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| Heathkit 2036 VHF Transceiver after the restoration |
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How I Found the Heathkit HW-2036A at a Montreal Flea Market
One of the active clubs in Montreal, WIARC, organizes a small flea market every fall where usually 15-20 people set up tables. The previous year I had arrived quite late and walked in almost at closing time. I spotted this unit on one of the tables there (in fact, two of them were stacked on top of each other). Partly because the seller was eager to pack up his boxes and leave, I bought it for what I'd call pocket change and tossed it in my bag. Let me be frank, I had bought it only because I was curious about its construction, and I might not have bought it had the selling amateur not offered such a low price. Good thing I did! As you'll read, it turned into a project that was both very enjoyable and very educational, spanning 4 months.
Heathkit's 2-Meter VHF Radio Lineup: From HW-202 to VF-7401
Now let's get to know the unit a little (I don't feel the need to talk about the Heathkit company again, I had written about it at length before, you can read it in that post). The HW-2036 is one of the mobile VHF radios that Heathkit introduced in the late 1970s. Heath had released a series of radios for the 2 Meter band starting from the early 70s. The first of these was the crystal-controlled, 6-channel HW-202 (1973). It was followed by the synthesized HW-2026 (1975), but that turned out to be such a problematic design — especially in terms of spurious emissions — that for the first time in the company's history, a product was recalled from the market. The HW-2036, which came after it, was in a way the result of lessons learned from the 2026 (1976). Finally, the VF-7401 came out (1980). The 7401 was a more advanced unit featuring an LED display and scanning capability. Let me also note that all of these were sold as kits. Apart from using the same enclosure, there are also common points in their circuit designs, which you can see when you look at the boards.
Don't assume they were cheap just because they were kits, either. In 1978, an HW-2036A was 269 US Dollars; the equivalent of that amount today is $1,911!
The HW-2036 is the most common among these kit radios. There is also an HW-2036A version. The difference is that the first one covers 2 MHz of bandwidth on the 2 Meter band, while the second covers 4 MHz. However, so that those who had jumped in early and bought the HW-2036 wouldn't feel left out, Heathkit also released a modification kit — you could replace certain parts and convert your unit to the A version. The one I have is one of those units with this modification applied. According to the label on the bottom, the unit was completed on April 17, 1977. These labels came as part of the kits and carry the statement "I hereby declare that this unit I have completed complies with FCC standards." The amateur who finished building it would sign the label and stick it to the bottom of the enclosure. Therefore, each unit has its own serial number.
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| Heathkit HW-202 - Crystal Controlled (1973) |
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| Heathkit HW-202 from Heathkit 1978 Catalog |
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| Heathkit 2026 - Synthesized (1975) |
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| The recall letter from Heathkit's president to radio amateurs. Heathkit entirely refunds you and pays your postage fee if you prefer to return your HW-2026. Additionally, you get a gift certificate of 50 USD if you already finished the assembly, if not, you get a 25 USD certificate. |
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| Heathkit HW-2036 (1975) |
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| Heathkit HW-2036 in 1978 Heathkit Catalog |
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| Heathkit VF-7401 (1980) with digital display |
HW-2036A Technical Specifications
Now let's take a look at the technical specifications of the HW-2036A:
Operating range: 144 - 148 MHz
Sensitivity: 15 dB quieting with -113 dBm (0.5 uV) signal
AF output power: 1.5 Watts
RF output power: 10 Watts
Modulation:
FM, adjustable 0 - 7.5 kHz
Duty Cycle: 100% (at infinite VSWR)
Tones: 3 adjustable tones between 70 - 200 kHz
Transmit offset: Crystal controlled, 3 options: +600 kHz, -600 kHz, extra (left empty for adding a crystal with the desired frequency offset later)
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| Heathkit HW-2036 Block Diagram |
How the HW-2036A PLL and VCO Circuit Works
The heart of this transceiver is a voltage controlled oscillator (VCO). The VCO is also part of the phase locked loop (PLL) that determines the frequency the unit will operate on and keeps it on that frequency. You set the desired operating frequency using three mechanical BCD (binary to decimal) switches on the front panel. There is also a switch that sets the last digit to either 0 or 5 (Hz). A phase comparator divides the signal coming from the VCO by this number and compares the result with the signal coming from a reference oscillator, and if there is a phase difference, it corrects it by changing the voltage on the varicap diode in the VCO.
The signal coming from the VCO is one sixth of the desired actual operating frequency, and the signal is multiplied by six in both the receiver and the transmitter. In the transmitter, the power is boosted to 10 W at the final output stage.
The receiver mixes the signal arriving at the antenna with the sixth harmonic of the signal from the VCO, passes the resulting 10.7 megahertz intermediate frequency signal through an eight-pole crystal filter, amplifies it and then converts it to a 455 kHz intermediate frequency. This signal is separated by the detector and sent to the audio frequency amplifier to be amplified.
As we can see, it may seem very simple compared to today's microprocessor-controlled radios, but it is by no means a "simple" unit (I'm saying this excluding software defined radio technology). What we have here is a PLL-controlled radio that can still do its job 40 years after its design...
In the next part, we will look at the problems with the HW-2036 that came into my hands and how I fixed them.
Also: I have explained the details of this restoration in 4 parts on my Youtube channel as well, you can watch it here.
FAQ
What is the Heathkit HW-2036A?
The HW-2036A is a PLL-controlled, 10-watt, 2-meter FM transceiver introduced by Heathkit in 1976. It was sold as a kit and covers the 144–148 MHz range.
What is the difference between the HW-2036 and HW-2036A?
The HW-2036 covers 2 MHz of bandwidth on the 2-meter band, while the HW-2036A covers 4 MHz. Heathkit also offered a modification kit to convert the original HW-2036 to the A version.
How much did the HW-2036A cost when it was new?
In 1978, the HW-2036A kit was priced at $269 USD, which is equivalent to approximately $1,911 today.
How does the HW-2036A frequency control work?
The transceiver uses a phase locked loop (PLL) with a voltage controlled oscillator (VCO). The operating frequency is set via three BCD switches on the front panel. The VCO output is one sixth of the actual operating frequency and is multiplied by six in both the receiver and transmitter stages.
What other 2-meter radios did Heathkit make?
Heathkit released four 2-meter radios: the crystal-controlled HW-202 (1973), the synthesized HW-2026 (1975), the HW-2036/2036A (1976), and the VF-7401 (1980) which featured an LED display and scanning capability.
Why was the Heathkit HW-2026 recalled?
The HW-2026 had serious problems with spurious emissions, making it the first product in Heathkit's history to be recalled from the market.
Links:
My videos on the restoration of HW-2036, part 1: Click here to watch
My videos on the restoration of HW-2036, part 2: Click here to watch
My videos on the restoration of HW-2036, part 3: Click here to watch
Robert Sumption's video on the general modifications in HW-2036: Click here to watch
Heathkit 2036 Manual courtesy of W5RKL: Click here to download
Heathkit 2036 Manual (includes schematics) courtesy of Vintage Radio Info : Click here to download
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