Tag Archives: Digital Modes

From idea to kit: Adam introduces the Arduino Digital Modes HF QRP Transceiver (ADX-S) kit

Many thanks to Adam (BD6CR) who shares the following guest post about his latest project:

From Open Source Project ADX to Kit ADX-S

by Adam (BD6CR)


Original Design: WB2CBA

Modification and Kitting: BD6CR

I knew Barb, WB2CBA from his uSDX design a few years ago and I introduced both DL2MAN and his designs in my blog. So, when I came across the ADX – Arduino Digital Xcvr a few months ago, I immediately ordered both the ADX (through hole) and the ADX UNO (surface mount) PCB samples.

I started building the ADX UNO and put it in a dental floss case and made a few contacts on park bench. However, the soldering is too much for my eyesight. So, I turned back to the ADX because I don’t need to solder any SMD parts, since both the M328P and SI5351 are module based. I could build the project in 3 hours and it worked the first time.

However, I felt unsatisfied with the strong BCI since the CD2003 radio receiver chip was connected as a direct conversion receiver. JE1RAV mentioned in his QP-7C modification project that he tried JA9TTT’s idea to build a superhet SSB receiver with the TA2003 or CD2003, so I tried and it worked very well. I have decided to name the new circuit as ADX-S, where S stands for Superhet.

I shared the great news with Barb and he encouraged me to carry the flag to make it a kit, since my design D4D was his first digital radio and he loved it.

You can refer to Barb’s page on ADX here.

My hardware modification can be outlined in this schematic. I have added an FL1, PFB455JR ceramic filter by Murata and a C25 coupling capacitor from CLK2 of SI5351 module. The RX audio comes from pin 11 instead of pin 4.

I modified it by cutting two traces on the ADX PCB and it looked ugly, so I redrew the PCB. Continue reading From idea to kit: Adam introduces the Arduino Digital Modes HF QRP Transceiver (ADX-S) kit

Guest Post: A QRP Labs QDX POTA Field Portable Report

(Photo: QRP Labs)

Many thanks to Conrad (N2YCH) who shares the following field report:

QRP-Labs QDX Field Report

K-1716, Silver Sands State Park, Milford, Connecticut

January 13, 2023

By: Conrad Trautmann, N2YCH

A digital mode multiband transceiver for $69? Yes! QRP Labs has the QDX kit available for $69 US. Add $20 if you would like a very nice black anodized aluminum case to mount it in and if you want it assembled and tested add another $45. Visit the QRP Labs web site for all of the details (QDX 4-band 5W Digi transceiver (qrp-labs.com)

How well can a $69 digital transceiver work? Read on…

I ordered my QDX kit back in May 2022. It arrived in June, I assembled it and ran some tests at home. It worked well on FT8 into my home antennas. It interfaces nicely with WSJT-X and I liked the idea of using a low power transceiver to band hop on WSPR. My QDX is an early four band version, which does 20, 30, 40 & 80 meters. I set it to band hop on all four bands not remembering that my multiband offset center fed dipole is not resonant on 30 meters. Since the QDX does not have a tuner, it didn’t like the higher reflected power of a two minute long WSPR transmission into a bad load and smoke resulted. I was fortunate that the failure was isolated to the RF power amplifier transistors and replacing those got me running again. This was my own fault, not the transceiver. Now, it band hops on 20, 40 and 80 meters with no issues, I eliminated 30 meters from the hop schedule.

I share this important story at the beginning of my field report as a warning to anyone considering using a QDX to be very careful when connecting an antenna to it. Since the QDX does not have an internal antenna tuner, you either need a resonant antenna or must use an external tuner to provide a 50 ohm load with low SWR to the QDX. The QRP Labs groups.io site has a number of posts from users with different tuner suggestions.

Now comes the fun part. I visited Silver Sands State Park, K-1716, located on Long Island sound in Milford, CT on January 13, 2023 in the afternoon. While it was Friday the 13th, I had nothing but good luck. Knowing I would be running QRP power, I decided to use what I consider to be my best 20 meter antenna. It’s a modified version of a Buddipole, which I call my “no coil” Buddipole dipole. I use a Buddipole VersaTee mounted to a WILL-BURT Hurry Up mast, which is a push up mast that extends to about 25’ high. The dipole consists of two Buddipole 32” accessory arms, one for each side of the VersaTee and two MFJ 17’ telescoping whips, extended to just about 17.5’. This provides a very broad bandwidth and low SWR on 20 meters. See the screen shot of my antenna sweep from the RigExpert analyzer below.

