The Lowe HF150
The lower priced HF-150 is a double conversion set and has two IF filters, nominally 6.5 and 2.6 KHz. Unlike the filters in its big brother, the ones in the HF-150 are selected by mode, so you cannot "open up" the selectivity when in SSB. This is no t a big problem because the set's PLL s but the user can over-ride the selection and choose his own alternative, which the receiver remembers when mode changing.
The KPAD-1 simply plugs into a socket already provided on the rear of the HF- 150 and allows direct entry of any frequency in theynchronous detector will lock on the weakest signals and it allows selection of filter width. The HF-150 has no noise blanker. 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 external keypad cost extra, but it's worth it. The HF-150 is only about half the size of its big brother, measuring 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 ban ging around. The HF-150 is powered by 8 penlight batteries and a new set of alkalines only lasts about 5 or 6 hours, because of the heavy current drawn by the set. An AC adaptor is supplied with the radio.
The HF-150's front panel, like the radio itself, is very compact. There's the same frequncy display and tuninng knob as on the other receiver, but it has only three push buttons, a volume control and a headphone jack. The display isn't lighted and there's no meter or tone control. One important control has been banished to the back of the HF-150 : the 20 dB attenuator. Since the new set doesn't have RF bandpass filters like its older sibling, it can easily be overloaded by strong SW and MW signals.
The preselector is essential with the HF-150 at my location because it contains a high pass filter that suppresses the MW band. For MW operation on either radio an external loop antenna is ideal.
The HF-150's two IF filters don't allow the latitude of control enjoyed when using the older receiver, but they are quite good, nonetheless. I've had little trouble seperating 49 metre band signals with the new set, and the radio's AMS detector often makes listening somewhat easier. For really tough cases, you can switch to USB or LSB and tune the station in ECSS.
The HF-150 is far better portable receiver than its old brother. Besides being considerably smaller, the radio's built in whip amplifier is far less susceptible to intermodulation and overload than the earlier version, offered as an option for the HF-225 . About the only drawback I can find is that the radio is somewhat microphonic, so a thumb on the bottom of the cabinet can produce a "ping" in the audio. High audio levels can also cause feedback if you're using the internal speaker. The manual warms ab out this and suggests using an exteranl loudspeaker or headphones because of it. The microphonics are traceable to the receiver's mixer stages, which are operated near their optimum design points. Transistor ring mixers of the type used in the HF-150 are notorious for being sensitive to vibration, but the "ringing" isn't detrimental to the set's operation.
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, but the set really needs a MW input filter when used in an urban area, I think. Neither of the Lowe receivers works well on MW frequencies in an urban area unless you use a tuned loop antenna. With a loop, active or passive, they are among the most sensitive receivers available. On the HF-150 I miss the S-meter and the tone control.
On the HF-150, the modes and bandwidths are selected by pushbuttons in a (gasp!) carousel arrangement. 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. Unlike t he Drake R8, however, this carousel moves in both directions. The AM (A) synchronous double sideband (ASd) and "HiFi" (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. Their rejection of the unwanted sideband is quite adequate, although I haven't measured it. When a signal is in the clear, however, switching to the "HiFi" 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 a t 20 Hz to 5.5 KHz, about as good as AM radio gets.
Moving from band on the HF-150 is easier than on the older receiver, too. A press of the FAST button causes the radio to tune in 100 KHz steps, during which the two rightmost digits in the display are blanked. If you're tuned to Athens on 9395 KHz and decide to see how London's doing on 12095 KHz, press the FAST button and whip the dial around to 12.0 then press FAST again. Voila! 12.095 MHz. The rightmost digits are preserved when you QSY in this way. Both sets emply variable increment rate (VIR) tuning, so that rapid turning of the knob can cause you to overshoot your target frequency. Slow and steady tuning prevents this, of course. Rapid tuning of the HF-150 also causes the radio to switch from synchronous mode to straight, envelope detected AM. Af ter you settle on the new frequency for a few seconds, the synchronous detector kicks back in again. This can prove a little disconcerting at times, because the radio's likely to emit a loud heterodyne whistle until the new station is properly tuned. Even so, I like Lowe's method better than the one used in the Drake R8, where you must re-engage the synchronous detector after retuning.
The HF-150 has only one memory mode, called "preview" and it works like the "preview" mode on the HF-225 you must press the RECALL button to tune the set to the stored frequency. However the keypad is must more useful on the newer set: 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. Unlike its older brother, the HF-150 requires you to press only one button to store the radio's setting in a memory.
Unlike its big brother, the HF-150 has no RF bandpass filters to aid its front end selectivity. This causes problems when the radio is used near a powerful MW or SW transmitter. Since I live in such a location I've found it necessary to front end the rec eiver with a tunable preselector. An external MW filter such as the Palomar Amplifier or the NCP MW filter should work just as well. The receiver has more than enough sensitivity throughout its frequency range so that an amplifying preselector or preamp isn't necessary. I use a Palomar P-408 simply because I have one on hand. 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 oscill ator 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 tr ick here, too : by increasing the BFO's offset frequency in the ASF "HiFi" mode, the same IF filters can be audibly "widened" thus producing more treble in the output.
SIDEBAR- The Lowe Listeners' Guide
Packed along with each Lowe receiver is a little gem of a book called The Lowe Listeners' Guide, which serves as an introduction to DX-ing without attemping to provide one of those frequency lists that's invariably outdated. This little book covers an aw ful lot in its 60 odd pages, and does it with a dry, refreshing wit. I' ve been DXing for more than 40 years, yet I found things in the little Lowe book that I' d never tried.
It begins with some pointers on antennas, then moves on to a guide tour of the spectrum from ELF through 30 MHz. Here's a sample of what you'll find "off the beaten track" "If you really want to frighten yourself, a couple of transistors and a few large coils can be cobbled into an ELF receiver. Around 10 KHz or so the action of static discharges anywhere in the atmosphere, coupled with changes in the earth's magnetic field, create "Whistlers", not unlike the cry of a rough whale. Very eerie all this. All worthy of John Carpenter..."
While it's written from a European perspective, with a distinctly British accent, the information contained in Lowe's wonderful little Listeners' Guide is perfectly valid anywhere on earth. Like the receivers it accompanies, The Lowe Listeners' Guide is for shortwave connoisseurs. Priced at only 1.95 (about 3.50) it would make an ideal stocking stuffer for any short wave aficionado.