SA2CLC radio stuff

 I needed to knock down the second harmonic from my amplifier as I was getting spotted on 20 when conditions were good, when calling CQ on 40 using my multiband vertical. At first I was thinking about some sort of low impedance, series resonant circuit on 20, installed between vertical feedpoint and ground, but then I shifted to coax stubs, but I had no SO239 tee's. I wanted to it done right away so I figured I'd install panel mount SO239's on an aluminum box, and make the stub connection on the inside, when I read about W2VJN's hybrid lowpass filter. It's a three pole lowpass, but instead of capacitors, it uses coaxial cables with their ends open. Since they need to be left open, they are cut to 1/4 wave on the frequency that we want to supress. For 20M, this works out to be approx 3,4M.  The series coil is about 1uH to resonate with the coax capacitance. I built this because it was an easy design, and no more work than to drill 4 holes in a 1590B box. I used, afte...

A Small Utility: F-Key Router for keyer programs When operating CW, function keys quickly become muscle memory. Most logging software maps F1–F12 to macros — CQ messages, exchanges, TU, QRZ and so on. The problem appears when the logging program does not have focus . You might be typing in another window, checking cluster spots, or adjusting some other software. Pressing an F-key then does nothing for the cw keyer, because the keystroke goes to the active window instead. To solve this I wrote a small Windows utility: F-Key Router . The program listens for function key presses and forwards them to a selected application window , regardless of which program currently has focus. What the Program Does The program is intentionally minimal. It does only three things: Select the target window (for example Log4OM , N1MM , or another logging program) Start listening for F-keys Forward the keypress to that window This means you can press: F1 for CQ F2 for exchange ...

Handling negative voltages and getting boards sponsored by PCBWay PCBWay supplied the PCBs for this project as part of a collaboration — my write-up here is focused on the technical aspects of the design and build. The problem  In the amplifier project, I need to measure currents and voltages. Plate voltage (Ua), plate current (Ia), screen voltage (Ug2), screen current (Ig2), control grid current (Ig1) and also control grid voltage (Ug1). My first approach failed due to me not thinking properly. The current measuring relies on shunt resistors, which is a proven and reliable way to measure dc current. A resistor is placed in a branch of the power supply and by measuring the voltage drop across the resistor we can calculate the current, using ohms law, I=U/R.  Upon testing the amplifier I realised that the arduino would not measure any current. Voltage measurment (Ua, Ug2) uses voltage dividers, and that worked as planned.  Eventually it dawned upon me that I was trying to ...

Elecraft K3 – Rear mic jack not working I recently decided to upgrade the headset in my “modern” station. Although my Heil Pro headset has been working fine, it becomes uncomfortable during longer operating sessions. At Mike (SJ2W), Bose QC25 headphones combined with Antlion ModMics have been used for many years. After working a few contests there, I can confidently say they are much more comfortable than the Heil headset, and way cheaper, since these headphones and mics are widely used by gamers. I picked up a used Antlion ModMic and a pair of Bose QC25s, and with that I wanted to clean up the wiring a bit—specifically getting rid of the bulky Heil “K” adapter with its large 1/4″ ptt jack on the front panel.  Since I only use a footswitch for ptt I felt it was annoying to have it cluttering the desk. My plan was to use the rear connectors for audio on the Elecraft K3, since there are plenty of them. Line in, Line out, phones, mic, and speaker output.  Unfortunat...

 I got a trailer full of transmitter delivered in september. A transmitter built to order by one of the "Big guns" back in the 1950's, SM5RM. It was probably built by SM5LI around 1951, who at the time worked at Standard Radio in Bromma. Standard Radio was a swedish manufacturer of radio equipment, known for the military CT-450, RA200, SSA400, and amongst others the CR300 series of receivers. The build quality is exceptional. Everything is heavy duty. High quality components from the SRT production line is used, and all of the chassis parts are beatifully crafted, panels are engraved etc. Not that I needed another project, but hey, you can't pass 400lbs when it's being delivered to your doorstep. Transmitter before it was taken apart for shipping The transmitter sports 2x813 in push-pull in the power amplifier. Modulators are also 813's. There is a 2M transmitter in the rack as well as an antenna tuner, fully metered etc. The power supply contains a big oil fi...

  A directional coupler for the amplifier. In this post we take a look at the directional coupler I built for the amplifier. I wanted a built-in coupler to measure power and have SWR protection. I built a tandem match coupler. Why, you might ask? Because I’ve built one before with good results, and after struggling with a Bruene coupler design(which I could never get to work properly), I decided to stick with what I know works. Schematic representation of a tandem match. The transformers are wound on ferrite toroids where the primary is one pass of coax thru the center. Note that the turns ratio needs to be the same for the transformers, even though the cores may differ. Theory in brief (with disclaimer) Expect no in-depth math here. This is a simplified explanation and more of a picture series on how I built mine, along with some thoughts on how to improve it. A tandem match coupler works by sampling both current and voltage in the transmission line using transformers: T...