Heathkit HW-2036 VHF Transceiver Restoration - Part 2

In brief: This post is the second of a 3-part series about the restoration of a Heathkit HW-2036A, a PLL-controlled, 10-watt, 2-meter FM transceiver from 1976 that I picked up for almost nothing at a flea market in Montreal. In this part, I cover the problems I found after bringing the unit home—from a stuck screw to low output power, a faulty DTMF keypad in the Micoder microphone, and unconfigured CTCSS tones—and how I diagnosed and fixed each one on the transmitter side. The next part will cover the receiver repairs.

The bottom side of Heathkit HW-2036, while working on the receiver board.

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Initial Inspection and Findings

In my previous post I had covered the features of the HW-2036 in general terms. Therefore, I will talk directly about the unit I bought from the flea market. After bringing the radio home, I first gathered the relevant documentation on the Internet. Thankfully, accessing detailed information about the HW-2036 was extremely easy. In addition to Heathkit's carefully prepared assembly and alignment manual, schematic diagram, and service bulletins, there were web pages or videos from amateurs who had previously worked on this unit. I collected these and noted down the information I personally found important.

Then, at a suitable time, I examined the unit. First, I looked for signs that could indicate other problems, such as impact marks or corrosion. I then opened the bottom section of the case and inspected the circuit board and components. I wanted to do the same on the top side as well, but I couldn't because one of the screws at the back was spinning freely. I then applied power and observed the unit's operation. My initial findings were as follows:

1. Since the case could not be fully opened, it was not possible to inspect the receiver and synthesizer boards. The first problem to be solved was this screw.
2. The unit was transmitting and receiving in both simplex and duplex modes, and there were no issues with the frequencies.
3. The transmit output power was far below what it should have been.
4. When listening from another radio, my voice sounded muffled as if coming from the bottom of a well. In addition, a strange tone was heard, resembling the noise of a discharging capacitor (reminding me of simple siren circuits).
5. The receiver was somewhat deaf. The squelch was opening at around -95 dBm, and it was practically "not hearing" signals weaker than -105 dBm.
6. The S-meter was not working, and the illumination lamp had burned out.

Removing the Stuck Screw

Based on these findings, the first thing I tackled was the freely spinning rear screw. In order to remove it with a screw extractor bit, I first secured it with epoxy adhesive. Then I drilled a small cavity in the screw head with a drill, and finally removed it from its place with the screw extractor bit. This allowed me to access the circuit boards inside. Meanwhile, since I didn't want to replace just a single screw, I sourced screws of the appropriate diameter and length ("6#-32" in American measurements) and later replaced all the top case screws with new ones. When I removed the screw, I saw that the problem originated from the standoff inside—it had been spinning freely because it was not fully tightened from the other end. I applied a drop of super glue and retightened it.

Heathkit HW-2036A's back side and the screw I had to 
immobilize with epoxy glue before drilling.

Heathkit HW-2036A's back side - the bad screw is ready for extraction.

Transmitter Board Overview

Once the inside of the unit became fully visible, I examined the circuit boards and traced the circuit paths according to the schematic diagram, noting down the reference voltages marked on the schematic and comparing them with my own measurements. Since I did not see any major deviation in the values, I concluded that the components were generally in good condition. I also did not see any burned, deformed, or otherwise damaged parts.

After all this, I first focused on the board on the bottom side of the unit. This board contained the DC power input, audio (microphone) input and its amplifier, the transmitter, the 10 MHz reference oscillator, and the tone oscillator. The work I did regarding these circuits was as follows:

• First, I readjusted the 10 MHz reference oscillator (there was a drift of about 200 Hz). For this, we connect the frequency counter to test point TP108 and use trimmer capacitor C144.
• I replaced the electrolytic capacitors at the DC input (after 40 years of service, it was time for the old ones to retire).

Heathkit HW-2036A Transmitter Board. 
The bad screw is the one at top-right of the picture.

Heathkit HW-2036A Transmitter Board - After replacing
the electrolytical capacitors.

Layout of the board: The section with 5 ICs at the top left is the 10 MHz oscillator,
below it is the tone oscillator (and its trimmer resistors), and at the bottom left is
the microphone amplifier. The right side of the board is the transmitter.
The center is DC power section.

