Tag Archives: FT4

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)

BD6CR @ CRKits.COM

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

Conrad packs the Elecraft KX3 and AX1 for a New York City POTA Rove

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


New York City Park Rove, December 30, 2022

Conrad Trautmann, N2YCH

After being bitten by the Parks On The Air (POTA) bug, I became an activator in early 2022. I was hooked. Digital, and specifically FT8 & FT4, is the mode I prefer. A lot of experimentation ensued until I was able to refine my POTA setup to an Icom IC-7300 powered by a Bioenno 20ah battery mounted in a four rack unit Gator case and a Buddipole dipole antenna on a push up mast.

As a radio broadcast engineer by trade, I was very focused on maximizing performance and coverage and after much refinement and trying different things, I feel like my POTA kit performs well. I’ve made contacts as far away as Indonesia, Japan and Israel using the POTA setup in a park… so mission accomplished.


The POTA kit above is not something I can easily take with me on a business trip however, especially by air, so I turned my sites to a Xiegu G90 and various end fed half wave antennas and fiberglass masts and more Buddipole parts to pack into my carry-on luggage. Now I could activate parks wherever I could fly to and I’ve completed successful activations in Wisconsin and Georgia.

Still, I needed to pack a second bag and check the luggage to do these trips. What I really wanted was something I could carry on the plane with me.

I knew I had to change my point of view on what I could achieve using a portable kit. A small radio and antenna wasn’t going to get me contacts in Indonesia, but I could transmit far enough to have someone hear me and get my ten contacts to activate a park. Researching my options online constantly brought me to videos and blog posts here on QRPer.com. Thomas loves his Elecraft KX2 and in a few field report videos he demonstrates an Elecraft AX1 antenna connected directly to the radio for some fast CW POTA activations. This setup was appealing because of the size and he always has a successful activation.

I researched the Elecraft options and the KX3 seemed like the right radio for my digital activations. It has a DATA mode, it can run split operation, it’s got a wideband filter setting and while Elecraft only recommends 5 watts for data modes, it can do up to 10 watts. I managed to find and purchase one gently used on eBay.

I installed the Pro Audio Engineering Kx32 aftermarket heat sink to be sure I protected the final output transistors from overheating and use a Signalink model USB SLUSBKX3 as a sound card interface to the computer. The Signalink can key the radio using the audio keying feature, but I chose to use the Elecraft KXUSB cable to use CAT control and let WSJT-X key it instead. It also allows WSJT-X to read and control the radio’s frequency for easy band changes. I have a Bioenno BLF-1209A 9Ah battery to run it rather than use the internal batteries and I haven’t come close to running the battery out on an activation yet.

Then I bought the Elecraft AX1 antenna with the 40 meter AXE1 optional antenna extender and the AXT1 tripod adapter. It is tiny. There’s really no other way to describe it. It’s a little, baby antenna. Fully extended, it is about four feet tall. I was highly skeptical of how this might perform given its size. I’m using a 25’ Buddipole RG-58 A/U 50 ohm MILSPEC-17 cable terminated to BNC connectors to get the antenna away from my computer because I’ve found that RF and USB do not play well together. I typically try to get the antenna situated in a nearby spot, with a little distance between it and the computer. I bought the Maxpedition Fatty Pocket Organizer Thomas suggested on QRPer.com and a little Amazon Basics Lightweight Mini Tripod.

The AX1, the adapter and tripod all fit in the organizer with room to spare and it fits into a backpack with the radio, battery, cables and my Lenovo Thinkpad 3 laptop. I’m also able to fit in the the Bioenno battery and laptop chargers. At the urging of my XYL, I also have a printed copy of my license in the backpack, too. I haven’t had to show it to anyone yet, but I’m ready, just in case. The backpack is a Mindshift model 18L, designed for photographers, but is easily adapted to contain all of the components I need for a portable activation. Here’s a photo…

So now I’ve got a completely self contained POTA kit in a backpack that can be carried aboard a plane. Continue reading Conrad packs the Elecraft KX3 and AX1 for a New York City POTA Rove

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 
http://physics.princeton.edu/pulsar/k1jt/wsjtx.html

FT4 Protocol document 
http://physics.princeton.edu/pulsar/k1jt/FT4_Protocol.pdf

See the WSJT Group at 
https://groups.io/g/WSJTX/

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  
http://physics.princeton.edu/pulsar/k1jt/FT4_Protocol.pdf