Welcome
Welcome to my website. This site describes some equipment and circuits that I've designed and built. Many are related to amateur radio, but there are also some test equipment projects, kit builds, and other things that I have designed. I'd like to claim it's all been done to a plan, but that's not really the case. Development of this material tends to follow a fairly random process around here.
What's New?
I
designed several compact QRP antenna tuners (ATUs) for use with
portable HF QRP transceivers detailed here on my website. I described
one of these ATUs in more detail in an article that was published in
the January 2026 issue of Practical Wireless magazine.I have prepared a short background description in the design of these ATUs that you can find here. The various files for constructing the ATU can also be found at the end of this webpage.
I've completed
the conversion of the crystal controlled Mountain Radio Service MRS-1
portable HF SSB transceiver to VFO operation on the 80m and 40m HF
amateur radio bands. You can read about that and all the detailed instructions for the conversion here.This modification uses my new “SC+M” Si5351a-based SugarCube-Plus VFO. It's very easy to build because it uses thru-hole components, well, apart from the Si5351a SMD chip that lies at it's heart. You can read about the SC+M here.
We're planning to convert a number of these radios at our radio club. To help, I've also designed some test and calibration tools which you can read about here too.
Responding to a number of requests, I've upgraded the software for my very popular multi-tone CTCSS encoder . This change allows the user to save the CTCSS tone that is generated whenever the encoder is turned on.All of the other features are retained. The encoder can generate any of the 50 (!!) industry-standard CTCSS. The output is a very precise, stable and low distortion sinewave. It uses a standard rotary encoder, and the selected tone is shown on the tiny OLED display. All of the details may be found here.
I've designed a two-tone audio oscillator upgrade for my "DITA" precise 1kHz audio oscillator. This allows this ultra-simple audio oscillator to also generate a two-tone audio pair for testing SSB transmitters.
Two jumpers allow selection of either the original precise 1kHz DDS-generated audio tone or any one of three three sets of two-tone audio pairs.
Practical Wireless published my design in their February 2025 issue.
You can download the software and the PCB files from here.
Practical Wireless magazine published my tiny digital tuning aid ("DiTA") in their July 2024 issue. It's a highly accurate 1kHz DDS sinewave audio oscillator with a built-in speaker. An alternate 400Hz sinewave tone is available, too. This was designed to provide a precise 1kHz oscillator for over-the-air transmitter frequency checks. However, there are many other applications for it.
You can download the software and/or the PCB files and/or the industry-standard STL files to make the 3D-printed enclosure here.
Here are the details on the modification of the legacy AWA TR-105 portable 5W PEP HF SSB transceiver.
Withdrawn from search and rescue service some years ago, this allows it to be used on the 80m and 40m amateur radio bands. The modifications are much easier to complete than for the tiny Condor (below).It's possible to create a kit for this if there is sufficient interest (Email me!). It won't be very expensive. All of the parts required are easy to find and quite inexpensive.
This series of web-pages describe the tiny Condor 2 channel handheld Search and Rescue 1W HF QRP SSB transceiver and the modifications required to convert it for ham use on the 80m and 40m HF bands. Designed and made in New Zealand, the 2-channel Condor entered service during the 80's. It's a novel design using the phasing SSB method(!!) Some of the original Condors are still being used.The first part of this series introduces this transceiver. Next, Part 2 describes the special version of my SugarCube-Plus VFO for the Condor. The detailed description of the modifications required to convert the Condor for amateur radio use on 80m and 40m is here in Part 3 Condor Conversion. I'll also describe a compact antenna tuning unit (ATU) and SWR bridge shortly (The Condor is designed for 75 ohms!) as well as some alignment and testing accessories.
The Condor replaced the much larger TR-105 SAR transceiver, an HF radio I've previously described here.
Here are some details on the legacy AWA TR-105 portable 5W HF SSB transceiver. The (much) older TR-3 AM transceiver is often mistaken on the internet for the TR-105 because they are both yellow. Any day, I expect to see a photo of a giraffe in yellow pyjamas incorrectly identified as a TR-105!
Many years ago, I was supported the maintenance and operation of about 150 Search and Rescue TR-105 radios. TR-105 radios were also used by Mountain Radio Service in New Zealand for many years. You can read about the TR-105 here.