Microphone Repair (Micoder-1)

• I opened up the microphone (Micoder version 1) and ran some tests, and I found that when I cut the supply to the DTMF circuit inside, both that strange tone disappeared and I could hear my own voice normally from the other end. I removed the DTMF circuit and ran it independently. I took measurements and compared the results on its schematic with the reference values. During my tests, I realized that this circuit was producing tones correctly, but the flexible keypad used to command the circuit had gone bad. Because the bottom two rows of the keypad were in constant contact, the circuit was producing a corrupted signal when PTT was pressed. Since I had no chance of finding another copy of the same keypad, and I also wanted to preserve the original appearance of the microphone, I reinstalled the DTMF circuit with its supply point inside the microphone disconnected. We don't really need DTMF tones much these days anyway. No repeater is connected to telephone lines anymore; only repeater trustees use these tones to manage the equipment at the repeater site. So there was no need to insist on the repair either. I closed the microphone with the microphone capsule powered.

Working on the microphone (Heathkit Micoder-1). The tone circuit works normally when separated from the keypad and the contacts are shorted by hand. Unfortunately, finding a new or used copy of the same keypad is very difficult.

Heathkit Micoder-1 Microphone. The bottom two rows 
of the keypad you see here are short circuited. The
structure of the keypad does not allow repairs.

Powering the Microphone Capsule Without a Battery

• I did not want to use a battery to power the microphone capsule. I barely talk for 5 minutes once a month anyway, if at all. For that reason, I also didn't like the idea of leaving a battery that could leak inside the microphone. So, as suggested by W9RAS, I made the shield of the microphone cable the negative conductor and soldered it to a chassis point on the unit. I then connected the negative conductor in the cable to a 12V point on the unit, thus providing the required power to the capsule.

The black wire soldered to the slide switch inside the microphone now carries 12V;
the other end of this wire is soldered to the blue wire at the top left corner of the photo.

Transmitter Output Alignment

• After all this work, I readjusted the output stage to bring the output power back to 10W. Since the manual provides these adjustments in detail, I don't feel the need to repeat them; I will only give the main outlines and the key points below. First, I disconnected plug J102 going to the final amplifier at the output and connected a 50 Ohm dummy load, then measured the voltage at the sampling points from TP101 to TP104 and readjusted the adjustable coils from L101 to L107 (I also did this adjustment by looking at the signal amplitude at the final stage on the oscilloscope, but doing it with a voltmeter with high input impedance (10 MΩ) is more practical). Here, L105-L106-L107 in particular make things take a bit longer since they affect each other. Fortunately, Heathkit's manual explains in detail how all these adjustments are to be made... In the end, I reached 10 Watts of power at the transmitter's set frequency (147.010). Since 10 Watts is the specified power for this radio, I did not tamper with the output stage to try to get more.

CTCSS Tone Configuration

• After making sure the transmitter was working properly, I wanted to transmit with a tone to access the repeaters in my area. The tone circuit has 3 "legs" set up to produce 3 different tones, and each leg has miniature trimmer resistors that need to be adjusted for tone setting... However, I noticed that no signal was coming on any of the 3 tone options. After some troubleshooting, I realized that all of the fine-tuning potentiometers used to adjust the tones were in the "zero" position. The late amateur who assembled the unit had probably never needed a tone. As soon as the resistor settings were changed, I started seeing the tone on the frequency counter. I adjusted the 3 tones that would be most needed for me.

Cleaning Oxidized Contacts

• Let me also mention one procedure I performed not only on the transmitter board, but on all three boards. I lightly scraped the legs of all integrated circuits and the metal (contact) surfaces of all connectors with a utility knife, cleaning off the layers that had formed.

Notice the legs of the integrated circuit—there is some oxidation, even if slight.

I'm covering it all on a single page here, but what I described above took approximately from August to October. After taking care of the transmitter, it was the receiver's turn. You can read the rest of the article [here]

Also: I have explained the details of this restoration in 4 parts on my Youtube channel as well, you can watch it here.

Frequently Asked Questions

What are the common problems found in a used Heathkit HW-2036?

Common problems include low transmit output power, a deaf receiver with poor squelch sensitivity, a non-functioning S-meter, burned-out illumination lamps, muffled audio, and aged electrolytic capacitors. Mechanical issues such as freely spinning screws caused by improperly tightened standoffs can also prevent access to internal boards.

