Lowe Electronics - The HF150

It was a simple joy to work on projects that became the classic Lowe Radio Range.

The HF-150 is a double conversion superhet with two IF filters, nominally 6.5 and 2.6 kHz. They are selected by mode making operation easy for the novice listener.

The AMS detector in the HF-150 is much better than in the older radio. For one thing, it allows selection of upper or lower sideband. It also hangs on to the carrier for dear life! The radio will lock on to the weakest carriers too. It's also standard equipment.

The HF-150 measures just 7.25 x 3.125 x 6.25 inches. Its case is made of heavy gauge extrude aluminium, so the receiver will take a lot of stick. The HF-150 is powered by 8 penlight batteries and a new set of alkalines only lasts about 5 or 6 hours as the computing is old tech. An AC adaptor is supplied with the radio.

The HF-150's front panel is very clear. A frequency display, tuning knob, three push buttons, a volume control and a headphone jack. One important control has been banished to the back panel; the 20dB attenuator. With no bandpass filters like its older sibling, it can be overloaded by strong signals. But who cares...

The HF-150's lack of RF input filters can cause problems when the set is operated near a powerful radio transmitter. Use of the attenuator helps considerably. With a loop antenna, active or passive, they are among the most sensitive receivers available.

Press the MODE button and the display changes to show the mode in use. You can then press the right or left buttons to move from mode to mode. The AM (A) synchronous double sideband (ASd) and Hi-Fi (ASF) modes all use the wider filter; the remaining modes utilise the narrower filter The ASd mode is similar to that found on the HF-225 and is best for normal listening. The ASL and ASU modes produce very pleasant audio even though they utilise the narrow filter. When a signal is in the clear, switching to the Hi-Fi ASF mode yields wonderful results. This mode uses the same, wide IF filter as ASd, but changes the BFO injection frequency to recover more high frequency information. Lowe rates the audio frequency response in ASF mode at 20 Hz to 5.5 kHz, about as good as AM radio gets.

The HF-150 has only one memory mode, called preview and you must press the RECALL button to tune the set to the stored frequency. However the keypad is must more useful: punching in any number between 1 and 60 and pressing the # sign will tune the radio to the frequency and mode stored in that memory. The HF-150 requires you to press only one button to store the radio's setting in a memory.

Signals from the antenna are passed through a switchable 20 dB attenuator and a 30 MHz low pass filter to the RF port of a transistor tree mixer, where the RF signal is mixed with a local oscillator to upconvert it to the first IF or 45 MHz. The first IF is passed through a PIN attenuator (for AGC) then through a 15 kHz crystal filter and on to the second mixer's input port. Here the 45 MHz signal is mixed with a heterodyne oscillator that tunes between 44.544 and 44.545 MHz in 128 steps, giving an effective tuning rate of 7.8 Hz per step. The resulting 455 kHz IF passed directly to the selectable IF filters. These filters, nominally 6.8 and 2.5 kHz are selected by diode switches controlled by the radio's microprocessor. The radio's first IF amplifier follows these filters.

The HF-150 has two IF amplifiers each feeding a separate 6.8 kHz IF filter, so there are three IF filters in the circuit at all times. The output of the IF chain is sent to an envelope detector for normal AM reception and to a product detector for SSB an d synchronous AM detection. A fixed frequency BFO supplies carrier for detection of SSB or CW signals while the BFO's frequency is varied by a control loop that's phase locked to the received carrier, for synchronous AM reception. Lowe performs a neat trick here, too: by increasing the BFO's offset frequency in the ASF Hi-Fi mode, the same IF filters can be audibly widened thus producing more treble in the output.