New Project: QRP Transceiver (Update #1, February 21, 2020)

Recently I’ve taken up a new project – I am building a QRP transceiver for 40m, CW only. The intention is to have a small radio, 5 watts or so, which I can carry almost anywhere and operate easily. Also, it must be completely scratch built by me. I decided on 40m as I already have a 4SQRP Hilltopper for 20m, as well as a QCX also for 20m.

I decided on a design using an Arduino Nano(well, a clone) as the heart of it along with an Si5351 for the VFO. This section I completed first on a breadboard, and then soldered down. I wrote all of the code for this from scratch. The Si5351 produces an output between 7MHz and 7.3MHz, controlled by a rotary encoder with a variable step(10-1000Hz). The Arduino also controls TX/RX switching with the key input, and an OLED display for the frequency readout. The code for this can be found here:

The Arduino and Si5351 attached to what will be the main board for the radio

Having decided to get the receiver(direct conversion) working first, the next step was to build a mixer. I decided on a double-balanced diode ring mixer because it would provide a good level of sensitivity while also being easy to make myself. I used BAT41 diodes and FT-37-43 cores for the transformers, with 14 windings per side(or 7+7 for the tapped ones). I don’t know much about mixers, so I had to do extensive testing to get it to work. Using one of the other clock outputs on the Si5351 and an oscilloscope, I was able to get the proper output from it. I determined that I would need some filtering on it before the AF amplification stage. A 0.1uF capacitor across the output seemed to eliminate the high frequencies. It’d probably be best to make it a real low-pass filter with a choke on the line as well, though.

The mixer with both inputs and the output connected

Next, I started working on the AF amplification section. This is pretty simple, and I chose an LM386 for it. The next update will contain more information on this, as it is still in progress

After completing the AF stage, I will work on a bandpass filter, and then a TX amplifier, and TX/RX switching. I’d also like to add a built-in iambic keyer using an ATTiny.

Operating as K1RKX/W1 with my new CW QRP kit

I’ve been interested in getting into QRP portable operating. Recently I took a trip to Lake Champlain to do a bike ride, and decided I wanted to bring a radio. I decided on the 4 State QRP Group Hilltopper 20. It’s a 5w 20m only cw transceiver kit. It comes with 2 pre soldered SMD components and the rest are through hole, so it was an easy build. It took about 3 hours total. It’s controlled by an ATMEGA328 and an si5351 for the oscillator. It has a built in keyer for paddles, and will automatically detect what kind of key you have. It is very portable as well, weighing 8 oz and drawing 64ma on rx, 700ma on tx(at 12v).  I was able to power it off of 9 AA batteries or my 12v 12Ah SLA battery.

The radio is very easy to operate, having 4 controls. Gain, speed, function button, and tuning. The function button simply sounds the frequency in morse code, as the radio has no display.

I’d recommend this radio to anyone looking to build a simple kit or looking for a basic single band cw portable rig.

I was operating from the shore at the tip of Alburgh, right on the lake. The antenna was a resonant dipole, a few feet above the edge of a ~30ft or so “cliff”.  Apparently this was not high enough. I made a grand total of zero contacts, and saw no spots on the reverse beacon network. The only way I know it was working is that K1LOL in Swanton VT heard me at about s3(not bad for 5w ground wave at 10 miles really). I think next time I will set up a wire vertical, since that uses only one tree anyway. (I did end up bringing a tuner to check swr and power, and the radio and antenna were fine)

Operating from the shore of Lake Champlain, photo appears to be taken with a Baofeng

Field Day 2018

So with my new antenna up and my WAS count at 49, I thought I’d try to do field day a bit. My goal was to get 100 qsos under my own call, work Hawaii, and also operate a bit with a club. I did the third thing.

As K1RKX(1D), I made 24 qsos, all ssb, but I could have done much more had I actually spent time operating. I did not even hear Hawaii on any bands. This is strange, because I appear to have a blank spot on my spots anywhere north of VK/ZL and west of CA, but still can hear Alaska. I used the Kenwood TS-530s and doublet, I still don’t have a portable HF rig yet.

I did go and operate at the Fair Lawn Amateur Radio Club(W2NPT, 4A) for a few hours. I made around 30-40 ssb qsos on the 15M band.

I did however get a chance to use many different radios: an IC-706mkiig, an FT-847, an IC-7300, and a Flex 6500. The IC-706mkiig has a good receiver and is much smaller and lighter than I expected, but has very few controls and is very confusing. The FT-847 is a nice radio with a great receiver and an intuitive interface, but had some problems running on batteries/solar. I only had a couple of minutes on the IC-7300, but the IF DSP is great, and so is the touchscreen interface. The Flex, predictably, is the best of the four. Being an SDR, it needs a computer and is therefore not great as a portable radio, so it was running on a generator. The receive quality is very good, and can be even better if you play around more with the software. I could hear weak signals much better on the same bands with it compared to the other three.

Next year I plan to operate for 24 hrs straight, and portable, maybe even on solar.  I’d like to have an FT-817 by then or some other portable rig.

A new VFO for an old Kenwood

So I have a Kenwood TS-530s and I love it, but there are a few things I dont like. One of the problems is the VFO. It is old and analog and drifts as it warms up. This can be a bit of a problem for digital modes. So what I decided to do is take it out, and replace it with a DDS. This is easier than it looks, because all you need to do is remove 4 screws, unplug the connector, and move the lights out of the way if intend to move it more than a few inches(LEDs here because I replaced them). Then you simply slide the whole thing out, like so:

The VFO frequency needs to be from 5.5-6.0MHz, so I am using an AD9833 and an Arduino nano. I took the code from and modified it, so this is not 100% my code. The connections for the arduino are in this image:

Credit to

I simply removed all the code for the TFT and STEP encoder / waveform selector, as mine will not use these. The code is still a work in progress so I will not post it here yet, but I will update when this project is done.