What screw size does the Heathkit HW-2036 top case use?

The top case screws are 6#-32 (American standard thread size).

How do you adjust the 10 MHz reference oscillator on the HW-2036?

Connect a frequency counter to test point TP108 and adjust trimmer capacitor C144 until the oscillator reads the correct frequency.

How do you adjust the HW-2036 transmitter output to 10 Watts?

Disconnect plug J102 going to the final amplifier and connect a 50 Ohm dummy load. Measure voltage at sampling points TP101 through TP104 and adjust coils L101 through L107 accordingly. A high-impedance voltmeter (10 MΩ) is more practical than an oscilloscope for this. Note that L105, L106, and L107 affect each other, so the adjustment requires patience.

What is a possible issue with the Micoder version 1 microphone on the HW-2036?

In my case, the DTMF circuit inside the microphone had a deteriorated flexible keypad, causing the bottom two rows to remain in constant contact. This produced a corrupted signal and a strange tone when PTT was pressed, also making the transmitted audio sound muffled. Disconnecting the DTMF circuit's supply resolved the issue. Since DTMF tones are rarely needed today, the circuit was left disconnected while preserving the microphone's original appearance. 

How can you power the Micoder microphone capsule without a battery? 

As suggested by W9RAS, the microphone cable shield can be repurposed as the negative conductor and soldered to a chassis point on the unit, while the original negative conductor in the cable is connected to a 12V point on the unit to supply power to the capsule. 

Why might the CTCSS tones not work on the HW-2036? 

The tone circuit has three legs, each with miniature trimmer resistors for tone adjustment. If the unit was originally assembled without configuring these tones, the trimmer potentiometers may be left at the zero position, producing no tone output. Adjusting these trimmers while monitoring with a frequency counter will restore tone functionality.

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

My videos on the restoration of HW-2036, part 4: 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

Heathkit HW-2036 VHF Transceiver Restoration - Part 1

In brief: This post is the first of a 3-part series about the restoration of a Heathkit HW-2036A, a PLL-controlled, 10-watt, 2-meter FM transceiver from 1976 that I picked up for almost nothing at a flea market in Montreal. In this part, I cover the history of Heathkit's VHF radio lineup and how the HW-2036A works under the hood. The following parts will go into the problems I found and how I fixed them. 

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. 

Heathkit HW-202 - Crystal Controlled (1973)

Heathkit HW-202 from Heathkit 1978 Catalog

Heathkit 2026 - Synthesized (1975) 

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.

Heathkit HW-2036 (1975)

Heathkit HW-2036 in 1978 Heathkit Catalog

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) 

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

WB2CBA USB Sound Card Based Digital Interface and Vox for Digital Modes

In brief: The WB2CBA design CM108AH-based USB sound card VOX circuit enables the use of FT8, FT4 and WSPR modes on QRP radios such as the uSDX that lack a CAT interface. 

This article covers the installation of the WB2CBA (Barbaros Aşuroğlu) designed USB sound card VOX circuit with a CM108AH-based external sound card, and its use with the uSDX QRP radio in WSPR mode. This low-cost and easy-to-build circuit, intended for those who want to use digital modes such as FT8, FT4 and WSPR on radios without a CAT interface, automatically handles PTT control based on the signal level at the computer's audio output. The circuit schematic, parts list, elimination of ground loop and PTT voltage problems, and a WSPR performance comparison between 200 mW and 5 W are among the main topics covered.

WB2CBA Interface for Digital Modes as I built in on a perforated board

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WB2CBA's Sound Card-Based Digital Interface VOX Circuit

There is almost nothing I can say about this circuit — other than the fact that it works very well and is very easy to build. You can find extremely detailed explanations about both the construction and operation by its designer, Mr. Barbaros Aşuroğlu (WB2CBA), on the electronics projects pages of the Antrak website. The circuit consists of a USB sound card designed to be plugged into computers via USB, along with a few components to connect it to the radio through its audio input and output connectors. It is an extremely economical solution for operating in digital modes with radios that lack CAT control — such as the uSDX or your own homebrew QRP radio.

