NUE-PSK Digital Modem


Answers to your Frequency Asked Questions!



How many Hz are represented by each vertical line on the display?? How many lines wide would represent an "ideal" signal? How many lines wide would be enough to indicate that the transmitting station might be overdriving their radio?
     The display covers from 500Hz to 2500Hz in 128 steps. This equates to 15.625Hz per vertical line. An ideal signal (idle) would be 2 lines wide. When sending data, the width is greater since additional sidebands are generated. However, since the vertical scale is logarithmic, the width can be even wider yet just above the baseline. When the peak is several lines wide, the signal is probably being overdriven at the transmitter (or possibly in the receiving stations receiver).


Some of my contacts are asking how I'm copying their signal and what the IMD is, etc. I was told mine was 19. I assume they meant -19 but how are they measuring it? Is 19 good or bad?

     An IMD of -20 is generally considered good. -30 is excellent. An IMD of -19 could mean that you are slightly overdriving the transmitter audio input. Try turning down the TX Audio control slightly.  On the other hand, an IMD may not be accurate when significant noise is present. IMD is calculated using the strength of the idle signal (ignoring any sidebands) as a reference. The ratio of the strength of the first pair of sidebands outside the desired idle signal to the desired idle signal, in dB is the usual quoted IMD. -20 dB means that the undesired sidebands have a power level that is one percent of the desired signal. -30 dB means that the undesired sidebands are one-tenth of a percent of the desired signal.
     At -10 dB, the undesired sidebands are 10 percent of the desired. If the noise level is significant, it may be impossible to determine accurately the level of the undesired sidebands. Instead, the software may be reading the noise level (at the frequency where the undesired sidebands are expected to be found) instead of the undesired sidebands. If the noise at that frequency is stronger than the "undesired sidebands", an erroneous IMD will be calculated. For example, it might report -19, when the actual IMD should be -25.
     The measured IMD at the TX Audio output of the NUE-PSK modem is about -50 dB. To achieve a transmitted IMD of -20 to -30 dB requires a "linear" transmitter. Overdrive of either the audio, or rf, portion of the transmitter can result in nonlinearity and a reduction in the IMD of the transmitted signal. On most rigs this means that there should be little or no ALC indication when transmitting. ALC readings usually indicate that the peaks of the transmitted signal are being reduced to control the transmit power level--this can lead to nonlinearity. Consequently, it is recommended that PSK power levels be set below 40 percent of the rated power of the rig. I usually tune my rig for normal rated power on CW/SSB with the power control set for 100%. I then adjust the audio level from the modem to obtain a power level that is 10 to 25% of the rated power. For example, with my 5W FT-817, I set the audio level to obtain a power of about 1 watt when using F12, or 2 watts when using F8. (F12, with no keyboard or macros, transmits the "idle" signal. F8 transmits a CW signal. The CW power is about twice that of the PSK idle signal)


Missing callsign in the macro?  Having entered various macros containing my callsign, I toggled to TX to send my macro, and I got a reply from a Dutch station. I then noticed that I had still my portable callsign stored under Ctrl-M.  I changed this entry Ctrl-M, but now there is no callsign appearing when the macro is run. This applies to both savings Ctrl-M and Ctrl-T.  (I type hb9zap and close it with < CTRL-M >. The ALT-M and Alt-T remains empty !!)
     Is the modem in receive mode when you type the callsign, followed by Ctrl-M?  You cannot save a callsign, either your own, or "theirs" while in transmit mode.  Your callsign is saved in EEPROM (using Ctrl-M), while "theirs" (using Ctrl-T) is in data memory. This means that "theirs" will be lost when cycling power. However, your callsign should remain in EEPROM when the power to the modem is removed.


RF getting into the modem and causing problems?

     You might have RF getting into the keyboard controller via the keyboard cable. Some keyboards have cables that are not shielded. If this is the case, you might try a Radio Shack clamp on RFI choke (Split ferrite toroid--not exactly round--it's square).
     If you don't have a good counterpoise, you may have excessive RF voltage near the transmitter and modem.


My IC-706 doesn't have a 6-pin mini DIN jack on the back for the data connection!

     If you have one of the earlier 706's (not the MkIIG) you must use a 13 pin DIN connector for the modem data connection to the rig. The IIG has both 6-pin miniDIN and 13-pin DIN connectors. So it sounds like you need a cable with a 13-pin connector on it if you have an early model 706.

TS-440 radio connectors

     The 6-pin DIN (not mini-DIN) ACC1 on the TS-440 is for computer control (basically RS232/TTL), not for connecting an AFSK modem or TNC. You must use the 13-pin DIN connector to connect to the NUE-PSK modem. (The connections to the 6-pin ACC1 are shown on one of the schematic pages.)
     The newer TS-480 uses a 6-pin mini-DIN connector that uses the same hookup as the Yaesu FT-817/857/897 rigs.


I'm not getting the correct responses when I run the prog program for connecting to the modem serial port

     Which interface are you using? Sparkfun? Wulfden? other? And if you are using the Sparkfun CP2102/3, do you have the driver installed?
     Did you verify that the com port you are using (com3) shows up in the Port information in Device Manager? And, is it the port that you have the programmer attached to?
     The error message that you report is because the bootloader code could not establish a connection to the serial port you specified. You can download Application Note AN1094 from the Microchip website. It lists all of the error messages that the bootloader software can generate.