I've finally completed the 99 channel
version of my set of fixed-frequency SugarCube+ oscillators. Any
channel can be programmed from 5kHz to 290MHz. And it's super-compact,
of course, and incredibly easy to build.The 64x32 or 70x40 pixel OLED shows the channel selected with the rotary encoder. You can also define the "start" (wake-up) and "last" channel which your SC+99 uses.
Frequencies are user-programmable via a spreadsheet. A mouse click generates the EEP file for uploading to the SC+99's EEPROM. The details are all here.
My
local amateur radio club decided to build SugarCube+ VFOs as a club
project. I was asked to help arrange the initial run of ten kits. It
ended up being quite a journey. That seems to be the rule with kit
production.It all turned out successfully, I think, and you can find the information here including the detailed kit-building instructions. You can get details of a new PCB I designed to hold all the front panel parts as well as a 3.3V regulator.
I've also added links on this new page to all the other SugarCube pages on my site.
I was asked if one of my CTCSS encoders could replace an obsolete CTCSS
encoder chip that was used in a legacy ham transceiver. These devices, primarily made by CML, MX-Com, Panasonic and Seiko, were often used by Kenwood, Yaesu, Icom and Trio in their FM transceivers. Some can be very hard to find now.After some detailed study, I've designed and tested a further version of one of my CTCSS encoders. This encoder allows you to select one of four different tone schemes in the software. This allow this design to replace the encoder functionality of some of these increasingly rare and often expensive CTCSS chips. You can find the details here.
CTCSS is
widely used in ham radio, just as its been for many
decades in professional two-way radio systems. Having
looked for a
suitably small and cheap CTCSS encoder to help restore several old VHF
transceivers around here, I ended up designing three different high
performance CTCSS encoders. They all share the same tiny single-sided
PCB.You can read more about two of these CTCSS encoders here...
NEW: FIVE different CTCSS tone sets are now available to you to download.
Here's a new easy to build multiband modular Si5351a VFO with keypad and rotary encoder tuning. It's a design for those who look at my SugarCube VFO designs and say “I couldn’t ever build something that small!” This design uses a few low-cost modules to make construction easy. I've also created an Excel spreadsheet to allow you to enter the band edge frequencies for each of the nine bands (or memories) supported by the VFO, as well as the start-up frequency for each band. You can precisely set the reference crystal frequency, too.
It's all described in detail here...
If you need an RF oscillator for your transceiver for a few fixed frequencies, or an alternative to expensive crystals for a radio restoration, or maybe you want a multi-channel RF oscillator with lots of fixed frequencies, then one of the three new versions of my SugarCube-Plus may be exactly what you need. The 20 x 20mm SC+4 and SC+16 deliver up to four and sixteen fixed programmable RF frequencies anywhere from 5kHz to 290MHz! There's an optional OLED channel display, too. The channel digits can be easily seen from across the room.
You can enter your frequencies using my new spreadsheet. It can save the data to EEPROM in Atmel's EEP format on your hard drive, too. The details are here.
A
number of my designs use all of the pins on the microcontroller. If you
have to reprogram those ATtiny chips, you must first reset the chip
fuses. If you build my new channel-based SugarCube-Plus, you'll need
one of these. It resets the fuses in any 8-pin ATtiny85 back to
factory-default condition.Using widely available parts and running from a USB port or wall wart, it's a very low cost solution when you need to reset ATtiny chip fuses. It also clears the flash and EEPROM memory to allow the Lock fuses to be reset, too. It works on tiny13, tiny25 and tiny45 devices as well. Details can be found here.
When
I designed several compact CTCSS encoders in early 2020, I
thought that would be the end of it. But requests for details of my
multitone CTCSS encoder I mentioned briefly in the text have just kept on coming ever since.
I just quickly tried that extra software in passing while designing the simple encoders.Well, I've now documented two versions of my multitone CTCSS encoder. The first uses the same tiny PCB as the basic CTCSS encoders, while the second version features a slightly larger PCB, an improved filter, and a portable battery powered enclosure. Both feature an OLED display. You can find all of the details here.
Designing a reliable compact cost-effective fully-featured software-based CTCSS decoder
that actually works over a wide range of audio levels and in the presence of noise is a serious technical challenge. CTCSS decoders used to be widely available at modest cost. Now, they are hard to find (and expensive!) with CTCSS integrated into almost every new transceiver and handheld.