I am not particularly fond of digital modes myself — especially modes like FT4 and FT8, which cannot be considered real two-way conversations, bore me. It is a matter of taste and preference, but these techniques feel to me like they require no operating skill, and I feel useless. As I have noted in other posts, if something doesn't require work, learning, and effort, it holds no interest for me. So I don't use these modes for actual communication — with one exception: WSPR. When I built this circuit, my intention was not to do FT8, but to operate WSPR with the uSDX.

I had actually been running my WSPR transmitter on and off for a few years, but there were two things I was curious about: what would happen if I increased the output power, and if I also received instead of just transmitting, how many stations would I be able to hear. I decided to build this circuit to connect to my uSDX and try it out. I was curious where I could reach by going from 250 mW up to 5 W. And how many of the stations that heard and decoded my signal would I in turn be able to hear?

Also designed by WB2CBA, this is my WSPR transmitter.
It connects via WiFi to my home modem, syncs the time
 from a server over the Internet, and transmits a message every 4 minutes

Components and Construction of the VOX Circuit

There isn't much to say about the construction. If you look at the schematic above, you will see that the components are extremely easy to source. The only part you need to specifically seek out is the USB sound card built around the CM108AH integrated circuit. I used the type whose photo you will see below — you can get this online for 3–4 US dollars including shipping. Mr. Barbaros has also designed a PCB to mount this sound card on, but I made the connections on perforated board in a layout similar to his. It obviously didn't turn out as elegant as a proper printed circuit board, but it does the same job.

WB2CBA Digital Interface Schematic

The CM108 USB Sound Card I used for this project

WB2CBA Interface for Digital Modes as I built in on a perforated board

Post-Build Operation, Tips, and Solutions to Some Possible Problems

What the circuit does is cause the radio to switch to transmit when a signal of a certain level is detected at the computer's audio output. It does this by amplifying and rectifying the signal and applying it to the gate of a FET transistor. The transistor, connected to the radio's PTT input, short-circuits the transmit and ground lines when it conducts. A red LED lighting up at the same time shows us that "PTT has been pulled to ground." In the other direction, the audio signal coming from the radio passes through a variable resistor before entering the computer. It sounds simple, but after assembling it I couldn't get it working right away and struggled for a while. Let me summarize the reasons:

• The positive voltage at the uSDX's PTT pin could not be pulled fully to zero for a reason I couldn't understand (it was staying around 0.2 V) and the transistor couldn't conduct. I couldn't resolve the problem until I added a diode to block the voltage coming from the radio into our circuit. Note: this diode is not in the original schematic, and when I asked Mr. Barbaros about it, he said he hadn't needed to make such an addition. So the problem may be specific to my circuit or my connections to the radio.
• After that problem was resolved, another situation began to emerge: when I plugged in the connector coming from the circuit into the radio's audio output, the transistor would start conducting and put the radio into transmit. I resolved this too by adding a diode to the end of the cable coming from the radio. I believe the problem is ground-related — probably a ground loop forming, with current flowing somewhere it shouldn't. The cleanest solution would be to use an optocoupler between the VOX circuit and the radio to break the electrical connection, but it must be remembered that this circuit was designed to be simple by nature. If we can get it working with two diodes, we'll stick with that. :)
• The third problem I encountered was on the software side. Through trial and error I realized that the level of the audio signal coming out of my computer wasn't sufficient to drive the transistor into conduction. No matter how much I adjusted the computer's audio settings, I couldn't solve the problem. I eventually realized that in the WSJT-X software I was using, it isn't possible to raise the level sufficiently using the vertical slider on the right side of the interface without adjusting it. I left that setting at the lowest point at which the radio switches to transmit. I should also mention something about the receive level setting: it should be set to 30 dB with no antenna connected to the radio.

The diode I had to insert between the transistor's drain pin and the radio

Finally in operation - stable now

The input level on the left needs to be set to 30–40 dB, and the output level
on the right should be left at the lowest point at which the radio switches to
 transmit when pressing the 'tune' button just above it.

Conclusions and Some Observations

I used the circuit I built this way in WSPR mode for a while (and even did a bit of FT8 and FT65). What I found:

• Despite the large 14 dB difference between 200 mW and 5 W output power, I didn't see a very large difference in the distance of the stations that heard me. To give an example from the eastern direction: at 200 mW I was heard at most from Austria. At 5 W I was heard from Italy, the Balkans, and once from Turkey.
• The number of stations I could hear was, as I expected, far fewer than those I could reach. I wasn't expecting more than that anyway, with a 10-meter wire strung from a first-floor window to the garage awning.