What is the "Prog" program for the PC?  Can it run on Linux?

     "Prog" is a special program that knows how to read Intel Hex files and to handshake with the bootloader that is programmed into the NUE-PSK modem, while transmitting the hex file to the UART in the modem. It supports a few commands such as Read from a selected location in the dsPIC Flash program memory space, and Read from EEPROM (our dsPIC does not have internal EEPROM). Since it runs in a "DOS Window" on the PC, if the Linux system can emulate the DOS Window, it will likely run on that system.
     "Prog.exe" is "16-Bit Flash Programmer.exe" that may be found on the Microchip Website. It is described in Application Note AN1094. Source code for both the host (PC) and dsPIC are available from the website. Note, however, that the application note describes a bootloader placed in dsPIC program memory just about the interrupt vector tables. In the NUE-PSK modem, the bootloader code is placed at address 0x15000 and above. In addition, the dsPIC bootloader code has been modified to test for the presence of a button push before launching the bootloader. If a button press is detected, the bootloader is launched. The bootloader then waits for UART activity, for up to 10 seconds. If no activity is found, the Modem application is launched. If there is activity, the dsPIC bootloader and the PC host software "handshake" and establish communications between the two (at a 115.2kbps baud rate).
     The program "16-Bit Flash Programmer.exe" can be run without modification. However, since the source code is available, it can be modified and recompiled. The windows code is in Visual C and C++. This code can likely be converted to be compiled with some of the Linux based development tools. Since I am not a Windows program developer, I have not attempted to anything with the host code. Instead, I used the compiled .exe code for this project.
     In addition, the bootloader and the NUE-PSK code are treated as two separate "projects" in MPLAB, but in a single "workspace". This requires a non-standard method for generating code that will be loaded with an ICD2 (simultaneous loading of both the bootloader and the NUE-PSK application). Also, extra steps are required to produce a HEX file for application code that does not contain the bootloader. This file is needed when using prog.exe (16-Bit Flash Programmer.exe) to load new code into the Modem's dsPIC.
     I hope that this answers some of the questions about "prog.exe". I can not claim ownership of this code as it was obtained from Microchip.
     In the near future, we will provide a "Developer's Toolkit" that will have more information for those that wish to develop their own code for the Modem.


Making the Serial Cable

     BEWARE!  For all of you that are anxious to download new software to the NUE-PSK modem--PLEASE DO NOT USE THE NUEPSK112A.HEX file that is contained in the dsPIC Source Code zip file on the NUE-PSK website.
     BEWARE!  This file was not intended for use with the field programmer, but instead with the Microchip ICD2 programmer.  If this file is used, you will wipe out the bootloader memory and will render the modem inoperable until it is reprogrammed with an ICD2.
We apologize for any inconvenience this may cause.  If anyone has already tried this and found that the modem no longer works, please let us know.


Signals are not appearing on the modem as received from my transceiver

     I suspect a connection problem. Are you sure that the connector is fully inserted into the Radio connector at the modem. These connectors are a tight fit and, if not fully seated, may not have a good connection.
     If you are sure that this is not the problem, can you try patching a signal from the earphone or speaker output of your rig to the radio connector on the modem? Connect the audio signal to pin 7 of the 8 pin miniDin receptacle on the side of the modem. Pin 7 is the middle one on the top row, when looking at the right end of the modem. Connect the ground of the rig to the ground of the modem. Pin 6 of the modem connector is ground. Pin 6 is the top left on the connector. Or, if you remove the cover of the modem, there is a ground test point near the upper right corner of the PCB. If you set your rig for a normal listening level, you should see the spectral display on the modem.    
     You need to have Modem Audio In connected to Radio Audio Out.  Likewise, Modem Audio Out must be connected to Radio Audio In.

Recommendations for a nice, portable keyboard?

     I have purchased a BTC9118 PS2 keyboard from Fry's Electronics. It measures about 6" x 12". Cost about $18. It works fine with the NUE-PSK Modem.
     I also purchased the 2366 keyboard on EBay (from Hongkong). Cost $3 plus $10 shipping. It is a combo USB/PS2. Since it requires at USB/PS2 adapter (which comes with it), I decided to transplant the cable from an old mouse to the keyboard. This eliminates the need for the adapter. I have had no problems with this keyboard. However, there have been a few messages about possible problems.
     The 2366 keyboard measures about 4" x 8.75". If you Google on "2366 Keyboard", you should find the eBay ads.
     In addition to these two, I have used the Roll-Up keyboard from All Electronics, and another larger roll-up that I purchased from Discount Electronics in Austin, TX. The All Electronics keyboard is also a combo USB/PS2. It does work with the modem.
     If you purchase a keyboard, and experience problems with it, please notify George, N2APB via the NUE-PSK website ( We have been testing revised code for the keyboard controller that should handle almost any problem that could arise with the keyboard (assuming that they conform to PS2 specs). If you test a keyboard and find that it works with the original keyboard controller chip, then there is little need to replace the controller. (Note--the keyboard controller chip is mounted beneath the LCD in the modem and is a DIP package plugged into a
DIP socket. It is not soldered in.)

     I also purchased and regularly use the Parallax PS/2 keyboard (p/n 32351 at  This is the one that was pictured in the QST photos, and it's got the best size/feel combination for my use on the bench.  Some guys have discovered that Parallax uses several different suppliers for the electronics part of the keyboard, and some of them experience the problems with the NUE-PSK ... but are solved with the revised code we have for the modem's U5 chip.
     The Cherry keyboard is small enough (not as small as the 2366), the key spacing/size is great and it comes with a moisture resistant shield. It's PS/2 only, inexpensive, and has been tested with the NUE-PSK.