So the first step is to see what the current VFO does. Here is a screenshot from the service manual which can be found at

From the service manual

The 5 pin connector on the back, with an oscope probe stuck in it

There is a 5 pin connector on the back of the VFO. The connections are:

RLC – This is the CW offset pin. When the radio is in TUNE mode or transmit in CW mode, I measured +8.23V on this pin. This biases a varactor diode to increase the frequency by 800Hz.

RIT – This is the RIT/XIT pin. When RIT was off, I measured 6.59V on this pin. With RIT on and full positive, there is 8.23V on this pin. Full negative RIT gave me 5.11V.

VFB – This is the 9V supply connector, but I assume this is also 8.23V in mine.


VFO – This is the VFO output pin. The output is a sine wave, 5.5-6.0MHz, and 0.2V PTP.

So now that I have this information, what do I do with it? Well so far my code makes the DDS output a sine wave from 5.5-6.0MHz, but it doesnt do much else. For RIT, I plan on using just a voltage divider and one of the Arduino’s analog pins as an input. The voltage divider is necessary because the analog pins only read up to 5V. RLC is easy. If there is voltage on that pin, the frequency is increased by 800Hz. I will probably power it from the same 9V, err, 8.23V line, but if this doesnt work I can look around the service manual for another power source.

Things I still need to do:

  • Figure out how to make the frequency increase faster as I turn the rotary encoder more
  • Make the output of the DDS cleaner and closer to 0.2V PTP
  • Make RIT work
  • Possibly add a non-volatile memory chip so I can have it remember settings when it gets turned off(or update the freq every time it changes?) I cant use the built in memory for this because it has a limited number of read/write operations before it fails.

I also have a Kenwood TS-700A 2M all mode rig that I would like to do this with, but the VFO does not appear to be anywhere near as easy to access. This can be a future project.

I will post an update on this once I get more things figured out. It’s mostly just code now.

A 140 Watt 2 Meter Amplifier

So I recently bought an untested KLM 10-140BL amp at a hamfest, for $20. I finally got around to testing it today. It’s a 140w linear amp for the 2 meter amateur band, 144-148MHz. It does not have a preamp. It will take 10 watts of drive power and output 140 watts.

KLM Electronics 10-140BL  

The front has just the IN/OUT switch to manually switch the amp in and out, and a lamp to indicate it is operating. It also has a pin on the back for automatic TX switching. It appears that even with the operate switch on, it is still in bypass until there is RF in it. When I transmit, I hear a relay click in the amp, the light comes on, and it outputs power.

The back of the amp

The back has only the antenna ports and the power / PTT connector. It’s a 4 pin Cinch-Jones connector. The top two pins are for the 12v power supply. The bottom left pin is PTT, and the bottom right is GND.


Back of the amp with cables plugged in

I tested this amp with a Kenwood TS-700a, and MFJ 300w dummy load, and an MFJ-945E tuner, for measuring the output. It’s an HF meter so it will not give an accurate reading, but its enough to see if there is any power output.

I did not have the correct power cable, so I had to improvise. I used a T connector from a VHF radio and another flat connector which may or may not have a name.

The radio used for testing

I plugged everything in, put the radio in CW, hit TX, and nothing happened. Then I realized I am stupid and I had one of the radio’s memory channels selected, not the vfo. I fixed that, hit transmit, the light on the amp came on and I heard a relay click.

The TX/RX switching works!

And heres what the power meter looks like:

It works!

It is amplifying! I don’t know if I am getting 140w, but it is definitely more than with no amp! I’ll have to get a power meter and measure the actual output. Note: the SWR is not actually infinite, thats just the meter. It may be slightly higher than 1:1 but since this dummy load is rated to 650MHz it should be good enough.

I now have an excuse to get a big yagi.

My HF antenna

I thought I’d start off by doing a post about my HF antenna. Right now I have a doublet of unmeasured length, estimated to be about 55 feet long and 45-55 feet high. I had a lot of help from Thomas W2XG, who also gave me the wire for it, so thanks!

All it is is two pieces of 12AWG wire of equal length, with some 300 ohm tv twinlead in the middle, and ropes on the end. The ropes are 1/8″ dacron designed for antennas, and are connected at the other end to some trees. The ladder line is probably about 20 to 25ft long and goes down to a balun made by K8EC. The balun has SO-239 connectors, so I have a piece of coax and some ring terminals to connect it to the twinlead. This is temporary, obviously. It will be fixed whenever I remember to and get myself to go look for binding posts. The other end of the balun is connected to some Belden 7733A coax. It’s very low loss, but also thick and has a solid 10AWG center conductor, which makes it very stiff. That is connected to the back of my MFJ-945E tuner, then a 3ft RG-8x jumper connects this to the transceiver.

I have been able to tune it no problem on all bands 80 to 10 meters, excluding 60m because my radio does not have that band. I can get out to western Europe on 80m, but not much farther. 40m performs very well, and I’m getting out all over the world. 20 is even better, I can get all the way to VK6, pretty much my exact antipode, no problem(FT8 at least). I am running only 100w into it.

So far it’s withstood maybe 30mph winds, but we havent had much more than that here since I put it up.

Here it is as seen from the roof, picture is taken with a baofeng: