NUE-PSK Digital Modem

A digital modem for PSK31 and RTTY field use ... without a PC! 
CW and Keyer modes also now supported!


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Parallax mini-keyboard not recommended

Version 5 Command Reference Sheet
and the updated Hot Key Map

CW Direct Mode in v5 software

Hardware Mods for kit builders

Hardware Mods for modem owners

Using "Upload / Download Config"

Assembling the Lower Chassis

Loading the Latest Software

Making the Serial Cable

ICD2 Programming Cable
for Software Developers

Notes for Kit Builders

Battery Life Study

Odd Keyboard Behavior?

HC908 Programmer for U5

Frequently Asked Questions


Use modem with CW paddle
... instead of keyboard!

CW Direct mode (ATS-3)

CW Direct Mode (Elecraft KX-1)

Custom NUE-PSK Flash Drive available
Perfect for use with the USB card option

System connections on the side panel
(Click for larger view)

PC board holds all components
9V batteries fit neatly inside the enclosure.
(Click for larger view)

Production PCB
(Click for larger view)

Production PCB
(Click for larger view)

Highly-trained and seasoned designer checkout at the factory (W8NUE)
(Click for larger view)

"Did I actually order the wrong-sized screws?!" (N2APB)
(Click for larger view)

Cover of QEX for Mar-Apr 2008
Cover photo features use of the (no longer recommended) Parallax mini keyboard.  Read the entire 12-page article here.

Portable PSK31 station:
(top) Transceiver (FT-817)
(middle) NUE-PSK Modem
(bottom) "2366" Keyboard
(Click for larger view)

80m Warbler + NUE-PSK Modem station:
(top right) Warbler 80m PSK31 Transceiver
(top left) NUE-PSK Digital Modem
(bottom) Dauphin PS2 mini-keyboard
(Click for larger view)

Try out the IW7EHC "Menu Reference Label"
Just print, cut it out and paste to the top of your modem!
(Click for larger view)

Place an Order

(Click on photo for larger view)

Featured in QST for March 2008 (download article)
Featured in QEX for Mar-Apr 2008 (download article)
Winner of Circuit Cellar Magazine's "Design Contest 2007"
Featured in new ARRL CD: "Digital Technology for Emergency Communications Course


   Version 5.03d adds "External Monitor" capability

Version 5 software adds built-in keyer! and CW Direct Mode!

Version 4 software adds CW Mode

USB+RTCC Card Details

Place an Order

Available Accessories:
USB+RTCC card, interface cables

NUE-PSK Digital Modem

An easy and portable way to get on the air with PSK-31, RTTY and CW ... no computer required!

    The NUE-PSK is a small 7" x 4" x 1" standalone, battery-operated digital modem using a graphic display for transmit and receive text data, as well as for showing band spectrum and tuning. Just plug in a standard PS2 keyboard and connect to an SSB-capable transceiver like the FT-817 or the PSK-xx transceivers from Small Wonder Labs, and you'll have an effective digital mode station that goes absolutely anywhere.

    The NUE-PSK modem is an "open" design, with published hardware details and software source code.  What this means is that many others can contribute to the modem's capabilities and modes of operation.  Already we have a "USB add-on option" that maintains the current time and date, and lets you record the QSO (with a timestamp) to a USB stick for archival or EmComm use. 

    Further, the modem has the ability to be "field upgraded" by using a serial port (or USB thumb drive) to load new versions of the modem software.  The NUE-PSK Modem supports BPSK (PSK-31), QPSK, RTTY and CW.  Just download the latest-and-greatest modem software from this website and send it to the modem over the serial port.  It's the modem that keeps on growing ... new modes, new features, new add-on accessories!

Updated:  March 24, 2015

> Version 5.03d Software Available ...  We added External Monitor (MON) feature to send the modem’s Tx and Rx data characters to the modem’s type ‘B’ USB serial port (square jack on the side of the modem case), in addition displaying them on the modem’s LCD.  This feature, toggled on/off by the ctrl-E keystroke, shows “MON” at the right side of the modem LCD when active, and allows modem data to be sent to a terminal emulator program running on a PC, and thus may allow the operator to more easily view  the incoming and outgoing modem data.  Notes:  (1) The PC’s serial port must be set to 115 Kbps N81, no flow control.  This may be set in the terminal emulator application running on the PC;  and (2) A USB flash drive containing a new “ftrfb.ftd" file must be inserted to the modem upon initial power-up in order that the modem’s USB controller chip is updated to the correct version. (See Latest Software files below for this ftrfb.ftd file.  Thanks to Milt W8NUE for this great feature!