Activating the modem's "Boot Loader" program

     Turn on the modem power switch while pressing the Select button.  Hold the Select button in only as long as it takes to turn on the modem power. Then, within 10 seconds, press Enter on the PC keyboard to launch the programmer code on the PC.
     Holding the Select button, while powering up the modem, starts the bootloader code in the modem. It has a built in 10 second timer that will launch the modem application if no data is received on the serial programming port of the modem. Perhaps you held the Select button too long. The programming code that is run on the PC can also timeout if something prevents the modem from acknowledging the attempts to send info to it, such as no electrical connection, or the modem may not be running the bootloader code.


Holding the modem up at an angle for easier viewing

     You might also want to look at the "Clam Shell Mounting Bracket" at All Electronics. They are adjustable, cost $1.50. The part number is CMT-2.  I have one attached to the underside of my Modem with Velcro strips, and use small rubber stick-on feet on one base of the shell. Each of the two bases that make up the clam-shell are about 2" x 2".
I purchased a Staples black wire mesh business card holder and it works great, and looks good.  It is also very light weight and is not very fragile, so is easilty packed for mobile activities.  $4.49 in the store and am very happy with it.
     Now for all you cheapskates out there there's another business card holder stand also at Staples for $2.99 its made of painted folded sheet metal, and doesn't look anywhere as nice but does the job equally well.


Differences in keyboard current requirements

     Most of the mini-keyboards that I have tested draw less than 5mA. Some of the early IBM keyboards could draw 100mA or more. It has been a while since I checked the current on my BTC9118 (6" x 12"), but as I recall, it was about 3mA. Of course, if the LEDs were illuminated, this current would be 30mA (or more) higher.


Battery Life

     Please note that the capacity of standard alkaline 9V batteries range from about 400mAhr to 625mAhr, depending on manufacturer. In addition, the terminal voltage of alkaline batteries drops nearly linearly as they are depleted. If one uses these in the NUE-PSK modem, and leave the backlight turned ON, the initial discharge rate with fresh batteries will be about 60mA. As the terminal voltage of the batteries drops to 12, the discharge rate increases to about 85mA. Further depletion of the battery voltage causes additional increases in the discharge rate to about 100mA when the terminal voltage of the two batteries in series drops to about 9V.
     Note also that rechargeable 9V batteries typically have a much lower capacity--<250mAhr.
     If we assume a rate of 60mA, a 500mAhr battery could conceivably run for a bit over 8 hrs. However, at a discharge rate of 100mA, the best that could be expected would be 5 hrs. Therefore, I would expect that something close to 5 hrs for fresh batteries could be achieved.
     Please refer to the QEX article for a chart showing the modem power requirement versus terminal voltage of the battery. Note that the current is significantly less when the backlight is turned off. If you are operating with internal 9V batteries, this is the recommended mode. If you want to run with the backlight turned ON, it is recommended that you run with an external Gel cell.
     In addition, there are 9V lithium cells available (Ultralife) that have a much higher capacity, if internal batteries are required, especially if the backlight will be left ON.


Desire for keyboard-generated CW

     If you want to run keyboard CW, you might want to take a look at what John Fisher, K5JHF, has done with his Morse Code Device. This little beauty, converts keystrokes into perfect on/off keying. John's board is only about 2" x 3" and uses a small Freescale microcontroller. It has a standard PS2 jack for the keyboard, and a few pushbuttons to control speed, etc. It also allows recording and playback of macros and runs for hours on a coin cell. I have used one for Field Day. It's an excellent device for the CW operator. One of the fellows in our local QRP club even installed one inside a keyboard. For information, check the AQRP yahoo group and John's files.


Caps Lock, Num Lock and Scroll Lock functions do not work on the keyboard

     These are not supported functions for the keyboard when used in the NUE-PSK modem. It is up to the host (in our case the dsPIC) to determine whether to act on those key presses. At this time, we have chosen to NOT implement these features. During the "Power On Self Test-POST" of the keyboard you will see the corresponding LEDs flash on and then off. This is part of the POST for the keyboard. It takes a command from the host to make these LEDs stay on. It is also up to the host to decide what to do when one of these keys have been pressed. Since PSK actually sends faster (due to Varicode) when using lower case characters, we chose to not implement Caps Lock. For the few times when a Cap is needed, you can use Shift.

My battery gets hot!!!