Here’s a photo of the antenna in the air.

The temperature on this January day was a mild 55 degrees so I was able to set up my equipment in the back of my Jeep. Here’s everything I needed to do the activation. Since the antenna is resonant, I did not use a tuner.

My iPhone gives you an idea of just how big the QDX is, which is sitting just to the right of it. There are only three connections needed, the antenna cable, a 12V power cable and the USB cable. I was using my Bioenno 9ah battery for power. I brought the Bird Model 43 with a 25 watt element in it to monitor the output power and also to measure the reflected power, which barely even nudged the meter. It was effectively zero watts reflected. In the photo above, I was in a transmit cycle and you can see the power meter just a touch above 5 watts. On the computer, you can see a mini pile-up of six hunters in the queue. One thing to note about the QDX is that you can’t adjust the power by lowering the PWR slider in WSJT-X. It’s recommended to leave that at maximum. The way to adjust output power is to adjust the power supply voltage. In this case, the Bioenno had a full charge, so the radio was running full power.

I began the activation without spotting myself, just to see who’d hear me. Here’s a map of the pskreporter showing my spots.

I eventually spotted myself so hunters would know what park I was at. I was amazed that during my activation, I never ran dry or had to call CQ POTA, there was a steady stream of hunters the entire time. The QDX does a fine job receiving, here’s a screenshot of WSJT-X including the waterfall to show what it was receiving.

So, how did the $69 radio do? In a one hour and 17 minute activation, I completed 46 FT8 QSO’s. Here’s my coverage map.

I managed to complete three park to park QSO’s, too. One park called me and I called the other two who heard me and answered. I use JTAlert which helps me keep track of the order of who called. I always try to answer the hunters in the order they called me. I’ve set up a Directed CQ alert in JTAlert for anyone calling “CQ POTA” which helps me to see who else is at a park while I’m activating. If I’m able to contact them, I use the POTA spot list to include their park number in the SIG_INFO field of my log, which is N3FJP. N3FJP is handy to use since I start a new log for each activation and I’ve configured it to upload to LOTW and QRZ when I’m done for the day.

Another thing worth noting is that there is no speaker on the QDX. I’m one of those digital operators who actually listens to the cycles while I’m on the air. It provides a certain cadence to hear each cycle go by so you know what to be looking at or clicking on and when. With no sound coming out of the QDX, it forces you to find that cadence by looking at the computer screen. For me, it means watching the receive audio levels and the progress bar to see if I’m transmitting or receiving. The QDX does have a single red LED on the front panel that will flash during transmit cycles, which is also a helpful indicator.

I’d say the results shown here speak for themselves. I had a steady stream of hunters, I had just one or two QSO’s that needed a second RR73 to confirm and the coverage was as good as most activations I’ve done with more expensive radios and more power. Despite the self-inflicted hiccup I experienced at the beginning, I’d say that If you’re looking to try activating digital for Parks On The Air or even for your home, the QDX certainly works very well and provides a lot of value for the money.

Using WSPR Data to Study Propagation 40 & 20 Meter Bands

Many thanks to Jim (KX4TD) who writes:

Hi Thomas,

I am a subscriber and ham radio operator circa 1974. Like you (and a lotta hams) I started as a SWL using a transistorized Lafayette Radio receiver.

Last evening, I listened to the April 2022 Wireless Flirt podcast from Ireland where you were interviewed about the comeback of SW radio. Well done Thomas! You are one articulate dude!

I currently have a uBitx that I use for base and portable operation. We share an interest in POTA and other QRP field operations.

My latest obsession is WSPR. Attached [linked below], please find some of my WSPR findings on 40 meters.



Click here to download PDF: “Using WSPR Data to Study Propagation on the 40-meter and 20-meter Bands”

Thank you so much for sharing this and for the kind words, Jim! It’s strange, but I’ve yet to dive into the world of WSPR. I actually have a QRPLabs QCX+ transceiver kit I purchased specifically to explore WSPR. I just need to find the time to build it now! 

Thanks again for sharing your amazing report!

