Note
This was Heath’s first HT and it was a real handful (see dimensions below). The HW-2021 is a 1 watt, 5 channel, crystal-controlled unit.
Assembly of the HW-2021 was tricky, demanding a small soldering iron and a steady hand as parts on the board were tightly packed. The unit approaches the limit of what is possible to assemble by hand.
The HW-2021 suffered from a variety of problems resulting not only from difficulty in assembly, but also from a number of design faults. By October 1976 Heath had issued more than 20 service bulletins for the unit. A modification kit was offered to owners, and the fixes were eventually incorporated into an improved kit, and by all rights should have changed the model number to HW-2021A, but Heath didn’t do that. Units with an assembly manual numbered I-525-1742-02 contain all of the improvements. If an assembly manual is not present, one way to determine if the unit in question is an improved type is to determined the value of resistor.
If R63 is 6800Ω (blue-gray-red), the unit is improved. If R63 has a small choke in series with it, the unit was upgraded by a Heath service center. If the choke is not present, the unit is a factory original improved version. More than a dozen component changes and other modifications were made in the improved version.
The same crystal is used for both transmit and receive, and an offset switch lets you use any of the frequencies as a simplex, or shifts the transmit frequency 600 kHz below the receive frequency. It is important to note that the offset is accomplished by a crystal and can be plus or minus 600 kHz—but not both, since there is room for only one offset crystal. The HW-2021 came standard with the crystal for a transmit for minus 600 kHz operation. Other offsets are possible with the right crystal installed.
There is no provision for CTCSS tones.
A four-pin battery charging connector is located on the bottom of the unit. Only the outer two pins are used. An AC or DC source can be used for charging, and polarity is not critical because of the HT’s internal bridge rectifier. Heath provided a charger in the form of a power cube. The cube contained only a transformer. All of the rectification is done onboard the HT.
Note: The charging scheme is not sophisticated, and works by limiting the charging current to about 60 mA. Current limiting is accomplished by the transformer in the cube, not by any external circuitry. The charger provided by Heath can be connected for long periods without danger of overcharging.
Note: If you use a 12 VDC source to charge the HT, current should be limited to 60 mA. An AC source should provide about 9 volts, also limited to 60 mA. Note that if an AC source is used, no filtering of the rectified DC is provided for inside the HT. Transmitting while using an AC power source will cause a hum on the transmitted signal.
The HW-2021 was “not recommended for beginners because of its compactness,” and was replaced by the VF-2031 in 1978.
CRYSTAL FREQUENCY CALCULATIONS
Channel crystals:
When installing crystals, always calculate for the receive frequency.
crystal frequency = (receive frequency in MHz – 10.7) / 9
Transmit offset crystal:
For transmit below receive:
crystal frequency = 10.7 MHz – offset frequency in kHz
For transmit above receive:
crystal frequency = 10.7 MHz + offset frequency in kHz
Crystal Specifications
tolerance: 0.0025%
load capacity: 32 pF
effective resistance: 40Ω
holder: HC-25U
References:
Review. QST. Jan 1977, p. 36.
Review. CQ. Jun 1976, p. 22.
Review. 73 Amateur Radio. Aug 1977, p. 160.
Add switch selectable offsets. 73 Amateur Radio. Jan 1978, p. 180.
Touch Tone encoder instability. 73 Amateur Radio. Aug 1978, p. 60.
Several improvements. 73 Amateur Radio. Oct 1978, p. 54.
RECEIVER
Sensitivity: 20 db quieting @ 0.75 µV
Squelch threshold: 0.3 µV or less
Audio output: 0.5 watts at less than 10% THD
Stability: 0.005% or better
Image rejection: –45 db or greater
IF frequency: 10.7 MHz
Modulation acceptance: ±7 kHz maximum
TRANSMITTER
Power output: 1 watt minimum
Stability: 0.005% or better
Oscillator frequency: approximately 15 MHz
Multiplier: x 9
Modulation: FM
GENERAL
Speaker impedance: 8Ω
Operation frequency range: 143.9 to 148.4 MHz (any one MHz segment within the range)
Operating temperature range: +10F to +120F
Power requirements: 12.5 VDC nominal
Solid State:
diodes: (6) 1N2071, (8) 1N458, (5) 1N4149, (1) 1N191, (1) MV1404, (1) VRS-5A
transistors: (4) 40673, (1) MPS6520, (3) 2N5770, (1) MPS6521, (7) 2N3393, (1) X29A829, (1) 2N5308, (5) 2N2369, (1) 2N5913, (1) MPF105, (1) UC734
integrated circuits: (1) CA-3089, (91) MC14554, (1) 741
Photos, general information and specifications from "Heathkit: A Guide to the Amateur Radio Products," by Chuck Penson, WA7ZZE. Used with permission.
