For the past couple of months, I was seeking a donor HW Monobander. But in truth, I actually had one in a storage area. We all know the huge issue of finding something in storage. Well, after several months of plaintive pleas for a donor radio, I was left empty handed. Thus, a sojourn to the storage area to retrieve the HW-32A. Yes, I had to go through all of the boxes, and it was the very last one.
Physically it is OK, but it has a significant circuit issue that after chasing it for some time I gave up. Thusly banishment to the storage area. So now I have to fix it. Yesterday I wrote the code for the ST7735 display and that is done. (More on this.)
The plan is to get the HW-32A working as designed and then the treatment with the JF3HZB dial.
I have done a fit check of several sizes of displays, but that semicircular hole is an odd duck. The panel space is 12X6 inches and I have a chunk of aluminum that exact size.
A potential possibility is to create a whole new front panel and cut a rectangular hole in the new panel for a Color TFT display. This approach would enable the use of a large ILI9341 display. The original panel would now be a template for cutting most of the holes in the new panel. A Juliano Blue or Canary Yellow color front panel would assure a notice.
But wait! This is a complex project because of what Heathkit did! That blog readers is the challenge. At times I just do things because I can but often because it is a real technical challenge. The Circular Analog Dial with the HW-32A is a Technical Challenge. Part of that challenge was highlighted in the past postings dealing with the 40M Channelized radio that was fitted with the same Heathkit crystal filter frequency.
Today, especially with the advent of Digital LO's and BFO's the single conversion topology is the circuit of choice. The real ham technical experts (the non faux wannabe's) will give full throated testimony to the soundness of the single conversion.
But the HW-32A is a Single Conversion Design and that is the challenge in the required engineering evaluation to make that work. Let's take a shallow dive into the issue. The Heathkit 4 Pole Filter is at 3.395MHz and the heterodyne frequency is at 18.275 MHz (simple Crystal Oscillator) and is added/subtracted to the VFO frequency to form the LO.
Shazam, Heathkit used a VFO operating in the range of the broadcast band. In fact, I think that is one of the operational checks to see if the VFO is working -- listen for it on your AM radio. This low VFO range when mixed with the fixed heterodyne signal made for a far more stable radio than a VFO operating at 10+ MHz.
Now I earlier said I got the JF3HZB code working for the HW-32A. Well, that was only to see how it would look on various displays and how the front panel will look with the various sizes. It is not the final design!
So here is an array of technical challenges. Throw it all away, keep some or only use the JF3HZB as the VFO. Each of these involves a significant modification to the radio and the sketch. The change the VFO only option involves a bit of code trickery because of the heterodyne VFO conversion.
Let me explain the last option. You want the display to show as in the second photo. But the original JF3HZB code is based on single conversion with a subtraction of the 3.395MHz IF. This has to be accounted for in the code and since we have a subtraction it will be a sideband inversion and the frequency actually subtracted is not 3.395 but 3.396500 MHz, the USB BFO so that the dial reading is accurate.
Heathkit did make it somewhat easy as the VFO and Heterodyne Oscillator (V13 and V14) have their filaments series connected. Simply pulling those tubes out of their sockets is all that is needed to null those functions. A new LO from CLK0 can be introduced into L5 and that solves the problem of a single conversion.
Still another waypoint decision, the BFO. The HW-32A has selectable sidebands and so do we keep that function or disconnect the crystals and simply feed CLK2 into the grid of the Carrier Oscillator. The former USB/LSB select switch could now be an input to the ESP32 to provide the proper Carrier Frequency. Is there a possibility of generating a USB Carrier and the other a CW carrier on transmit and use the HW-32A on CW? More complexities
So, the real thrust is to get the HW-32A working as stock. My past foray on getting it proper was L2 and L3 as the signals (both on transmit and receive) were in serious need of a shot of Viagra.
L3, which is in the plate circuit of the 12BY7 Driver Tube has a link coupled winding from the antenna relay and thus is also in the receive path. A limp signal on Rx and Tx would sure point to that area of the circuitry. Faint signals and but a few watts on transmit are the symptoms.
This could be a serious overall technical challenge and another adventure at the N6QW Laboratories.
Them that know can make things go!
73's
Pete N6QW