How to use the Reverse Beacon Network (RBN) for automatic POTA and SOTA spotting

If you’ve read my field reports or watched any of my activation videos, you’ve no doubt noticed that I rely very heavily on automatic spotting  via the Reverse Beacon Network (RBN) for both POTA (Parks On The Air) and SOTA (Summits On The Air).

I’ve gotten a lot of questions about how to use the RBN functionality for both SOTA and POTA, so thought I might clarify (in very basic terms) how the system works and how you can take advantage of it.

Note: CW and Digital Modes Only

Keep in mind that Reverse Beacon Network spotting only works with CW and some digital modes.

I, personally, have only used it for CW activations.

The system does not currently recognize voice transmissions (although as voice recognition becomes more accessible and effective, I wouldn’t be terribly surprised if something like this is offered in the near future!).

Here’s how the RBN works

The RBN is essentially fueled  by a global network of volunteer receiving and decoding stations that feed information into the RBN spotting system. This system is running 24/7 and recording spots constantly.

This is what the RBN spots search results look like using my call at time of posting.

If I hopped on the air right now and made at least two generic CQ calls with my callsign–barring any abnormal propagation–the RBN would no doubt collect my information and spot me automatically to their network.

Click here, for example, to see all of the times the RBN has spotted me recently. Click here to search for your own callsign on the RBN.

To my knowledge, the RBN is a completely independent resource and not directly affiliated with POTA, SOTA, WWFF, or any other contest or activity. Continue reading How to use the Reverse Beacon Network (RBN) for automatic POTA and SOTA spotting

FT8 Portable: Steve takes his Phaser Digital Mode Transceiver to the field!

Many thanks to Steve Allen (KZ4TN) who shares the following guest post:

FT8 QRP Portable

I recently finished my Phaser digital mode QRP transceiver kit and have had a hankerin’ to take it portable, and today was the day.

Temps were in the upper 60s with clear blue sky. About fifteen minutes from home is the Watauga Point Recreation Area on Watauga Lake in Carter County, Tennessee. It’s a day use area and is not an official POTA site, though it is in the Cherokee National Forest, which is. I opted to not make this a POTA activation as it was more of a first time “proof of concept” trip.

The Phaser is a small digital mode transceiver designed by Dave Benson, K1SWL with the enclosure the design of AA0ZZ, Craig Johnson. Phasers were available for most all of the HF bands, put out between 3 to 5 watts, and in addition to FT8, have the ability to program a second frequency to operation other digital modes such as PSK-31. They were sold and supported through Midnight Design Solutions, but unfortunately are no longer being offered. Occasionally I see them coming up for sale on the QRZ.com swapmeet forum.

In addition to the Phaser, I brought an FT-891, an LDG Z-11Pro 2 tuner, a netbook computer, and two batteries; a small AGM for the Phaser and a deep cycle lead acid power pack for the FT-891. I brought my W2LI magnetic loop antenna and a homebrew “NorCal Doublet” that sets up as an inverted V on a 20 ft kite pole as a backup antenna. The whole kit (excluding the batteries) fits in two wooden ammunition crates which make it really easy to drive, set up, and operate.

One note on using the W2LI mag loop. You need to first tune the antenna using the radio and listen for an increase in the background noise level. Using the Phaser while connected to my computer made that not possible. If I had brought a small set of earphones I could have plugged them into the audio out jack on the Phaser and tuned for max background noise. So, instead I connected FT-891 to the loop and used it to tune the antenna to 30 meters. Next time bring earphones.

After about fifteen minutes I had the station set up. The waterfall on WJST-X showed that the Phaser was receiving transmissions but no displayed text. Unfortunately I had neglected to synchronize the computer clock before I left the house. The netbook is pretty old and the internal battery needs to be replaced. What to do? First I tried to manually sync the clock to WWV but Windows 10 won’t let you set the seconds in the clock to 00. As I had cell service I figured I could use my cell phone as a hotspot. Never having set it up before I have to say that it was pretty easy. Thank you 21st century tech! This allowed me to sync the internal netbook clock, but it also let me log contacts on QRZ.com, and check my propagation on PSK Reporter.

The Phaser puts out around 3.5 watts, so I didn’t respond to a CQ that was less than -5 dB. While PSK Reporter showed reception of my signal up and down the East coast, contacts were scarce. I seemed to have a window open up into New England as I worked PA, MA, and CT. I was right in the middle of my fifth contact when the computer battery died so that was it. WSJT-X reported these stations on the +dB side for reception but my signal strength was always reported at < -10 dB.