These results once again confirm what is already known:

• Unlike modes such as SSB and AM, with CW or — if you like them — digital modes, you are always heard from farther away.
• Instead of higher power (100 W and above), it is better to invest in a better antenna.

One final point: to operate in the digital modes mentioned above, your computer's clock must be accurate. If you use WSJT-X as I do, you will also need software that periodically connects to a server over the Internet and re-synchronizes your computer's clock. I used BktTimeSync for this.

A wonderful circuit for those who want to get into digital modes with an inexpensive and enjoyable build. I wish success to the amateurs who try it, and once again extend my thanks to Mr. Barbaros.

FAQ — Frequently Asked Questions

1. What does the WB2CBA USB Sound Card VOX circuit do? 

Simply put, it allows the computer to communicate with the radio. When the audio signal from the computer reaches a certain level, the circuit automatically switches the radio to transmit. It stands out as one of the most practical and inexpensive ways to use digital modes such as FT8, FT4, or WSPR on radios without a CAT interface — such as the uSDX or a homebrew QRP radio.

2. Which USB sound card should be used? Is the CM108 mandatory? 

The design is based on the CM108AH chip, and cards with this chip can be easily found online at very low cost.

3. The PTT voltage won't go to zero and the radio won't switch to transmit — what should be done? 

This problem is encountered particularly with the uSDX: a residual voltage of around 0.2 V remains at the PTT pin and the transistor cannot conduct. The solution is surprisingly simple — adding a single diode between the radio and the transistor's drain pin is sufficient. This diode is not in the original schematic, but it has been found to work when this voltage problem is encountered.

4. The radio switches to transmit as soon as the audio cable is plugged in — what causes this? 

Most likely a ground loop problem is occurring. Current is flowing somewhere between the radio and the computer where it shouldn't be. Adding a diode to the end of the cable coming from the radio resolves the problem. For a more permanent and cleaner solution, using an optocoupler could be considered; however, since simplicity is at the heart of the circuit's design, sticking with two diodes is reasonable if that gets the job done.

5. The audio level in WSJT-X is never sufficient — what should be done? 

Opening the horizontal slider in the interface all the way usually isn't enough. The vertical slider on the right should be left at the lowest point at which the radio switches to transmit. For the receive level, 30 dB with no antenna connected is a good starting point. It requires some trial and error, but once found it stays stable.

6. Which radios does this circuit work with? 

It is expected to work with any HF radio that has a PTT input. The primary target audience is radios without CAT control — uSDX, homebrew QRP radios, and similar models. If a commercial radio with a CAT interface is being used, controlling PTT through software is a more practical approach.

Links

WB2CBA's original article: Click here

BktTimeSync download: Click here

WSJT-X download: Click here

Kent Iambic Paddle Kit Review: Build Quality, Feel, and CW Experience

Kent dual-lever paddle is a classic iambic key designed for CW (Morse code) operators in the amateur radio world. In this article, the structure of the kit, the assembly process, and its usage features are discussed. In particular, the advantages it offers in terms of precision, ergonomics, and response time in CW communication are examined, explaining why it is preferred by both beginners and experienced amateur radio operators.

Bu yazının Türkçe'sine ulaşmak için tıklayınız.

Why did I start looking for a dual-lever (iambic) paddle?

When I first started amateur radio, I was very interested in learning radio telegraphy (CW), something I had admired for years but never had the opportunity to seriously pursue. This year, I finally found the chance to do so. Over three months, I attended the “CW Academy,” offered online for free by CW Ops club volunteer instructors, and was able to bring my telegraphy skills to a beginner level.

When I started this course, my intention was to use a single-lever “straight key” paddle that I had built myself. However, after seeing one of the recommendations—“if you are seriously going to work CW, get used to a dual-lever paddle from the very beginning”—I borrowed a Bencher BY-2 paddle from a club friend and continued my lessons with it. As a side note, this brand has been around for 45 years but continues its life under the Vibroplex brand. In North America, this is probably the most commonly seen paddle; you can often find them at flea markets for around 50–60 USD.

QST, May 1978: Bencher paddles have been manufactured 

since 1977, based on the design by W8FYO.

