Hallicrafters FPM-300: The Last SSB-CW Transceiver

Introduction

In 1971, Hallicrafters introduced the FPM-300 single-sideband (SSB)-CW transceiver, designed for the 80/75 to 10-meter amateur radio bands. A minor update was made in 1972, and it was sold until the company closed in 1974. This radio distinguished itself from earlier Hallicrafters products by including a built-in power supply (AC and DC), a speaker, voice-operated transmit (VOX), and a crystal calibrator.

Design and Features

The FPM-300 featured a solid-state design, with the exception of two vacuum tubes: the driver stage and the final amplifier (a 12BY7 and a 6KD6). A key design element was its ability to tune across all bands in the same direction, unlike many contemporary transceivers. While the created and received sideband changed depending on the band, the transceiver's band switch ensured the selected sideband remained consistent from the operator's perspective. The radio was factory-equipped for the 28.50 to 29.00 MHz segment of the 10-meter band, which was the primary area for phone operation at the time. Modern amateur radio bands have shifted, with phone operation often starting at 28.30 MHz, though some radios like Heathkit and Swan offered full 10-meter coverage.

The FPM-300's top cover was hinged at the rear and secured with latches on each side, providing access to internal controls, including those for VOX operation. The radio generated a CW signal using a sine wave tone fed into the SSB input, with the VOX activating transmit mode for CW. Optimizing VOX settings for SSB and CW required separate adjustments, which could be cumbersome as the controls were not independently adjustable. The CW tone frequency was approximately 1750 Hz, which was higher than what many operators preferred or were accustomed to, potentially making it challenging to maintain the FPM-300 on the exact frequency during CW transmissions.

Figure 1: A textual description of the Hallicrafters FPM-300 Transceiver, showing its front panel and overall form factor.

Figure 2: A textual description of the FPM-300 front panel. Key controls visible include REC GAIN, PA LOAD, PA TUNE, BAND, PRESELECTOR, FUNCTION, MODE, and MIC/CW LEVEL. It also shows indicators and tuning dials.

Options and Accessories

Unlike many Hallicrafters products, the FPM-300 had limited optional accessories. These included crystals for full 10-meter coverage, an optional cooling fan for the vacuum tubes, a power cord, and a mounting bracket for mobile installations.

Power Supply

The FPM-300 featured an AC/DC power supply. The AC input used a single power transformer with two primary windings, configurable for 120V AC (parallel) or 240V AC (series) input. The DC power supply operated with a 13.8V DC negative ground source. A small feedback transformer was used to sustain oscillation for the inverter transistors when operating on DC power. This DC operation was compatible with most 12V automobiles, noting that older models like the 1955 Packard used positive ground systems before transitioning to universal negative ground configurations.

New Components and Technology

The FPM-300 incorporated several modern components for its time. The product detector utilized the Motorola MC1496G double-balanced mixer. A packaged double-balanced four-diode mixer was employed to combine the VFO with the crystal oscillator for band definition. Analog integrated circuits (ICs) were used in the IF amplifier stages. A divide-by-four IC was used to convert the 100 kHz calibrator signal to 25 kHz. The design also featured junction field-effect transistors (FETs) and dual-gate metal-oxide silicon FETs (MOSFETs) in various roles, including oscillators, amplifiers, and mixers.

The transceiver included a meter that functioned as a signal strength indicator during receive and as a cathode current meter for the final amplifier during transmit. The frequency dial markings were at 10 kHz intervals, though the knob's divisions offered limited calibration assistance. Tuning was generally smooth, with stability varying among units; the reviewed unit exhibited minimal drift.

Figure 3: A textual description of the FPM-300 rear panel. Connections include ANTENNA, RELAY, KEY, and GROUND. Power input options for 117/234V AC (50/60 cycles) and BLOWER, FUSE, and a 25 KHz FREQ. ADJUSTMENT control are also visible.

Errors in the Manual

Some versions of the Hallicrafters operating manual contained inaccuracies. For example, the receiver product detector was misidentified as a Motorola MC1498G instead of the correct MC1496G. The final amplifier vacuum tube was listed as a type 8KD8, when it is actually a 6KD6. Similarly, an optional cooling fan kit was incorrectly identified as HA-80 instead of HA-60. These errors were not present in all manual versions, notably the online version.

Overall Impression

For amateur radio operators who acquire an FPM-300 with good frequency stability, the primary operational considerations are the 10 kHz frequency readout divisions and the method for setting VOX controls for SSB and CW. The 1750 Hz CW tone may be a drawback for some users. Despite these points, the FPM-300 is described as a pleasant rig to use, benefiting from its integrated crystal calibrator, VOX, and easily accessible top cover.

Related Publications

The article also notes two books:

• George J. Whalen, NY9A, published "The Story of Radio: To 5G Wireless," detailing radio technology history and evolution.
• Peg Nichols, KDØVQO, published "Sidewalk Sale Across America," a snapshot of the COVID-19 pandemic's impact on amateur radio. This book is available on Amazon.com.