    A couple instances have popped up for some modem owners discovering that the Battery Mod ( was not completely done on their unit as received from us.  One of the symptoms is that the upper battery gets very hot because it is shorted to ground.  We're sorry if you experience this problem.  It's an easy thing to check for and correct, if needed.
      If you remove the small battery compartment plate on the bottom of the enclosure and then remove and unclip the batteries, you can peer at an angle into the compartment and see the underside of the pc board.  Close to the edge of the board you will see the "trace cut", or lack of it which is causing the problem in these few instances.
      What you *should* see on the pc board is what is shown in Photo B on the web page referenced above (or directly at ... the cut might be made anywhere along that trace that connects the 1st and 3rd pads.  It might be a nice grind made by a Dremel, or it could be some slices made with a razor knife.
      Further, if you are so inclined, you could use a DVM to measure the resistance between those two pads (1st and 3rd positions)  They should be "open".
      So if the trace cut is not there, or if it wasn't made well enough (i.e., if you see continuity between those pads), then you could either remove the pc board from the enclosure and make a good trace cut yourself, or return the modem to us for immediate repair and return. 
      The ultimate "test" for if your unit is okay is to plug 9V batteries into their clips.  If both batteries remain cool moments after clipping them in, you're probably good-to-go.  You could also then check the battery voltage by using the Select pushbutton to bring up the CONFIGURE menu, and rotate the TUNE control counter-clockwise until you see "Battery Voltage".  The tap the Select PB again and you should see something between 14-18 volts displayed, depending on the condition of your batteries.
     We apologize if yours was among the few modems that slipped through our test and QA process prior to shipment.  Just let us know if you have any heartburn at all and I'll immediately help you out.


How can I tell if the pcb mods were made at the factory?

     A quick way to verify the battery modification -- Connect two 9V batteries. Turn the power on. Plug a power connector into the external power jack (non-powered wall-wart or just a plug). If the power goes off, the modification has been made.


The modem loses the custom changes I make in Configuration whenever I turn off the power ... is this right?

     This is expected. We are considering saving all user selected parameters in a future software update. At present, these settings are lost (except for the defaults) whenever power is cycled.


Can't seem to get my callsign entered into the modem memory.

     While in RX, enter your callsign and then press Ctrl-M.  Now press F11. You should see "de AB7OC" displayed on the screen.


Does the pre-fab "modem cable" you guys sell work with multiple radios?

     Yes, the pre-made cable we sell works with Yaesu FT-817, FT-857, FT-897; Icom IC-706, IC-706, IC-7000; and the Kenwood TS-480 transceivers.  We are considering making cables for use with other popular transceivers as well.


The Select pushbutton is too close to the edge of the hole in the top half of the case, and sometimes it binds.

     You can adjust the position of the pc board within the enclosure, and hence the distance of the Select pushbutton to the hole in the case.  First, remove the top half of the enclosure and loosen the nickel-plated screws on the bottom of the enclosure.  While pushing the pcb toward the lower left direction, re-tighten those screws on the bottom shell.  Next, loosen the screws holding the pcb to the standoffs on the top of the pc board.  While pushing the pc board to the lower left, re-tighten those screws on the pc board.  Put the top half of the enclosure on again and attach the four black anodized screws, while simultaneously biasing the top shell as far to the right as possible while re-tightening the screws.  These actions will give enough clearance to the Select pushbutton to the edge of the enclosure hole, thus eliminating the binding condition.


Pressing the Pause-Break key on the keyboard causes the modem to reset.

     Yes, this is a small bug in the modem software and it will be fixed in the next software update.  Until then, refrain from pressing the Pause key - there is no related function for this key.


What is the PGA setting used for in the Configuration menu?

     PGA stands for Programmable Gain Amplifier, which happens to be U7 in the schematic. This device can be set to different levels of amplification to better handle either low-level or high-level audio signals coming into the modem from the transceiver. Normally there is no need to change the setting of the PGA. The default setting is a voltage gain of 16. The PgUp key can increase the gain to a maximum of 32. The PgDn key can decrease the gain to a minimum of 1. In some cases, with a very strong signal near a weaker signal that you are trying to copy, reducing the gain may help in decoding the PSK signal. An alternative (which I frequently use) is to reduce the RF gain of the receiver, so that there is little AGC action due to the very strong signal. Because of the limited dynamic range of the electronics, reducing the gain, or the signal level of the input, can prevent "clipping" of the audio signal in the Modem. Generally, you will find that the Modem will demodulate signals that are barely visible on the spectral display.


When should the Hi-Drive jumper be used on the pc board?

     The modem ships with the little red jumper only on one of the pins at the small 2-position P1 pinheader in the upper corner of the modem pc board.  In this "off" position, the Tx Audio signal generated by the modem goes through an internal 10K resistor, thus lowering the audio levels delivered to the transmitter, making the drive level more appropriate for a transmitter's "mic" input.  Jumpering the two Hi-Driver pins with the little red jumper effectively removes the 10K resistor from the audio path, thus raising the driver level to "line" input levels (~1V RMS).


How do I enter an F11 or F12 function key when using the "2366" keyboard?

     Look at the bottom left corner of your 2366 keyboard. There should be a key with a Green "Fn" label. Notice that on the F1 and F2 keys there are Green F11 and F12 labels, respectively.  Press the Green Fn key and the F1 key for F11.  Press the Green Fn key and the F2 key for F12.


Why don't you provide the serial interface adapter by default with the modem?

     None of the adapters are made specifically for the NUE-PSK modem. Most have solder pads for +3.3v, Ground, Transmit Data and Receive Data. A cable would have to be soldered to these pads. The other end of the cable needs to have a 4 conductor plug on it that connects to the 4 conductor header in the battery compartment of the modem. The Ground pad of the programming adapter must be connected to the ground of the modem. The TxD line of the programming adapter must be connected to the RxD pin of the modem. The RxD line of the programming adapter must be connected to the TxD line of the modem. If using the homebrew adapter show in the QEX article, the 3.3V line of the adapter is connected to the 3.3V line of the modem. If using one of the commercial adapters, the 3.3V connection to the modem can usually be left unconnected. In fact, if the programming adapter receives its power from a USB connection, or RS232 connection, then the trace labeled "X" on the schematic in the Operators Manual should be cut.
     If you don't have a background in electronics, I would suggest that you solicit help from a local ham that has experience in making up cables for connecting pieces of electronics together.