Bencher: the most established fixture of all flea markets

My opinion about this paddle, which I used almost every day for three months, is that it is a very difficult paddle to adjust. I don’t want to go into a long explanation, but as you can also see on IW5EDI's page, the contact points are not on the sides like in other dual-lever paddles; instead, they are at the front, working through sharp-pointed screws at the ends of spring-loaded “elbow” shaped arms that move slightly back and forth into corresponding slots. To adjust this mechanism, you need to tighten or loosen the screws that control both the spring tension and the position of these elbow-shaped parts. To set the contact gap, you also have to rotate two screws clockwise or counterclockwise. No matter how much I tried, I could not achieve a configuration that felt comfortable, and overall I did not find this paddle very usable.

On the other hand, the three months I spent with the Bencher also helped me clarify what I expect from this type of paddle. I decided that the following four features are my priorities:

• Smoothness in the mechanism: being able to translate finger pressure into contact without requiring excessive force or abrupt movements, and having fast return of the levers
• Quick and easy adjustability: being adjustable even during a contact if necessary is a plus
• Durability: since it is a relatively expensive piece of equipment, it should have reasonable build quality and the ability to find spare parts
• “Stability” / footprint: when using the paddle, it should be heavy enough not to move on the desk, but not so large that it takes up too much space

Kent Paddles Versus Other Alternatives

As I was nearing the completion of the course, I started looking for a paddle online as a kind of reward to myself. I ruled out some brands despite their quality (such as Begali) because they were above my budget, and I set aside smaller “field-type” paddles (for example Bamatech). In the field, a simple paddle made from 3D-printed parts would have worked perfectly well. When I ranked the remaining candidates by user count and positive review ratio, not many options were left. I first leaned toward an American paddle that looked attractive in terms of price (AMM), but the shipping cost was almost as high as the paddle itself, so I slightly increased my budget and decided on Kent Engineers’ dual-lever iambic paddle.

Although Kent is originally a British manufacturer, after the United Kingdom left the EU, it moved to Germany in order to maintain tax and logistics advantages. As a result, the paddles are now produced in Germany and shipped to you via DHL. All parts of the paddle are brass, while the base is steel. Since the levers sit on bearings, friction is very low. Although springs are used for return action, the response is fast, and overall the mechanism feels smooth and comfortable to use. The contact points are silver-plated. There are no adjustments other than contact spacing and lever tension, and these are made easy to adjust using large knurled screws, so you don’t need any tools like screwdrivers or Allen keys. Additionally, the left and right sides can be adjusted independently.

Another advantage of purchasing this paddle is that you can choose to buy it as a kit and assemble it yourself. I preferred the kit version because I was curious about it, it reduced the risk of customs issues, and it also lowered the cost slightly. The package arrived about three weeks after placing the order. Since no special adjustment was required, I completed the assembly in about an hour. I have been using the paddle with my own keyer now and I am very satisfied with it; I will most likely continue using it for many years.

The completed assembly; I later installed the bakelite parts
on the levers with their tips facing downward.

FAQ

1. What is an iambic paddle?
An iambic paddle is a dual-lever key used in CW (Morse code) communication. It allows dots and dashes to be generated in a fast and rhythmic way.

2. What does “iambic” mean?
The word “iambic” comes from a poetic rhythm term and refers to a weak-strong stress pattern. In Morse usage, it represents rhythmic signal generation.

3. How does an iambic paddle work?
One lever produces dots (dits), the other produces dashes (dahs). When both levers are pressed at the same time, the device automatically alternates dots and dashes.

4. What is the difference between an iambic paddle and a straight key?
A straight key produces signals manually with a single lever. An iambic paddle works with an electronic keyer, enabling faster and more consistent sending.

5. What are the advantages of iambic keying?
It provides less hand fatigue, higher speed, better timing accuracy, and more efficient Morse sending.

6. Is an iambic paddle suitable for beginners?
Yes, but it requires some practice to get used to. Once learned properly, it offers more efficient operation in the long term.

7. Does an iambic paddle require additional circuitry?
Yes. An electronic keyer (Morse keyer) is usually required for proper iambic operation.

Links

Kent Morse Keys - Manufacturer's Web Page: click

GW6ITJ's review: click

Another review: click

Adding a 3.5 mm jack to Kent Iambic Key's base: click

IW5EDI's excellent page on Morse key adjustments including Bencher: click

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