The 30 Meter band was up and down with band conditions being reported as only Fair on the Solar-Terrestrial Data report on QRZ, and at one point for about a half hour there were no signals displayed on the waterfall.

With a loop antenna on a tripod and 3.5 watts I can’t complain. I’m thinking of building an RF amplifier to boost the output up to 10 watts which should help. My next step is to load WSJT-X on my tablet and see how portable of a kit I can assemble. As FT8 was designed as a weak signal mode, it’s perfect for QRP portable operating.

Steve Allen, KZ4TN

The HF Pager application

Many thanks to Pete (WB9FLW), who shares a link to this smartphone application-based digital mode called HF Pager:

(Source: NVIS Club)

Using Your Smartphone on Shortwave

A highly capable HF Data Mode for Android Phones

By Evgeny Slodkevich, UA3AHM/OH5HM, and Dieter Kuckelkorn, DL1DBY

When going to an outdoor camping trip, we will find that in many parts of the world there is no cell phone service avail able in the back country. To make matters worse, in these areas there is almost never a VHF/UHF ham radio repeater in range when we need wide-area coverage. Apart from strictly local communications using VHF/UHF simplex radio, how do we send messages to friends and family over great distances? How do we call for help? A similar problem can even arise in an urban environment if a major disaster strikes like the break-down of the power grid.

In activities like back country trips in areas without cell phone coverage or in a widespread emergency with the loss of our normal means of communication we can use satellite phones, but this technology is very expensive, requires subscriptions and there is no guarantee that the complex infrastructure of satellite communications will work under all circumstances. The obvious solution for Ham Radio operators will be to switch to shortwave communication using battery operated radios and often NVIS modes of operation. NVIS stands for Near Vertikal Incidence Skywave, which means transmitting with special antennas straight up to communicate with other stations 30 km to 300 km (20 to 200 miles) away with low power – which would be the most useful communications distance if help is needed. We could use SSB voice communications, but this requires that the person we want to reach is sitting constantly at his or her radio to be able to receive the message. This can be a problem: In a real emergency we probably won’t have time for this. We could instead use capable digital modes with automatic message handling capabilities like JS8Call, but these require notebook computers or other complicated setups in the field which consume a lot of energy and can be difficult to recharge off-
grid on a reliable basis.

Evgeny UA3AHM/OH5HM and Sergej UA9OV have developed another mode of digital shortwave communications, which aims to be easy to use, capable and – most importantly – friendly to the operator’s resources. Apart from a low power battery operated transceiver and a small digital interface, only an Android smartphone is needed, which can be recharged with cheap and readily available consumer-grade solar chargers. Evgeny and Sergej have created an app called “HFpager” which allows to use the smartphone’s sound chip to encode and decode audio signals in the SSB audio passband of the transceiver – similar to PC based modes like FT8 and JS8Call. It uses rates of transmission of 1.46, 5.86, 23.44 and 46.88 Baud. Modulation is 18-tone Incremental Frequency Shift Keying (IFSK) with forward error correcting Reed-Solomon code RS(15,7) and a superblock by 4 RS blocks with interleaving.

Click here to continue reading the full article.

Click here to check out the HF Pager Android App.

Thank you for the tip, Pete!

The CR Kits FT8 DSB Transceiver: Some preliminary information

Many thanks to Pete (WB9FLW) who notes:

Adam BD6CR of CR Kits is getting close to releasing the FT8 DSB Transceiver. Below is some preliminary information:

D4D: A simple QRP transceiver for FT8

Adam Rong, BD6CR

D4D stands for DSB transceiver for Digital modes. It is a Double Sided Band transceiver kit designed for digital modes, especially for FT8. If have chance to try FT8, you will be amazed by the strong decoding capability offered by the communication protocol, digital signal processing and software. I still remember clearly a YouTube video by W6LG who communicated with bulbs. I started to think how much the transceiver could be simplified if you have a moderate antenna like a full sized dipole or EFHW.

A DSB transceiver is much simpler than a usual SSB transceiver, however it was never used for FT8 as far as I know. I did some experiments on my Choc perf board. I started with a direct conversion receiver for FT8 and it worked okay. Then I made a DSB transmitter and the transmitted signal can be decoded. By referring to the designs of AA7EE, VK3YE and ZL2BMI, I combined them using only one NE602 and a PTT switch and it gave me success to make a few FT8 QSO’s.