How does the AFC function work?  When should I use it?

     Here is a brief note regarding AFC on the NUE-PSK Digital Modem.  This should be of particular interest to those that want to leave the Modem frequency fixed, and tune the rig.  AFC (Automatic Frequency Control) consists of two parts: Capture and Tracking.
     Capture is part of the Acquire routine. It is initiated whenever tuning has ceased for a fraction of a second, or when the Select button is tapped, or the "End" key on the keyboard is pressed. This reduces the initial error in frequency between the internal numerically controlled oscillator, and the audio frequency of the signal you wish to decode. Since many rigs can tune only in steps of 10Hz or greater, it is nearly impossible to set the frequency close enough for decoding to occur. The Acquire routine "captures" the desired signal by adjusting the numerically controlled oscillator to within a few Hz of desired signal. For this reason, the frequency displayed on the modem may not stay at 1500Hz. It may differ by several Hz. (Also note that the cursor can move only in discrete steps-- 128 to be precise-- representing the audio frequency range from 500Hz to 2500Hz. The frequency of the numerically controlled oscillator can, however, be set with much greater precision). If you are lucky enough to have a rig that tunes in 1Hz steps, it would be possible to turn off Capture, but it would likely take more time to get sufficiently close to the desired signal frequency for decoding to occur. Capture reduces the initial time delay before decoded characters begin appearing on the LCD.
     Tracking is an optional feature. When AFC ON is selected (the default), the numerically controlled oscillator continues to track slow changes in the desired signal frequency. This allows for slow drifting, in either your rig, or the rig at the other end. If both rigs are "stable" then AFC OFF may be selected. I prefer to leave AFC ON.
     Selecting AFC OFF does not disable the Capture operation.


German keyboard generate some swapped characters when displayed

     I believe that the problem is due to the keyboards generating a particular scan code based on the position of the key, not the label on the key. Consequently the German keyboard generates the same scan code, when pressing the Z key, as the US keyboard does when pressing the Y key--and vice versa.
     A table is used in the modem to convert the scan codes to characters displayed on the LCD. This table could be modified, but we would then have to keep up with multiple versions of the software. The simplest solution is to use the US keyboard. Modification of the table would require that you reprogram the modem with another version of the software. Do you plan on obtaining a serial interface to allow software upgrades? If so, we can consider providing a special version of the code.


If your keyboard "doesn't work"

     As more of you are coming online now with your new modems, we are seeing a greater variety in the kinds of keyboards that are being used with the modem.   These bargain basement keyboard deals come along in all sizes, shapes and quality/performance characteristics ... and frankly, some do not meet the standard, published PS2 "specifications" for signals and timing.  Such is the joy of depending on "standard" components working with your product :-) 
     This variability in the cheaper keyboards has been causing us some restless nights, as we have been trying out different approaches to the software in our keyboard controller chip (U5 in the schematic).
     We indeed think we have widened the timing and logic enough to accommodate the "errant keyboards" that are popping up here and there, and we're ready to start supplying a replacement chip to those who think they need one.
     ==>> We posted a new article on the website concerning "Keyboard Information", and it describes the 4 or 5 things you need to be sure you know in regards to what a "good" keyboard is, before we determine that you have one of these "misbehaving" keyboards.
     So please, take a look at the article at and see if your keyboard really is "not working".  Perhaps you just need to place the modem into TX mode first, whereupon *then* you will then see the keypresses echoed to the display.   Or perhaps the keyboard cable connector isn't plugged in all the way into the modem (it's a tight fit).
     Only after you are sure you are doing everything right, you can drop me a note at the address indicated on the web page and we'll arrange getting you a replacement chip.
     NOTE:  If your modem is currently working fine with your keyboard, THERE'S NOTHING YOU NEED TO DO.  You're sittin' pretty.  But if you have a keyboard that you simple *must* use, and it's not responsive with the modem, then check out the article and contact me at that address on the web page.

The "basics" for expected keyboard operation

        1) Ensure that the keyboard plug is firmly plugged in.
        2) Make sure to the keyboard is plugged in before you initially turn on the modem power (mandatory for keyboard initialization)
        3) Make sure your keyboard is either a PS2 type or a combination PS2/USB type.  (A pure USB type keyboard will not work.) 
     Testing the keyboard is easy, even without a radio connected ... just hit the F12 key to get into TX mode (see "TX" at the top of the display), and the keys you press will be echoed to the LCD's lower lines.