So is a combined CTCSS decoder/encoder ('dencoder') modulae of any use to anyone these days? Here's a background to designing CTCSS decoders and some possible applications and solutions...
Silicon Chip magazine published two more of my designs in their September 2020 issue. Both are illustrated on the cover. The first design is a blinking night-light 'lighthouse', an ideal project for those starting out in the electronics hobby or a grandparent looking for an inexpensive project to build with grandchildren.
The second of my designs is a compact 'shirt pocket' sized battery powered digital audio oscillator using an 8-pin ATtiny85. The design features a standard rotary encoder which uses just one I/Opin on the ATtiny85.
All of the details are available from the Silicon Chip website.
Practical Electronics magazine in UK published one of my designs in their June and July 2020 issues - An AM/FM/CW HF and VHF scanning signal generator.
Previously published in Silicon Chip magazine in 2019, it covers from 100kHz - 50MHz and 70MHz-120MHz, or 150 MHz with reduced output.. Some information is described here on this page about solutions to a couple of problems experienced by some builders.
Some of our extended family stayedg with us during the COVID-19 lockdown here in New Zealand. Our eldest grandson needed a
light for bedtime reading to avoid waking up his younger brother. I had an old NiteOwlTM gathering dust at the back of a shelf. Some basic design issues led to its rejection a decade earlier. But where there's a need, there's a way!
I converted this old near-useless incandescent reading torch into a highly efficient LED torch. You can read more about it here...
If
you are REALLY squeezed for space in your design, here's the latest
addition to the Sugarcube VFO family. Following a request for an even
smaller display, I've now added a version for the tiny 0.49" 64x32
pixel OLED displays. All of the features, including user-programmable
settings, are retained. The dual-band capable SugarCube software all still runs inside the 8k memory of the little 8-pin Atmel ATtiny85. All of the details of this version can be found here...
I've just developed new software
for the SugarCube VFO, a Si5351a based VFO with dual VFOs and
quadrature outputs. Not only have I added dual BFOs and improved
tuning, but thanks to a suggestion from Eric, ZL2BMI, I've added user parameter programming. And all of this still fits (just!) inside the 8k memory of the little 8-pin Atmel ATtiny85. Cheap, easy to build and use. The details about the updated software for the SugarCube VFO is here....
This handheld compact portable 3-output HF/VHF Si5351a RF test oscillator started out as a basic Si5351a software test platform but it quickly grew as features were added. The choice of
keypad and tuning knob make it easy to use. Powered by a single 18650 Li-ion cell and recharged from a standard USB charger, its low power consumption allows it to operate for several months of intermittent use before needing recharging. It weighs just 170 grams (6 ounces).
It doesn't have an attenuator or the modulation features on my all-mode Silicon Chip RF signal generator (See below). However, it can generate AM modulation!
You can read about it here....
I've developed what I think is the smallest Si5351a VFO complete with a fully functional OLED display. My SugarCube VFO measures just 20 x 20 x 12mm
excluding the modest 23mm (0.91") OLED graphic display, encoder and
pushbuttons. It features dual VFOs with quadrature outputs, plus a
BFO/CIO output, operation to nearly 300MHz, and a neat bright clear
frequency display to 1Hz. I describe a VHF FM receiver application, too.Parts cost? Less than $US10. You'll find all the details about my little SugarCube VFO here....
Popular Pages:
My compact digital SWR meter
for QRP (low power) transceivers and transmitters weighs in at just 50
grams. It's powered from a single AAA battery and uses a bright, easy
to read,
OLED graphics display.Some new 0.96" OLED displays didn't work correctly with the original software. Bob ZS6RZ brought this to my attention helped test the revised software. Thanks, Bob!
ATtiny45 and ATtiny85 versions are available as well as the larger 1.3" OLED displays with their (similar, but different) SH1106 controllers.
I
finally got some time to build my MKARS-80 80m SSB kit transceiver which I purchased some years
ago. It used a PIC as a frequency counter to control the analog
VFO using the 'huff and puff' method.Naturally, I decided to upgrade it with a new version of my single band si5351a VFO/BFO. This version uses a cheap Arduino Nano along with the kit's standard 16x2 LCD. My design features selectable tuning steps, an S-meter and RIT. (More features might be added later...) It's also still in the rough prototype stage but the details of the new design are here...
