Equipment Reviews, September 1999
The NASA HF-4 Communications Receiver
I don’t know the background to the name changes, but the NASA HF-4 is clearly a refined version of the Target HF-3 receiver that I reviewed in the April, 1997 Journal. The HF-4 is now distributed by Deltron Communications International.
For those who who have access to the HF-3 review, I’ll list the changes made in the HF-4. The major changes are: the inclusion of a 2.6 kHz filter in addition to the original 6 kHz filter, a lighted display panel, expansion of the available memory channels from one to ten, addition of a RS232 jack to permit reception of weather fax transmissions (PC software and cable included) and substitution of a SO-239 antenna connector for the RCA jack used on the HF-3. In addition, there is a back-panel slide switch to apply 12 volt DC power to the antenna connector to be used with the NASA AA-30 active antenna or any other active antenna that can be remotely powered.
Small And Compact
The HF-4 uses the same compact case as the HF-3, measuring 21/2 x 71/4 x 7 inches (HxWxD), but the case color is now black instead of gray. There is a tilt-down bail to elevate the front of the radio for easier viewing. The control layout is the same: three knobs for Power/Volume, Clarify and Tuning and four pushbuttons for mode and memory functions. The well-illuminated LCD display shows the tuned frequency with a resolution of one kilohertz and has a ten segment bargraph S-meter which doubles as the memory channel indicator. There is a top-mounted four inch speaker. On the back panel are the antenna jack with a solder lug for a ground connection, 1/8 inch jacks for external speaker/headphone and data out and switches for attenuator, filter selection and active antenna power.
Note that the active antenna power switch must be in the “Off” position if the radio is used with an antenna that has a DC connection to ground, such as an antenna with a balun, otherwise the power supply will be damaged. Also don’t turn on the active antenna power if an external device such as a preselector is used in the antenna line. Inserting a plug into the speaker jack defeats the internal speaker and note that the data out jack is just for computer decoding of signals, not computer control of the radio.
No power supply comes with the radio but a fused power lead is included. Any source of 12 volt DC power can be used, as long as it is capable of supplying at least 300 milliamps of current. Also included is the computer cable, a length of wire with attached banana plug for use as an antenna and a spade lug to connect a ground. The U.S. selling price has not yet been set.
The HF-4 covers a frequency range of 30 kHz to 30 MHz without gaps. The receiver design is a synthesized double superheterodyne with intermediate frequencies of 45 MHz and 455 kHz. The smallest step of the main tuning is in one kilohertz steps, but the Clarify control provides fine tuning of +/- 800 hertz. The Clarify control is active in both AM and SSB modes and does not affect the digital frequency display. The tuning knob tunes in varying rates of 10 kHz, 100 kHz, 1 MHz or 10 MHz, depending on how quickly the knob is turned. Sensitivity is rated at one microvolt (test parameters not given) and selectivity is spec’ed at 6 and 2.6 kHz with no mention of skirt measurements. Audio output is rated at 2 watts.
When the HF-4 is powered up, the radio tunes to the frequency stored in memory channel one. The desired frequency can then be selected by turning the tuning knob. Tuning is quite smooth due to the heavy metal flywheel on the tuning encoder. The HF-4 variable tuning rate is not as “twitchy” as that on the HF-3, i.e. there were no sudden frequency shifts as the tuning knob was rotated. On the other hand, I had trouble getting the tuning to shift into “hyperdrive”the 10 MHz per revolution speed for bandswitching. A “fast” button to lock in the faster tuning rate (as on the TenTec 1254) is much more convenient.
Memory channels are selected by pressing the “RCL” (Recall) button. The radio defaults to memory channel twothe tuning knob can then be used to select the other memory channels. While in memory mode, the frequency stored in the memory channels cannot be tuned. Pressing “RCL” again puts the selected memory into the VFO. By pressing the “MOD” key when the radio is in the memory mode the radio returns to the last tuned frequency in the VFO. Pressing “RST” (restore) in either the VFO or memory mode, resets the radio to the frequency stored in memory channel one.
AM, LSB or USB modes are selected by pressing the “MOD” key when in VFO mode. Fine tuning of SSB signals is accomplished by using the Clarify control, which is also active in AM mode. Using the Clarify control in AM mode is useful with the narrow filter to shift the tonal response for better fidelity. Switching from USB to LSB mode for ECSS reception of AM signals requires retuningup two kilohertz from the carrier frequency for USB and down two for LSB. ECSS tuning works better on the HF-4 than on the HF-3, but still requires a delicate touch on the clarifier control. In SSB mode, the narrow filter is switched in, with no capability to select the wider filter.
The HF-4 is a significant improvement over its predecessor. The addition of a narrower bandwidth filter and the 10 memories make it much more versatile. It remains a basic, no frills receiver, but it has excellent sensitivity and very good audio quality. My major complaint is the variable rate tuningI had trouble getting it to “scoot” across the bands and, occasionally, the faster tuning rate would engage just as I was approaching the desired frequency and overshoot it by a wide margin. In addition, the unit’s light weight would permit it to move across the desk while trying to spin the tuning knob to engage the faster tuning rate. Tuning at the slower speeds was smooth and stable, however.
This is not a feature-laden DX machine, but it is a credible performer, suitable for a first receiver or as a second receiver for spotting or program listening. Its small size makes it ideal for field use, although there is no built-in battery capability. Its sensitivity makes it suitable for use with small antennas and I noticed no overloading problems with full-size antennas. Thanks to Universal Radio for providing the review unit.