Software Developer's Kit ... coming soon

     There is already lots of flexibility with this design and we are hoping that others will want to contribute features and capabilities via the open nature of the modem source code.
     We are preparing a "Software Developers Kit", or SDK as we say in the industry, that provides detailed information on the development environment, programming conventions, and product architecture ... all of which will enable developers to hop right in and modify/extend the application software in the modem box.
     We have already overviewed in our articles some of what you are asking, but to briefly recap ...
         1) We use the MPLAB "Integrated Development Environment" (IDE), freely available from Microchip. 
         2) We use the C30 Compiler plug-in, Student Edition, which is also freely available from Microchip.
         3) We use the Microchip ICD2 "In-Circuit Debugger" as a programming and debugging pod that plugs into the 2x3 pinheader on the modem board.  This programming hardware plugs into your PC's serial port and works in conjunction with the MPLAB IDE to erase, program and debug the program in the dsPIC on the mode.  The ICD2 costs $159 from Digi-Key (p/n DV164005-ND).  There are some cheaper programming pods available (e.g., the PICKIT) that just do programming, but I haven't used that in a while and probably won't be describing it in the SDK.
      It's really not too difficult a learning curve for a programmer who is familiar with embedded programming to get his head around this project.  With the software architecture (again, already described a bit in the QEX article) and the general dsPIC programming and computing capabilities in hand, one could fairly easily hop in and start making simple changes to get comfortable with his ability to customize what we already have present.  (e.g., change the sign-on message, give a beep when the rotary encoder is turned, hard-code your own call into the unit for the automatic exchanges, etc.) 
     Then, once greater confidence is gained, making bigger, more functionally-oriented changes become possible.


I need another standard (unterminated) cable like what you guys send with the modems by default

     It's easy to get more cables just like what we ship standard with each modem order. You can order a 6' cable with the 6-pin connector on each end for about $3.50+shipping, straight from the supplier we use: Jameco ( It's their p/n 10604. And what we do is cut the cable in half to produce two unterminated cables suitable for use with the NUE-PSK modem. I just checked and they have them in stock.


Connecting the modem to the Elecraft K2 transceiver

     Jean-Francois just yesterday posted some information on his K2 interface.  It's a nice one that includes amplification and isolation.  See
     Elecraft has some very nice PDF articles on their website - look for "PSK31 Interface" or "Data Mode Interface", and you'll see some equally nice designs.  Most are simple.
     Since there is no standard connector, per se, for interfacing a digital modem to the K2, you'll end up homebrewing your own solution. 
     For my own K2, I put a 6-pin miniDIN jack into one of the existing holes in the rear panel, and wired it as if it were an FT-817.  This way I could use the same cable as I use for my FT-817 (!).  On the inside, I wired the Audio in modem signal over to the headphone jack.  I wired the Audio Out modem signal over to the Mic AF input pin (through a 10:1 voltage diver), and I wired the PTT line over to the PTT line on the Mic jack.  (Of course, all these wires are on the inside of the K2.)  Works just fine for me.  I will ultimately implement one of the amplifiers specified in those interface references I mentioned, so I can tap audio off the AF detector in the K2 signal chain, and thus not have to hear the audio all the time.)
     You could achieve the same functional effect by plugging a 1/8" plug into the headphone jack and using a standard 8-pin DIN plug wired for the audio in and PTT, plugged into the Mic jack ... both on the front panel.  Pretty easy.


Right side of LCD display sometimes "goes blank"

     We believe we have a fix for the "disappearing right half" of the display.  It is a timing issue that comes about in the control of the chip selects for the left and right sides of the display. (The LCD has two controllers and we need to access each in quick succession when drawing a line or when writing text that crosses the midpoint boundary.)  The fix is being tested, and if it works it will be included in the first software update that will be issued soon.


Checking out the keyboard and PTT line to the transceiver

     1) Are you plugging your keyboard in before applying power to the modem?  (required)
     2) Pressing F8 toggles "Tune" on/off in the display?
     3) Pressing F12 toggles "TX" on the display?
     4) Pressing keyboard character while in TX mode echoes the characters to the display?
     5) Is your radio cable plug firmly pushed all the way into the connector?  (It could be a hard press until it gets "broken in a little bit" - just make sure you press it in straight-on, without wiggling the plug too much.)  There's a chance that the PTT connector pin wasn't making it all the way into the jack.
     6) Do you see any receive signals displayed on the spectrum line of the display when in receive mode (i.e., when not in TX mode)?  Of course you would need to tune the rig to some PSK31 activity, typically around 7.070 MHz around this time of the evening.
     7) Test the PTT line at the modem connector ... if it is not working, the modem cannot put the FT-817 into transmit mode.
          a) Conditions: modem powered off, the keyboard plugged in and the radio cable disconnected,
          b) Stick a couple of wires (clipped off component leads, whatever) into pins 6 and 8.  (Looking at the jack on the modem, pin 8 is "top row, leftmost hole" and pin 6 is "top row, rightmost hole".)
          c) Grab your DVM and set it to read resistance.  Connect the DVM red leads to the wire sticking out of pin 8 and the black lead to the wire sticking out of pin 6.
          d) Turn on the modem, and you should see an open circuit reading on the DVM. 
          e) Press F8 to put the modem into the Tune mode and you should see a shorted circuit indication on the DVM.  (Note, you might need to swap the DVM leads to get the proper indication. This "closure" of the internal FET controlling the PTT line shows that the modem is functioning enough to put the rig into transmit mode.)
     8) Test the PTT line at the end of the cable ...
          a) Conditions: modem powered off, keyboard and radio cable plugged in.  Cable not plugged into FT-817.
          b) Put the black connector on the end of the cable into a vise or some fixture to hold it steady, giving you access to the pins.
          c) Turn on the modem
          d) With the DVM in resistance mode again, *carefully* place the red probe onto pin 2 (bottom-right pin) and the black lead onto pin 3 (middle left pin).  See an open indication on the DVM.
          e) Press F8 on the modem keyboard and measure the pins on the end of the cable again.  This time you should see a shorted condition between pins 2 and 3.