This photo shows an electrically heated towel rail. I've designed an AC delay timer for mine. It saves power and avoids the need to nag my family members about turning it off every morning. I know - A 'First World' problem.
It is a solution which may have other applications where switching AC loads is required. It uses one of the 8-pin Atmel processors, The details can be found here...
My si5351 dual output VFO/BFO has more features than I can list here, and remains very popular. Over 3,000 downloads of the software now! It
uses a Nokia 5110/3310 graphics LCD and
it covers all of the usual amateur radio bands.
Add more if you wish. The VFO's low power consumption (Just 30mA at
3.3V) makes it suitable for QRP, and it's cheap to build. The details are here... Kits have been supplied by others via the Internet (without crediting me in any way for the hardware design or the software). That's why it may look familiar to some.
And thanks to Cristi YO3FLR, there's a PCB layout available in the Download section on my VFO's webpage.
My single band si5351 dual output VFO/BFO also remains popular. It uses fewer than 20 parts including an 8-pin ATtiny85 and an
I2C alphanumeric LCD display. An S-meter/RF power meter display is
built-in too.
Same low power consumption.There's also an updated PCB layout available, too.
The details are here...
Wait...There's More! - How to Navigate the ZL2PD Website
You'll find the complete list of my published designs down the left hand side of this page. Just click on any item to take you to that design. Schematics
and other drawings are to be found all over the site, as are photos.
Want to see the details close-up? Then just "right-click" on the image
or schematic or whatever with your mouse. Chances are, you'll now be able to see that stuff in much
more detail. And you can download many items too, if you wish. Is something not there? Just email me and ask. Some material is not immediately available because of rampant copying and subsequent sales of downloaded material from my website over the past few years by some individuals and companies. All without permission or reference back to me. If customers later had questions, most just told their customers to email me!
To date, the details and designs here on my website include:
- Several transceivers (For some reason, these have been mostly other people's designs! Must address that soon...)
- Accessories for these transceivers (DDS VFOs, ATUs, SWR meters, etc )
- (Lots of) Oscillators and test equipment
- Switchmode power supplies
- A temperature-controlled soldering iron, and
- Some family-related designs (An unusual LED clock, an electronic sand-dial timer, a binary thermomenter, a Christmas tree...)
Elsewhere on the ZL2PD website ...
A suite of three different designs for temperature controlled soldering stations,
with a detailed design for the most compact unit. It uses a single
8-pin ATtiny25 microcontroller and not much else, and it is packaged in
a compact 3D-printed enclosure, also of my own design.(Right-click the image for a closer look or visit my web page)
For those looking for something a little different, here is a Four Dot Clock which uses just four cheap LEDs (Four dots of light, if you will) to display the time. It's surprisingly
accurate. I only adjust it now about once every six months.More interestingly, perhaps, is the fact that, unlike most clock designs you might have seen, this one does not require another chip to actually do the timekeeping. The clock's ATtiny45 does all that, and more.
Here are the details of an earlier design for a compact digital RF signal generator
using a Cirrus Logic CS2000 chip. It's compact, with everything inside
a small 3D-printed case. It generates a 3.3V squarewave output from 1.5
to 160MHz (although the specs on that chip claim it is limited to
75MHz) and draws less than 20mA from a 4 - 15V DC supply. It's really the result of a tale of woe and misfortune, but the circuit works... More details here.
Of course, all of the other designs are still available to browse and build, each listed over to the left in the index. Help yourself!
New Designs... Well...
A really compact LC meter (Actually, I've designed three or four of these so far...)
Stay tuned...
The Legal Stuff
You use the information published on these web pages at your own risk!
You
may use the information
provided here for personal or educational purposes but you may not
reproduce it in any form or use this information for any commercial
purpose without
first obtaining written permission from the copyright holder.
There is no warranty or guarantee, either expressed or implied,
covering any information of any kind which may be available from this
website or any correspondence associated with this information,
or that designs and information provided on this website are
free from patent or intellectual property rights of the author or third
parties.
Should the information contained on this website be used by any party,
that party shall by using the information provided be deemed to take
complete responsibility for all risks and liabilities associated with its use and hold the
author of this website harmless in the event of any claim, loss,
liability or expense associated with any such use.
The rights of copyright over the contents of this website, unless
otherwise noted, are claimed by Andrew Woodfield ZL2PD.
