Accessories

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Elecraft W1 SWR/Wattmeter Kit - February 24, 2020

I like building my own radio equipment and I’m always on the lookout for an interesting kit to build that would be useful for my station. What caught my eye about the Elecraft W1 SWR/Wattmeter was the fact that it covers 150mW to 140W power levels, making it equally useful for QRP as well as in a typical 100W HF station.

The kit uses through-hole components and is straightforward to build. The provided instructions are very well done and step you through every part of the assembly process. The trickiest part of the build is the SWR bridge binocular toroid, which can be finicky to wind, but if you take your time it is not a problem.

As with all Elecraft gear it is not the cheapest option out there at $130, which doesn’t include a case. I considered trying to retrofit my own case for the meter, but in the end I purchased the W8FGU case. The case is well made and easy to assemble with various options depending on how you want to arrange the meter’s coax connections and circuit board. I opted for the straight BNC coax connector option. This places the coax connections on the back of the case instead of the sides and works much better for cable management in my station. Instead of purchasing the tilt base option for the case I built a simple wooden base with angle brackets bolted to a piece of lexan. The case is attached to the lexan using super heavy duty velcro squares (for easy removal of the meter) which results in a very stable assembly that doesn’t slide or fall over from the weight of the coax cable connections.

The meter is very simple to use and reads both forward power and SWR simultaneously, each on their own LED strip. Three separate LEDs indicate which scale of power the meter is reading, 0-1.4W, 1.4-14W, and 15-140W. The LEDs are bright and make it very easy to read the meter in any lighting condition. The benefit of the bar-graph style of the meter is especially noticeable when using a manual antenna tuner since the dip on the SWR display when you find a match is much more obvious to the eye than with an equivalent cross-needle meter.

The meter can be powered by a 9V battery or an external 12V power source, and the case includes an external power switch. As is typical for Elecraft equipment, the W1 has a lot of additional functionality built in. The meter has a serial port (via a 3.5mm jack) and the various settings (decay, peak hold, etc.) can be adjusted using a serial terminal or with a piece of software from Elecraft that can also display the meter’s readouts on your computer screen. Overall a great kit.

Elecraft KX3 Station Accessories - September 1, 2018

Earlier this summer I purchased an Elecraft KX3 to use as a portable radio as well as my main station radio when paired with my Hardrock 50 amplifier. To facilitate both of these scenarios I had to make a couple of accessories to adapt my existing gear to the KX3.

The KX3 has several 3.5mm and 2.5mm jacks on its left side for the microphone, headphones, accessory connections, RX I/Q data, etc. Since the mic jack is the only way to get audio into the radio and I operate both voice and digital interchangeably quite often, I didn’t want to have to unplug the mic connection every time I changed modes. To solve this problem I built a microphone connection switch box. The box allows for the connection of a common 8-pin round microphone plug (in this case wired to the Kenwood/Elecraft wiring convention) as well as a 3.5mm jack for the output of the sound card I use for digital modes. The two are switched via a DPDT toggle switch and connect to the KX3 with a TRRS 3.5mm right angle plug. Both connections also feature 0.1uF DC blocking capacitors and the sound card side includes a 10:1 voltage divider which results in a 20dB reduction of the sound card output. This allows for much easier control of the audio going into the radio and helps prevent over-driving of the mic input. The blocking capacitors were intended to prevent any mic bias voltage from affecting my dynamic desk microphone, however, I found that some still got through. To solve this issue I made some macros for the KX3 to switch between desktop voice, digital, and portable voice configurations. This allows me to turn the microphone bias on or off and adjust the mic gain and compression depending on whether I am using the desk mic and foot switch in my station or a handheld microphone while portable.

The other accessory I made is for portable digital operation. I wanted to keep my setup as compact and light as possible, so I wanted to avoid having to take my SignaLink USB with me in the field. I found a good compact USB sound card, but I wanted to add some isolation from the radio as well as some signal reduction from the sound card output to the radio similar to what I did in my microphone switch box. For isolation I used ground loop isolators to reduce the possibility of interference between the radio and the sound card. To reduce the sound card’s output I used another 10:1 voltage divider to reduce the output by 20dB. In this case I only did it to the left channel since this is the default used by most digital programs and it is the same position on the 3.5mm mic jack as the microphone input on the KX3. Fortunately I was able to install the voltage divider inside of the isolator case itself by carefully prying apart the two halves. The voltage divider resistors were then soldered directly to the isolator circuit board and fit inside the case with plenty of room. The isolator case snapped back together when I was done modifying it without any glue necessary.

So far my KX3 accessories have been performing well and they make an already great little radio that much easier to use.

Boafeng UV5R USB Soundcard Interface - February 17, 2017

I recently purchased a Baofeng UV5R5 to throw in my Go Kit as a backup handheld and I decided to build an interface to be able to send and receive digital signals. The interface was intended to be as simple and inexpensive as possible, much like the radio itself.

VHF/UHF digital EMCOMM transmissions in my area typically use the MT63 mode which is very robust and can work quite well using only acoustical coupling. While this technique works surprisingly well, it has limitations. If the area you are operating in is too noisy, your audio is too weak, etc. the data transmission can have issues getting through correctly. It also doesn’t work very well for modes other than MT63.

USB soundcard interfaces are very common, I have multiple SignaLink USBs myself, but they are definitely overkill for this application. After some experimentation, I built this simple interface for under $20.

Parts

• SYBA USB Soundcard

• 3.5mm Male-to-Male Stereo Audio Cable

• Baofeng UV5R Speaker Microphone

Construction

The main idea for this project was to replace the external speaker microphone functionality with that of the USB soundcard. In order to do this I used the speaker mic cable and wired it to two 3.5mm stereo audio cables such that the speaker output from the radio connects to the microphone input of the soundcard and vice versa. Each splice was soldered and insulated with heat-shrink tubing. The entire joint between the three cables was then secured with more heat-shrink tubing. Each 3.5mm plug was marked with colored electrical tape to make it easy identify which cable plugs into which port of the soundcard (red for microphone, green for speaker).

Operation

To operate, I plug simply plug in the cables and connect the USB soundcard to my computer (a big advantage of this model of soundcard is that it does not require special drivers for Windows 10 or Linux, it is truly a plug-and-play device). When I am ready to send data I simply key the radio using the PTT switch on the side and click the transmit button in the digital software. When the transmission is finished I unkey the radio. I had originally played around with an external VOX circuit as well as the UV5R’s internal VOX feature, however, neither of them would reliably key the radio and stay keyed throughout an entire data transmission and I decided they were unnecessary. Using manual keying is actually somewhat of an advantage since it simplifies the interface, reduces complexity, and doesn’t require changing the radio’s configuration.

Calibration

I used FLDIGI to test the interface over simplex to another radio. After some experimentation I found that with the radio’s speaker volume set at a comfortable level (about 1/4 turn) a setting of 50% for the soundcard’s microphone gain was a good audio level for receiving data. For transmitting, I found that a setting of 1% from the soundcard’s speaker produced the cleanest output.

If I was going to build more of these I think I would add a 10K ohm resistor at the connection between the soundcard’s speaker output and the radio’s microphone input. This would attenuate the signal somewhat and allow for finer control over the transmit audio level. Even so, as it stands now the audio is clean and data transmission worked flawlessly. I have used this interface on my local digital net and it performs very well. This has definitely found a place in my Go Kit.

Update (March 2017)

I recently discovered that FLDIGI has a built in TX Audio Attenuator feature. Using this I can achieve much finer control over my transmit audio level, even with the soundcard’s speaker output set to 1% volume. This makes adding a resistor in the transmit audio wiring unnecessary.