Caution for using the +V wire in the modem cable

     The +V line on the J3 "Radio" connector of the modem is intended to either:
            1) provide the supply voltage of the modem to the transceiver, or
            2) to accept supply voltage from the receiver (or external supply in the same radio cable.)
    So in the case you describe of wanting the modem to supply power to an SSB transceiver, the main limiting factor of "how much current can be supplied" is the power switch S1, which is rated for 100ma at (30V). I suspect that S1 could safely handle perhaps about 300ma without problems at 12V, but I probably wouldn't want to go higher than that.
    Now the good news is that the PSK-xx transceivers from Small Wonder Labs take about 100ma in receiver and 250ma in transmit. Or at least that's what my particular PSK-xx boards need when properly tuned and driven from the NUE-PSK.
    The power could legitimately go "either way" in such a set-up. Since the whole idea of providing the +V line at the connector and in the cable is to eliminate one power cable in the portable station. That is, instead of having a power cord going from your external battery to *both* the transceiver and the modem, you just have *one* power cable going to the modem and have the modem cable supply power to the PSK-xx transceiver. Or you could have the power cord going to the transceiver and have the modem cable carry the supply voltage over to the modem.
    Frankly, the second way is what I am set up to do if/when my two 9V batteries in the modem are exhausted. I use these the PSK-xx in my own portable PSK station and have the gel cell powering the PSK-20, and then have the modem cable supply the battery power over to the modem. This way, there's no concern about exceeding the current rating of the modem power switch, or any pins/wires in the cable. Plus this configuration also reduces the possibility of any "digital hash" from the modem from getting into the transceiver signals, although it's unproven (to me) that it's even a valid worry.
    Two things to remember, though ...
        1) You cannot have a power cord going to *both* the modem and the transceiver if you have the +V line in the cable connected. (Or if you do, just cut the "y" jumper on the modem pcb by J3.)
        2) You ought not try powering anything from the modem when using the internal batteries. There's not enough current capacity in the batts to do anything except power the modem.


Is there a faster way to tune around the spectrum on the modem LCD?  

     Try increasing the Tune Increment to "Double" in the menu accessed by the Select pushbutton.  Provides for getting up and down the audio spectrum much faster than the default "single" setting.
      Also, the keyboard's up/down arrows work similarly at a 2x rate as compared to the right/left arrow keys.


My pre-fab cable seems bad - I don't get any signals to/from the rig

     Chances of the cable being bad are very slim, as the one supplied with the modem is a molded pre-fab 8-pin miniDIN connector on it from the factory.   Perhaps you mis-identified the "Type A" or "Type B" nature of the cable, as it makes a difference for the color codes and signals on the wire.  Carefully check your cable against the diagrams on the backside of the QUickStart sheet provided with your modem, or also at  Once you have identified whether you have an A or B cable, then you can try connecting those signal wires to the proper position in the plug you have going into your rig.
     Speaking of which, what rig are you attempting to interface the modem to?  Most rigs we've heard used with the modem have experienced good success with audio levels coming in.  If needed, you can boost the gain of the audio input channel coming into the modem, by using the <PAGE  UP> key ... see the manual for further details.
     When you see very low signals on the modem's LCD, do you hear lots of digital activity form the receiver audio?  Of course there must be sufficient band activity for the modem to operate, and if late at night and the band is out, not too many signals will be heard on 20 or 40.
     When you dial over to one of the signals  do you hit the <ENTER> key, or pres the Select pushbutton on the modem to attempt locking onto the signal?  Sometimes it takes several moments of receiving solid signals before the modem controller is able to lock onto the signals.


What is my actual transmit frequency when using the modem?    

     The quick answer is that the actual transmit frequency is either the sum or difference of your rig's dial and the modem Tune dial. 
     We believe there is a convention to use the upper sideband injection, which makes it easy to determine the actual frequency as the SUM of the rig dial and modem dial.  So if your rig is set to 7070 kHz and you have the modem set to its initial power-on audio frequency of 1.5 kHz, then your Tx frequency is 7070 + 1.5 = 7071.5 kHz
     Not sure of the IC703 digital mode options, but on the FT-817 one can specify using either "upper" or "lower" sideband injection. On Menu 26 we select PSK31-U, or USER-L if you are using some filters in the rig. This way the actual operating frequency is just the sum of the audio frequency as shown on the modem, and the frequency shown on the dial of the rig.  If you use xxx-L, you have to subtract the modem displayed frequency from the frequency on the rig to get the "true" frequency.


Popular PSK Frequencies"    

    I think they are 20m (14.070) in the daytime, and 40m (7.070) in the early evening.
    80m (3.580) has started to become more active, and I've been using the Warbler more often than ever on this band.
    10m (28120) is really dead ... but this is going to be the band for our Dayton adventures with the NUE-PSK modems.  (Recall the "walking advertisement" thread we had a couple weeks back.)


Making the Serial Cable

     You'll recall from our literature that the NUE-PSK Digital Modem may be upgraded to newer software in the field (that is, by *you*) simply by connecting the serial port of your PC to an adapter, which in turn plugs into the "Field Upgrade" connector in the battery compartment of the modem.  Then with the proper program running on your PC (available for free download from the NUE-PSK website) you can send the modem the latest-and-greatest software we supply on this NUE-PSK website.  This is a great way to keep your modem up to date with the latest features and bug fixes!

