cheap it offered the ultimate performance for the time.

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The Collins Radio Company sought to design and manufacture the best they could in every aspect and all their equipment was of a very high quality.

The Collins KWM2 was the ultimate example of their engineering philosophy and RF circuit design. It was seen as the market leader of the time which can hold its own even today even though it is now a vintage radio.

The Collins KWM2 was an HF amateur bands only transceiver which was able to develop 100 watts PEP output on single sideband. Offering ease of operation along with a high performance specification it offered the ultimate for anyone who could afford it.

The KWM-2 had a distinctive style with its rounded edges and leather effect on the front panel. Even today, this radio would not look out of place in a modern ham radio shack.

Collins KWM2 specifications

The Collins KWM-2 provided a very good specification and operated well as a result. The RF circuit design utilised many aspects like balanced mixers and other high performance circuits to achieve this performance. In many respects it was well ahead of its time and now leads the field when compared to many other vintage radios of its time.

Brief Specification for the Collins KWM-2 Vintage Ham Radio Transciver
Parameter Specification
Basic description Double conversion superhet radio communications receiver with crystal controlled first local oscillator covering the amateur radio / ham radio bands up to 30 MHz.
Frequency coverage

Crystals were supplied with the KWM2 for the following bands. *
    80 metre band: 3.4 - 3.6, 3.6 - 3.8, and 3.8 - 4.0 Mc/s
    40 metre band: 7.0 - 7.2, 7.2 - 7.4 Mc/s
    20 metre band: 14.0 - 14.2, 14.2 - 14.4 Mc/s
    WWV: 14.8 - 15.0 Mc/s
    15 metre band: 21.0 - 21.2, 21.2 - 21.4, 21.4 - 21.6 Mc/s
    10 metre band: 28.5 - 28.7 Mc/s **

Modulation modes Single sideband - either sideband is selectable and CW
Signal power

SIngle sideband: 175 watts PEP input to plate and 100 PEP output
CW / Morse: 160 watts input 100 watts output, max 50% duty cycle

Transmitter harmonic & spurious outputs Carrier -50dB; unwanted sideband -50dB; second harmonic -40dB; oscillator feedthrough & unwanted mixer products -50dB; Third order distortion -30dB.
Receiver sensitivity 0.5µV for 10 dB signal to noise ratio
Receiver selectivity -6dB at 2.1 kc/s, -60dB at 4.2 kc/s bandwidth
Dimensions Width = 14¾" Height = 7¾" Depth = 14"
Weight 18 lbs, 3oz.

    * Although the KWM2 was the basic transceiver used, the KWM2A was a later development used by the US MARS or Military Affiliate Radio Service and other military organisations. It had an additional crystal board which enabled the Collins KWM2A to use an additional 14 crystals to cover frequencies outside the amateur radio bands. A front panel indicator was provided to show which band was in use.

    ** Only one crystal was provided for the 10 metre band as the whole band extends from 28.0 to 29.7 Mc/s and this allowed the owner to select the required crystals for the frequency range they required.

Collins KWM-2 basics

The Collins KWM-2 was introduced in 1959 as a successor to the KWM-1. The radio was most successful ever produced by Collins and was produced for over 25 years, being used by the amateur radio fraternity around the globe. It also appears that well over 25 000 of these sets were manufactured during its long production life. It certainly had many industry leading aspects to its RF circuit design.

A version of the transceiver known as the KWM-2A was produced for MARS - military affiliate radio system use as well as for other military applications. This radio provided the same amateur radio band coverage as the KWM-2, but also gave access to other frequencies as well. It was widely used by MARS stations in Vietnam and other locations to give phone patch connections for the US troops back to home.

In terms of its performance, the KWM-2 provided remarkable stability for its day. It had a dial that was able to provide the frequency (accurately) down to 1kc/s and the drift was also minimal at better than 100 c/s per hour. These were remarkable figures for the day and gave the KWM-2 a good lead over the opposition and set the standard for others to follow.

The KWM-2 used an external power supply. Two were available from Collins. The PM-2 was the lower cost version and had only a limited duty cycle which limited the operation of the radio, but was suitable for much intermittent operation. For more intense use and greater flexibility the 516F was recommended as it enabled the fully operational specification to be realised.

