This is the original version of the direct conversion receiver block. I used it in the Two Band SOTA Transceiver.

The direct conversion receiver block takes the antenna input (J1) from the transmit board’s LPF and outputs audio I/Q for feeding to the audio phasing and amplifier board. It includes a pre-amp but I eventually disabled this as I found it often overloaded. There is plenty of gain so I have never missed it. On higher bands than 20m it might be useful.

Based on the 5 band transceiver.

My original motivation for home brewing a transceiver was for SOTA activations. I’d been using an FT817ND very successfully but found it awkward to use with an external CW filter and battery plus the Yaesu’s form factor isn’t all that convenient when sat on a hilltop. I had built a 30m QCX kit so knew it was possible to build a high performance CW rig. This finally led to my 5 band transceiver but that’s a base station so I needed a portable version. For SOTA 40m and 20m give good European coverage plus the chance for some DX. I decided to simplify the user interface and do without an LCD screen. I had a tin that was a “Gift in a tin” sewing kit that one of my daughter’s had finished with. I realised I could just about fit 4 of my transceiver PCBs in so all I had to do was produce a two band transmit board and a SOTA in a tin transceiver was possible.

The 5 band transceiver is fairly easy to use although there are a few oddities. These are because I originally only had one pushbutton as part of the rotary encoder but have since added two more buttons to make it easier to use. Each button has a short press and a long press. Usually a short press enters a setting and a long press exits it. I hope to eradicate the quirks and make the interface a bit more logical in due course. In writing this I have noticed one or two bugs that I shall fix in due course. I shall probably make other changes too.

Part of the 5 band transceiver.

The final board for the transceiver is the transmit board. Actually there are 5 boards, one per band. You can, of course, build fewer boards for whichever bands interest you. The limitation of 5 is due to the number of I/O lines that are available on the the microcontroller. More could be supported by using an external I/O chip or decoder. This would require software changes, although they would be straightforward.

Part of the 5 band transceiver.

The phasing audio filter and amplifier board is the final board required to build the receiver. It takes the in-phase (I) and quadrature (Q) audio from the direct conversion receiver block and applies a 90 degree phase shift to cancel the image, sends it through a 200Hz CW filter and amplifies it for headphones.

Part of the 5 band transceiver.

The direct conversion receiver block takes the antenna input (J1) from a transmit board’s LPF and outputs audio I/Q for feeding to the audio phasing and amplifier board. It includes a front end switch to isolate the receiver during transmit, switchable attenuator and pre-amp, and a splitter to feed a signal to an external receiver.

Part of the 5 band transceiver.

The clock and control board is the heart of the transceiver containing the ATtiny 3216 microcontroller and Si5351A clock generator chip. It generates quadrature clocks for the Tayloe detector in the receiver and the transmit clock for the class E PAs. It also controls the display, morse keyer, transmit/receive switching and so on.

I’ve been using my 40m/30m/20m end fed half wave antenna very successfully on SOTA activations but it requires a reasonable amount of space. I thought it would be interesting to try a vertical so that on busy summits (or in other portable locations) I could just bungee my 6m fishing pole to a fence post and get quickly on the air. To avoid needing long radials I still wanted it to be a half wave. The only trouble is, a half-wave on 20m is 10m and my pole is only 6m long!

With many of the tinyAVR family only having 8K of flash space it is sometimes necessary to squeeze your code really tightly to make it fit. Here are some tips on how to do this.

I’ve been using AVR microcontrollers for a few of my projects. The ATtiny85 is a great little 8-pin DIP or SOIC chip which is perfect for a morse keyer or controlling an LCD display over I2C. For those projects requiring more program space I’ve used the ATmega328P in the form of an Arduino Nano, but this is quite large and the only surface mount part is in a package I’m not confident I can make a PCB for or solder. The ATtinies are limited to 8K program space which is just not enough.

In many of my projects I use the ubiquitous 16x2 LCD display. These are available for a few pounds from eBay and other suppliers. They are widely used in Arduino and other hobby projects and so information on how to use them, along with software, is widely available.

I have various projects using AVR processors (ATTiny and ATMega) so there is a lot of similarity between the various source files. Rather than keep multiple copies of the same code I have created TARL - the TGJ AVR Radio Library. This is a set of source files for AVR processors that provide functionality of use in amateur radio applications, although many of the files could also be used in non-radio systems.

