Elecraft W1 SWR/Wattmeter Kit

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.

SignaLink USB Noise Floor Mod

The SignaLink USB is one of the most common external sound card interfaces for digital modes in ham radio. It has a lot of good features and overall is a very useful piece of equipment. It also has a high noise floor as shipped from the factory which can inhibit the sound card’s ability to decode week signal stations as effectively as it should.

Due to the SignaLink’s use of unregulated USB power to drive its amplifier circuits, not only is the internal noise floor higher than it could be, it also varies from computer to computer. Fortunately, there is a very simple mod that resolves this limitation which was printed in the August 2014 issue of QST magazine.

The mod involves removing one surface mount resistor from the circuit board and installing a new resister between two other connection points on the board.

The results of comparing the noise floor before and after performing this mod are pretty striking, with between a 10 and 30 dB lower noise floor depending on how noisy the 5V USB power supply is. As you can see in the comparisons shown below, the low frequency noise is greatly reduced as is a significant birdy at around 1000 Hz. This also demonstrates how different two 5V power sources can be with the PC much cleaner than the USB hub.

Test 1 – Shack PC Power

Test 2 – USB Hub Power

This is about as easy of a mod as can be done on a piece of electronics and I highly recommend doing this if you use a SignaLink USB for low signal work.

Elecraft KX3 Station Accessories

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

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.



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).


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.


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.

Baluns & Ununs

Anyone building antennas will come across designs that either recommend or require the use of a balun or unun. The design and construction of these components can get quite complex and are beyond the scope of this blog and my own knowledge. In short these devices act as impedance transformers from balanced loads to unbalanced loads (balun) or from unbalanced loads to unbalanced loads (unun). They can also be used as a common mode choke to eliminate any RF on a coax feed line’s shield. That said, it is actually quite easy to construct your own baluns and ununs and to learn something in the process. You can also save a considerable amount of money.

1-1 Balun (2)1-1 Balun (1)Amidon sells a good starter kit for building baluns and ununs. It includes everything you need including a book with dozens of designs with various impedance transforming characteristics. 1-1 Balun (6)1-1 Balun (3)I used this kit to make a 1:1 balun. Since the kit uses 14AWG wire, it should be capable of handling 2KW of power continuously. This is overkill for me since I will never be putting more than 100W through the balun. The 1:1 balun is essentially a choke that blocks current flow on the shield of the coax feed line. It is constructed using 10 bifilar wraps on the toroid core using approximately 4 feet of wire.

For other projects I decided to use the same FT-240-K core with 18AWG wire covered in 16AWG PTFE insulation. While the 18AWG has less power handling capability, it should be more than adequate for 100W usage as well as being cheaper and easier to work with.

4-1 Balun (2)4-1 Balun (1)The first balun I made using these materials was a 4:1 current balun. This balun is intended to transform a 200 Ohm load for use with a 50 Ohm coax feed line. This type of balun is commonly used in 4-1 Balun (3)Off-Center-Fed dipole antennas because the feed-point is placed at the location on the antenna where the impedance is approximately 200 Ohms on multiple bands. I intend to use this balun as part of a 6 meter collinear antenna that I am building. The balun is constructed using two sets of 8 bifilar wraps on the toroid using approximately 8 feet of wire. Each pair of windings is then wired in series with the other pair. This design can be thought of as two 1:1 baluns wired in series and in fact an alternate design of this balun uses two separate 1:1 balun cores wired in series to achieve the same affect.

9-1 Unun (2)9-1 Unun (1)Next I made a 9:1 unun for use with an end-fed antenna I am building. End-fed antennas exhibit very large impedances and consequently require considerable impedance transformation to 9-1 Unun (3)get the feed point within the range of an antenna tuner. Unlike a dipole, an end-fed antenna is unbalanced and therefore an unun is used instead of a balun. This design uses 8 trifilar wraps on the toroid using approximately 6 feet of wire. Each wrap is then wired in series to create the desired impedance transformation.

1-1 Line Isolator (2)1-1 Line Isolator (1)I also made another 1:1 balun. The main difference here is that I constructed it using two SO-239 connectors because I intend it to act as a coaxial feed line isolator. My plan is to use this in conjunction 1-1 Line Isolator (3)1-1 Line Isolator (4)with the 9:1 unun as part of my end-fed antenna project. The idea here is that a section of coax from the 9:1 unun acts as the counterpoise for the end-fed antenna and the line isolator is used to choke the RF current in the shield of the coax and allow the remainder of the feed line to continue to the antenna tuner without risk of radiating RF.

For all of these projects you can see that I used colored electrical tape to mark the various windings. This is essential to keeping track of the wiring and assuring that the windings are wired together correctly. For all of these I also used standard NEMA 4X 4″x4″x2″ plastic electrical boxes which are cheap and commonly available. I also used 10-32 stainless steel hardware for the antenna connections and silver-teflon SO-239 connectors.

PSK31 Sound Card Interface

psk_interfaceIf your sound card has Line In and Line Out jacks, and your radio has an accessory port, this is the easiest way to interface between the two. Using your radio’s accessory port eliminates the need for more circuitry to control the audio level going to and from your radio. This interface has worked perfectly during regular use and several Field Days. All the parts are available from RadioShack, and it can be constructed in under an hour.