Collins KWM-2 valves / tubes

The KWM-2 circuit design used a total of 18 vacuum tubes or valves. Most of them were small B7G or B9A types but the two output tubes were much larger in view of the power handling capability required.

The line-up within the RF circuit design incorporated the following devices: 6AZ8, 6U8A, 6AZ8, 6AZ8, 12AT7, 12AT7, 6DC6, 7543, 6CL6, 6146A, 6146A, 6U8A, 6U8A, 6U8A, 6BN8, 6BN8, 6EB8, 6BN8.

Vacuum Tube / Valve Line-up for the Collins KWM-2 Circuit
Valve Number Type Use within the circuit
V1 6AZ8 A - First microphone amplifier
B - First receiver IF amplifier
V2 6U8A A - VFO cathode follower
B - Tone oscillator
V3 6AZ8 A - Microphone amplifier cathode follower
B - Second receiver IF amplifier
V4 6AZ8 A - Transmitter IF amplifier
B - VOX relay actuator
V5 12AT7 First transmitter mixer
V6 12AT7 Second transmitter mixer
V7 6DC6 Receiver - transmitter RF amplifier
V8 6CL6 Transmitter driver
V9 6146A Transmitter power amplifier - part of pair of output devices
V10 6146A Transmitter power amplifier - part of pair of output devices
V11 6U8A A - Beat Frequency Oscillator
B - second microphone amplifier
V12 6U8A A - Crystal calibrator
B- Crystal oscillator cathode follower
V13 6U8A A - High frequency crystal oscillator
B - First receiver mixer
V14 6BN8 A - VOX rectifier (one diode) & antiVOX rectifier (other diode)
B - VOX amplifier
V15 6BN8 A - AVC rectifier both diodes)
B - Product detector
V16 6EB8 A - First AF amplifier
B - Receiver AF output amplifier
V17 6BN8 A - ALC rectifier (both diodes)
B - Second receiver mixer
V301 7543 Variable frequency oscillator

Note "A" and "B" in the "Use within circuit" column refer to the sections of the tubes / valves where a device has more than one section to it.

In addition to the tubes / valves used within the KWM-2, a number of semiconductor diodes were also used and these undertook a variety of functions within the overall KWM-2 circuit.

In 1959 when the KWM-2 was launched, semiconductor technology was reaching the state where some devices could be used in high performance RF circuit designs.

Semiconductor Diode Line-up for the Collins KWM-2 Circuit
Diode Number Type Use within the circuit
CR1 - CR4 FA4000 Balanced modulator matched quad
CR5 HC7001 Receiver RF trimming
CR6 1N34A Calibrator harmonic generator
CR7 1N1490 Screen voltage gate
CR8 1N458 ALC static bias control
CR9 1N458 Receiver mixer isolator
CR10 1N1490 Cathode follower isolator
CR11 1N458 RF amplifier AGC time constant switch
CR301 1N34A Diode switch for C308

KWM-2 basic circuit description

The KWM-2 is an SSB and CW (no AM or FM) transceiver that operates between 3.4 and 30Mc/s. The receiver circuit uses a double conversion topology with a crystal controlled high frequency conversion (first conversion for the receiver) and a VFO controlled LF conversion.

The HF IF covers 200 kc/s between 2.955 and 3.155 Mc/s giving a flat response over 200 kc/s.

The low frequency IF is at the standard frequency of 455 kc/s.

In many respects, the the KWM-2 was a development that combined the Collins 75S-1 vintage radio receiver with the companion 32S-1 transmitter. However it used a technique called sidetone generation for CW which many thought was something of a compromise. Some modifications to provide carrier generated CW have appeared in the publications as the sidetone generation is not considered to be optimum for a variety of reasons.

In the design many circuits are common to the receiver and transmitter. The transmitter and receiver use common oscillators as well as a common mechanical filter and a common RF amplifier (but not the power amplifier). This reduces the number of circuits required and enables the power consumption as well as the size to be reduced.

As the KWM-2 was designed for mobile use as well as fixed station operation, size and power consumption were important aspects of the design.

The Collins KWM-2 rightly had an enviable reputation for performance and quality. Collins Radio aimed high in terms of overall performance and quality. With these radios still sought after today, it is clear that Collins succeeded with their KWM-2 making it a true classic vintage radio from the late 1950s which is still able to perform well today.

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