> SDR Cube Transceiver ... an SDR transceiver that is optimized for digital mode operation with the NUE-PSK Modem — Want another easy way to take your digital mode operation to the field?  Check out this companion to the NUE-PSK modem: a portable, Software Defined Radio transceiver that also does not need a PC to work!  It's a fully self-contained CW/SSB/AM transceiver with some amazing features that make it great for the digital modes when used with the NUE-PSK.

Technical Resources

The Latest Software: Pick your favorite way to load the software from the options below ...
- mem.dat --
Right-click and "Save as" to computer, then unzip and put mem.dat onto a thumb drive.  Then use use Flash Bootload feature with optional USB card
- modem_5.03.hex -- Right-click and "Save as" to your PC. Use serial adapter with PC Bootload feature (Loading software)
- modem5.03(modem+lowboot).hex -- Right-click and "Save as" to your PC. Use serial adapter with PC Bootload feature to update old v1.xx modems only) (See Loading software)
- modem_5.03(full).hex -- Right-click and "Save as" to your PC. Program modem controller with ICD2 programming pod and MPLAB
- Modem Source Code v5.03 -- Source code for the dsPIC controller (useful for developers)
- USB controller ("ftrfb.ftd") firmware -- Version 3.68, required for modem v5.03 use.  (Place this file onto Flash drive and pwr-up modem with drive inserted.)
- RTCC Source Code v1.10 -- Source code for the PIC controller on the USB card (useful for developers)
- Source Code for U5 -- Source code for the MC908 keyboard processor code in U5 (useful for developers)
- S19 binary for U5 -- Binary for the MC908 keyboard processor code in U5 (useful for developers)

Release Notes

Config.txt -- Place this latest file on your flash drive and do a Download Config on your modem to set your EEPROM to the latest settings.

Master Flash Files --  Collection of useful files for modem owners using the Flash drive with their USB card option.  When downloaded and unzipped onto your thumb drive, you'll have all the latest manuals and software loads for convenient use with your modem.  See the README.TXT file in the zip collection for details.

Mem_Image Utility -- This is the PC utility for converting hex files exported from MPLAB to the standard mem.dat format suitable for loading from Flash Drive on the USB card, using the modem's Flash Bootload command.  Usage format is simply "mem_image  filename.hex".  [NOTE:  This is a developer tool and is not needed by most modem owners.]

Video Clips:
- Prototype Operation
(5 minutes, 47 MB .wmv file)
- Video Clip: Battery Installation  (2.5 minutes, 20 MB .wmv file)

Tips on Installing the Batteries

- QST --  March 2008
- QEX --  Mar-Apr 2008
- ARRL/TAPR 2007 Digital Communications Conference -- Article and Slides

- NUE-PSK Modem Overview ... Here's an updated PowerPoint slide deck that overviews the PSK fundamentals and design highlights of the NUE-PSK Digital Modem.  Great for using at the next gathering of your radio club!
- CW Mode Technical Slide Deck -- Presented at the TAPR Digital Communications Conference on Sept 16, 2011.

- Operating Manual v5 (full manual) --
Full, self-contained manual for basic modem, CW, keyer and RTCC module.
    - Operating Manual v5 Addition
- Operating Manual v4
- Operating Manual v3
    - Operator's Manual 2.33  plus
Insert 2.33
    - Operating Manual 2.10
    - Operating Manual 1.34
    - Operating Manual 1.30
    - Operating Manual 1.20
    - Operating Manual 1.10

- Keyer Mode quickStart Guide --  for version 5 software
- CW Mode QuickStart Guide --
Quick 'n easy guide to CW Mode operation.
- CW Mode Technical Overview --
Slide deck presented at the TAPR Digital Communications Conference on 9/16/2011

- QuickStart Guide --
Everyone gets this 1-sheeter with their modem purchase. This is the latest version.
- Command Reference Guide --
A very handy 1-sheet summary of the modem & USB commands
- USB+RTCC Quick Assembly Guide (rev B2) --
Instructions for assembling the "rev B2" USB+RTCC card.
- USB+RTCC Quick Assembly Guide (rev B1) --
Instructions for assembling the "rev B1" USB+RTCC card.
- USB+RTCC Quick Assembly Guide (rev Ax) --
Instructions for assembling any of the "rev A" USB+RTCC cards.
- RTCC Upgrade Kit  --
Guide for adding the RTCC parts to existing USB cards
- Radio Cable Guide --
How do you connect to your rig?  Cabling details shown for over 50 radios.
- Kit Assy Manual --
This is how you assemble your own modem.
RTTY App Note -- Useful guidance for using the new RTTY mode on the modem.