Personally I really enjoyed it because a manual PTT switch will save power consumption and circuit complexity, but you will need to well sync with computer, although it was not really a problem for me. Per request from a few hams, I found a VOX control circuit and modify the hold time to be compatible with FT8, and I put them together and made a few improvements on the signal purity and frequency stability, and it became our D4D. Do we have to worry about the unwanted Lower Side Band? Maybe, but for a transmitter of 1-watt, it is not really a big problem. Is it just a toy for a transmitter of 1-watt and only half of the power will be effective? Not really, as I can easily make a few QSO’s as far as 1500 miles range for 40-meter band.

Here is the brief specifications I have measured (subject to change without notice):

Summary: Crystal controlled single frequency DSB transceiver for 20m (14.074MHz), 40m (7.074MHz) or 80m (3.573MHz), other frequencies could be added per request
Power supply: 10-14V DC regulated power supply or battery pack, 12V is recommended, center positive, reverse polarity protection available
Current consumption in RX: 15mA
Current consumption in TX: about 260mA(?) at 12V, and about 300mA at 13.8V
RF output: about 1W for 20m band at 12V, a bit more for lower bands like 40m and 80m
Spurious suppression: no worse than -50dBc
Antenna connector: BNC connector, 50 ohm
Audio in connector: 3.5mm mono, at least 600mV to activate VOX, connects to headphone connector at PC sound card, no dedicated PTT connector is required
Audio out connector: 3.5mm mono, connects to microphone connector at PC sound card
Amber LED: TX status
Green LED: RX status
Frequency stability: Okay for FT8 mode per test. If the optional heater resistor R20* is added, after warm up of about 3 min, long term frequency stability in 10 min will be improved at the cost of acceptable short term frequency stability sacrifice in 30 sec.

Let us briefly go through the circuit: The input audio will activate the VOX circuit of D2 (1N4148), Q5 (2N3906), Q6 (2N3904), Q7 (2N3904) and Relay. The relay is a DPDT type and controls both antenna and power supply. The LPF consists of L2, L3 and surrounding capacitors, and it is switched to either transmitter output or receiver input. The power supply is polarity protected by D1 (1N5817) and switched to either receiver circuit or transmitter circuit. The receiver circuit is only for audio amplifier consists of Q1 (2N3904) and optional heater resistor R20*, while the transmitter circuit is for RX muter Q8 (2N3904), TX driver Q3 (2N3904) and TX final Q4 (BD139). X1 is a filter in the receiver front end to help eliminate strong broadcast interference, and X2 is the crystal for the built-in oscillator in U1 (NE602). U2 (78L05) is the 5V regulator for U1, and Q2 (2N3904) is a buffer amplifier in the TX chain.

Thanks for sharing this, Pete! What a simple transceiver concept!

We’ll post updates as they become available.

Click here to view CRkits.com.

FT4 digital mode now available in WSJT-X release candidate 5

(Source: Southgate ARC)

The new amateur radio digital mode FT4 is now available for download as part of WSJT-X Release Candidate 5 

You can download wsjtx-2.1.0-rc5-win64.exe (or for other O/S) from near the bottom of the page at 

FT4 Protocol document 

See the WSJT Group at 

New digital mode: Joe Taylor (K1JT) has announced FT4

(Source: Southgate ARC)

Joe Taylor K1JT has announced a new digital mode, FT4, which is 2.5 times faster than FT8 

FT4 is an experimental digital mode designed specifically for radio contesting.  Like FT8, it uses fixed-length transmissions, structured messages with formats optimized for minimal QSOs, and strong forward error correction.  T/R sequences are 6 seconds long, so FT4 is 2.5 × faster than FT8 and about the same speed as RTTY for radio contesting.  

FT4 can work with signals 10 dB weaker than needed for RTTY, while using much less bandwidth.

FT4 message formats are the same as those in FT8 and encoded with the same (174,91) low-density parity check code.  Transmissions last for 4.48 s, compared to 12.64 s for FT8.  Modulation uses 4-tone frequency-shift keying at approximately 23.4 baud, with tones separated by the baud rate.  The occupied  bandwidth (that containing 99% of transmitted power) is 90 Hz

Further information on FT4 is at