There are lots of ways to prototype with through hole components - dead bug, Manhattan, Veroboard etc. But it is much harder with surface mount. I have used adapter boards with SMD ICs and have used a tile scribe to cut tracks on copper clad board but this is not practical with ICs or for circuits of any size. So I have started making my own PCBs.

I’ve been playing about with simple transmitters and receivers. The former are easy - a crystal oscillator, PA and key shaping circuit. But receivers are much harder so I’ve been using my existing Arduino based direct conversion receiver. This means I need a way to switch the antenna between RX and TX so I’ve built an RF sensing changeover circuit.

Amber beer is more of an American style (and Irish Red Ale is similar) but it has many similarities with British Bitter. I called this amber as it is darker and less bitter than the beers I normally brew. It’s the first recipe I’ve put here as I was delighted with how nice it is, especially when served through a traditional beer engine. Although I’ve called it British it is a mixture of British and Canadian malt and British and American hops. The yeast is distinctly British though (although via Oregon!).

I have updated the software to v1.1 for the keyer so that the keyer mode and the slow and fast speeds can be set by programming the EEPROM with a simple text file. This is easily done with avrdudess or other tool. This means there is now only a single hex file instead of different versions for each keyer type. You can change these settings without having to rebuild the software - you don’t even need to install Atmel Studio if all you want to do is make the keyer and set your favourite mode and speed.

Update 10/4/2020: I have released v1.1 of the software to set the configuration from EEPROM. See this update.

My direct conversion transceiver works very well on 40m but when I converted it to work on 20m I found that it suffered from an annoying hum. This is a very common problem with direct conversion receivers due to local oscillator leakage and is more likely on the higher bands. The usual cure is to add filtering to the power supply. As the hum was still there when powered by a battery this was not a solution for me.

I’ve replaced the 40m Class E PA in my QRP transceiver with a class D amp so that it will work on more than one band (with suitable LPF of course). I had my first two ever 60m CQ QSOs with it at the weekend. I have a key shaping circuit using the same values as in the class E amp but the key up and down transitions were too fast so I changed the component values to increase the delay. I was surprised by the resulting waveform for key down:

My 40m homebrew transceiver is controlled by an Arduino Nano clone. The tuning knob is a rotary encoder which has three pins - ground, A and B. A and B are connected to digital inputs with an internal pull-up resistor, so when the pin goes active a logical zero is read. Rotating the control produces two square waves in quadrature. For example, a series of counter-clockwise clicks produces the following:

This is the audio switch I am using to mute the receiver when transmitting. When switching to transmit we need to mute the receiver quickly but we want the switch back to receive to be slower. This is to avoid clicks and thumps.

I’ve now tried the 20m dipole on a couple of SOTA activations. So how does it compare to the EFHW? It works, but I felt it didn’t offer any benefit over the EFHW. Of course, this is not a fair comparison. I didn’t use the antennas side-by-side so location and propagation would have had a huge influence on my observations. I just didn’t feel like I was getting as many QSOs as I do with the EFHW. There are also some practical advantages in favour of the EFHW. I should also point out that, since the EFHW works on 40m, it is twice as long as the dipole.

I have written ABVCalc which is a little Android program to calculate the ABV (Alcohol by Volume) of beer from the original and final gravities. You can enter gravities as, for example, 1044, 1.044 or 44. It also calculates the apparent attenuation.

I have had a lot of success with my EFHW antennas for SOTA activations but discussion on the RSGB Technical Forum made me wonder if the matching transformer was too lossy. If it is open- or short-circuited you would hope for an infinite SWR, although in practice 10:1 would be good. I was getting around 2.5:1 when open and 6 or more when shorted. So it appears to be lossy, although it clearly works and is easy to deploy. It is inherently multiband too (a half-wave for 40m is a full-wave for 20m, for example).

This is based on an article published in Sprat 177 (Winter 2018/19). There is also an update at the end.

I used to really hate wiring up coax connectors. I’d decide I needed to wire up a lead for some purpose and order the plugs. They’d arrive and then get put in a box somewhere never to see any cable. Soldering PL259 UHF plugs never seems to work. Although the centre pin is easy to solder, if you don’t file it down it then sticks in the socket and forcing it apart breaks something. Then trying to solder the braid seems impossible. If you manage to apply enough heat to the plug’s body to get a decent joint, it melts the dielectric and you get a short between inner and braid.

Unfortunately there isn’t a single place to get all the tools and components you will need for home construction. These are the sites I have used and recommend:

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