IW7EHC "Menu Reference Label" v1.20 -- (PDF or DOC) -- Just print, cut it out and paste to the top of your modem!

Developer Resources:
- EEPROM Memory Map --
These files (xls and txt) describe the fields used in the nonvolatile memory on the modem pc board.  This memory contains the modems settings and macro test strings.
SDK Manual -- For developers of custom software.

Important Notes:
Power Supply Modification -- Modems first into production can benefit by applying these simple mods to allow powering the unit from an external supply without removing the batteries. (Modems purchased from Jan 1, 2009 do not need to worry about doing this mod!)
- Standard Radio Cable Supplied with all Modem Purchases -- See the linked page here for information about the 3-foot radio cable supplied with your modem. It is important to understand if you have a Type A or Type B cable so you know how to attach the connector for your SSB rig.
- Supplying Power to/from the Modem -- This is a caution note for use in wiring your own connector for the cable to your transceivers ... be careful how you handle the +V line on the end of your cable.

PSK31 is one of the latest communications modes to capture the interest of hams worldwide. Its inherent ability to dig out low, near-inaudible signals is ideally suited for low power QRP enthusiasts. The PSK31 digital modem engine, however, requires intense DSP processing that is only commonly available in PC sound card. Thus the PSK operator desiring portability for field operation is locked into using a laptop computer as a controller, which results in a cumbersome station. But there’s hope!

The NUE-PSK is a standalone, battery-operated digital modem using a Microchip dsPIC33F microcontroller. The project uses a single graphic display showing transmit and receive text data, band spectrum, and tuning indication. When coupled with an SSB-capable transceiver and a standard PS2 keyboard, the NUE-PSK Digital Modem forms an effective, compact, and portable station for working the digial modes on the amateur bands.


>    Standalone, half-duplex modulator/demodulator for amateur radio digital mode communications

>    Handheld unit ... no PC required

>    Menus select operating modes, Squelch Thresh, PGA Gain, CW ID

>    128 x 64 pixel graphic LCD displays audio signal spectrum 500 Hz to 2.5 kHz (with backlight)

>    Tx and Rx buffers and menu system displayed in lower half of LCD using four 20-character lines of text

>    Tune controls modem position along audio spectrum

>    Modes currently supported: BPSK31, QPSK, QPSK reversed

>    External keyboard jack: 6-pin mini-DIN, PS2-compatible

>    Standard PS2-style or dual-mode USB/PS2 keyboard (user-supplied) provides text input for Tx entry, command/mode selection and modem frequency adjustment

>    Connection to SSB transceiver: 8-pin mini-DIN (audio in, audio out, PTT, power)

>    Powered by two internal 9V batteries (not included) or an externally-applied supply via 2.1mm coaxial jack

>    Power requirements: 9-18V DC.  Current at 12V is 60 ma without backlight, 80mA with backlight.  The current decreases as input voltage is increased.

>    Field reprogrammable to allow software updating in the field by the owner

>    Aluminum enclosure provides for rugged portable use while shielding transceiver from digital EMI

>    Enclosure dimensions: 7" x 4" x 1"

>    Single 3.75" x 5.25” pc board contains all components and connectors

>    Lightweight: < 1 lb with batteries.

>    Control for precise audio level control to transceiver 

>    Cable assembly provided (plug and shielded cable) for connection to the SSB transceiver
Optional USB Card provides ability to record transmit and receive text from QSOs for archival and printing.  Also serves as serial adapter port for connection to PC for upgrading modem software, and for uploading/editing/downloading file with modem settings and macro text strings.



As illustrated below, a dsPIC33F is at the heart of the project design. This highly-integrated dsPIC33F device employs a powerful 16-bit architecture that seamlessly integrates the control features of a Microcontroller (MCU) with the computational capabilities of a Digital Signal Processor (DSP). The resulting functionality is ideal for applications that rely on high-speed, repetitive computations, as well as control … just perfect for the NUE-PSK Digital Modem.

A complete description of the NUE-PSK Digital Modem design and operation is provided in our cover article in QEX for March-April 2008.

(Download full-resolution PDF version of the schematic)

Parts List for Homebrewers:

Download BOM as Excel Spreadsheet


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Page last updated:  March 24, 2015