     The USB or RS-232 serial interface adapter that you do get will probably need a cable to connect it to the modem's "Field Programming" port -- the 4-pos'n, 0.1" pinheader "P5" on the bottom side of the modem pcb, as accessed from the battery compartment.  You can fabricate a simple four-wire ribbon cable terminated on one end in a mating SIP connector (Mouser p/n 517-974-01-04, as shown on catalog page  The other end would connect to your SparkFun, HVW, or custom-built adapter.  (Note, the Wulfden adapters do not require this serial cable, as their adapters plug directly into the modem connector.)


Where do I get one of those serial interfaces?

     Again from the QST and QEX articles, we mentioned that we do not provide a serial interface with the modem purchase because everyone's computer and way of operating are different.  There are some great products out there and you can purchase specifically just what you need for about $20 from a number of good vendors.  Based on what kind of serial port you have on your computer, you will want to purchase a USB-to-TTL interface or an RS232-to_TTL interface. Of course you could instead homebrew a simple one-IC version of the interface right from the schematic we provide in the manual and in the articles, thus saving you the purchase of the adapter.  

     Any way you get there, the interface adapters are available from ...

1) Wulfden at Hawk's Mountain --

2) SparkFun Electronics -- (USB)

3) HVW Technologies -- (USB), (RS-232)


Transmitter Settings Guidance for Digital Mode Operation on the FT-817

(May be similar on FT-857 and FT-897.)
1) Set the rig to a PSK31area of the band (e.g., 14.070 MHz) and set the rig operating mode to DIG (use arrow buttons above the display).
2) Set the rig's power level to be full 5W output. (Tap the F key, dial to the PWR MTR screen and tap A button repeatedly until you see the 3 bars blinking. Tap the F key again to exit.)
3) Select "PSK31-U" in rig menu #26 DIG MODE. (See the "Note" paragraph at bottom.)
4) Set the "Digital Mic" level to 50 in rig menu #25 DIG MIC.
5) Connect the rig RF output to a power meter with a dummy load attached.
6) Put the modem into TUNE (press F8) and adjust the TX Audio control to obtain about 3 watts of output power. Press F8 again to turn off the modem TUNE mode. (Since TUNE produces a CW signal, the BPSK signal will be somewhat lower on average, but will peak to this level at times.)
7) Use the CONFIGURE menu of the modem (press-hold the Select pushbutton) to read the Tx Audio level. It should be in the range of 15-20% at the default, power-on modem frequency of 1500 Hz.

     If You Don't Have a Power Meter - You can also adjust the Tx Audio output to the proper level by viewing the ALC meter bars when the modem is in TUNE mode. Starting with the Tx Audio control fully counter-clockwise, turn it up slowly until you just barely see the first ALC bar appear, then back it off slightly until it just disappears. This should also yield the same 15-20% Tx Audio reading in Configuration as obtained in step 7. (Make sure you are still using a dummy load.)
     Determining Signal Quality -- If you have an additional receiver, you could use Digipan on it to view the waterfall and get an IMD reading on your modem-generated signal. (Use an attenuator or disconnected the receive antenna to ensure that you are not overloading the receiver.) A reading below -25dB indicates a good setup of the modem and transmitter. You might try adjusting for great power output in step 3 above if you can verify that the signal has an IMD reading of least -20dB and set up to monitor the quality of the BPSK signal, you should not try to go much higher than 3 to 4 watts in TUNE. It might be possible to run higher power, say up to 4 watts in the TUNE set above, but only if you can verify an IMD of -20dB or less.
     Note: Convention seems to suggest using "PSK31-U", as recommended in step 2. This way the actual operating frequency is just the sum of the audio frequency as shown on the modem, and the frequency shown on the dial of the 817. If you use xxx-L, you have to subtract the modem displayed frequency from the frequency on the 817 to get the "true" frequency.


The batteries won't fit!!!???

     The standard 9V batteries do indeed fit, although admittedly it's a tight fit and you need to angle them into place -- no force required (and no hack saw!), but just a little trial and error. We've put together two resources that might help you and others in the future when it comes to installing the batteries.
    1) Web Page -- Description and close-up photos showing the technique. Even has a little bit of the background on our unusual choice of batteries for this project.
    2) Instructional Video -- A highly trained and NUE-certified professional is shown installing batteries to the NUE-PSK Digital Modem.
Good luck, and Power On!


Programming the Macros

The Macros section in the manual might be a little confusing to the uninitiated.  Here is some simple guidance on programming macros into the modem ...
Turn off the modem.
Turn on the modem.
Enter your callsign on the keyboard.
Press Ctrl-M to record your call sign.
Press F11.
Hopefully you will see "de [your callsign]" without the extra callsign.

F11 displays the CWId string (assuming that you have recorded your callsign as noted above).
When you record your callsign, using Ctrl-M, it adds the "null" character to the EEPROM after your callsign.
If you have previously recorded your callsign, at Powerup, the modem copies that callsign, along with "de" into a RAM location for use as the CWId string.

If the above works, you should be able to re-record your Macros
Use Alt-Fn to erase the Macro.
Ctrl-Fn to start recording a new Macro.
F9 to stop recording.

A note about the EEPROM.  Once it is recorded, it stays until overwritten. When you "erase" a Macro, you are really just writing a "null" character in the first location allocated for that Macro. The "null" character is used as an "End of Macro" signal. Ending Macro recording with F9, simply writes a "null" character after the last recorded character.



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Page last updated:  May 2, 2008