Important Note:  Unless you are absolutely certain that you know what you are doing, do not perform this conversion.  
I cannot be - nor  will  be - responsible for any damages to your radio incurred as a result of your reading this website. 

A Dual VFO, Digital Display and Internal Keyer for Your Ten-Tec Triton 540 
1. Introduction

    Although this site currently describes how this DDS VFO can improve the Ten-Tec Triton 540, it may be readily installed in other Ten-Tec radios including the Corsair I and Corsair II, the 'Omni's', the Delta, the Argosy II and the Digital Century 21 as these radios are all equipped with a factory stock digital display.

    However, if the user is willing to install a home brew digital display
(the AADE DFD1A is an excellent choice), other Ten-Tec radios like the analog Century 21, the Century 22 or the early Argonauts could likewise reap the benefits of this conversion. Exciting Stuff!

Note: This VFO could also be housed in a metal enclosure and serve as a versatile dual VFO for those reluctant to modify their Omni, Triton, TR7, etc and / or don't want to take the time (and expense) to rebuild the mechanical PTO.  Here's just one example.

2. Parts - Itemized Component List

    For the DDS VFO itself, you'll need about $60 - less if you have a well stocked junkbox.  The most expensive part is the optical encoder.  I found nice ones on eBay for $20 each.  

Note: a 128 step optical encoder will enable a frequency excuirstion of about 5 khz for each complete rotation.  A 256 step encoder will double this to 10 khz.  Either is totally satisfactory and there are most often economical choices on eBay.

   The P/C boards have been designed so that the Chinese AD9850 DDS board can be soldered right to it.  Here are pictures of the schematicthe P/C board 2 artwork, the wire connection points and a completed assembly.

3. Conversion Suggestions - Ten-Tec Triton 540 Radio

    The Analog Triton (540) does not have an internal digital frequency display.
So, if you plan to undertake this conversion, you'll need some form of digital frequency display as the PTO, the circular frequency marker and the slide rule dial will all be gone - removed!  While one could possibly find a used external Ten-Tec digital display, I decided to mount an Almost All Digital Electronics DFD1A device within the radio and on the front panel (more later).

    a) Disassembling the Triton
    b) Removing the PTO and Crystal Calibrator
    c) Pretesting and Mounting the Controller

Before installing, ensure that your DDS VFO board works properly.  Following the schematic, connect up the encoder, a frequency counter to the output and then 12 VDC and ground.  You should see a 5.000 Mhz signal (or something very close) which should change as the encoder is rotated.  If you don't have a counter, your station receiver will suffice.  You can even connect it directly to your Triton at the rear jack provided for a remote VFO.

Important Note: The DDS VFO output level should be set (using R5)close to the output of the Triton's PTO as the Triton's circuitry was designed around this value.  Setting the DDS VFO's output higher than this will generate 'birdies' and needlessly increase receiver background noise.  The Triton's PTO's output is approximately 1.5 Volt peak to peak.    If you have a 'scope, use it to set the DDS VFO's board right on the money.  If not, just turn R5 slowly until the radio begins to receive properly on all bands, but no higher.
Also Note: If you monitor the signal on your receiver, you'll hear a rough, warbling note.  This is normal as the OFFSET / RIT connections have yet to be made and the processor's A/D converter (used for the RIT function) will be 'hunting' a bit. Ground the RIT Disable pin and the 'wandering' should disappear.

      I mounted my DDS VFO in the space occupied by the Noise Blanker.  I removed the plug-in terminal strips and wiring, except for the red lead which I used to power the DDS VFO.  I rerouted the coaxial cables to effectively bypassing the Noise Blanker, and then carefully drilled two mounting holes - one for the voltage regulator and another diagonally across for another grounded mounting.  I placed a piece of perf board between the DDS VFO board and the chassis to eliminate the possibility of any short circuits.  I also installed a small terminal strip for a series wound toroid filter  to reduce any spurious signals from 'riding' the 12 volt line and to keep RF out of the DDS VFO. The board is very securely mounted with good ground connections.  

    While you are drilling the holes, make another one at the base of the DDS VFO board and equip it with a grommet.  This hole will be required for the 4 offset leads and the transmit lead going to the R lead on the Offset board.

     If you plan to install the Jackso Harbor Press PK4 keyer, then drill another hole just above the DDS VFO mounting area and equip it with a 3 inch 4-40 screw and several nuts (to set the mounting position), as shown here.  This screw will provide a good ground for the PK4.

Note: If you want to retain your Noise Blanker, the DDS VFO and the PK4 keyer may be installed elsewhere - say on a small, well grounded platform above where the crystal calibrator resided.  You should then be able to find a suitable location for the DFD1A board.

  Mount a small terminal strip on the inside of the VFO enclosure as shown here.  Using a 4-40 screw, you can 're-tap'  the existing screw hold that secures the coaxial grounds on the other side of the VFO enclosure so that the new 4-40 screw can hold both terminal strips.  Once done, run a short piece of coax from the output of the DDS VFO - through the small hole in the VFO enclosure - to the new terminal strip and terminate the shield to ground.  The 2 white leads will be connected together to the coax center conductor on an adjacent terminal strip pin.  This makes for a very stable connection.

    d) Installing and Connecting the Optical Encoder

    The easiest way is to place a small metal plate (drilled for your encoder and mounted in the existing PTO mounting holes) on the outside of the radio's sub-panel.  Install your encoder (finger tight) and then the front panel.  If you can attach the tuning knob of your choice, and if it spins properly - OK!

    In most cases, however, you may have to mount the optical encoder on the front panel with this 
small metal plate (I used a scrap of double sided P/C board) and then cut away at the sub-panel so that the optical encoder will fit (tin snips will suffice).  This is what I had to do with my Triton.
e) RIT / OFFSET Functionality

    The wires from the OFFSET switch are currently connected to the Control Board which is on the top side of the chassis.  Our goal is to reuse the wiring from the Control Board to the OFFSET control, re-routing them to the DDS VFO board underneath.
f) Installing the Digital Display Controller - Repurposing the Crystal Calibrator Activation Switch

My  AADE DFD1A board is mounted in the space vacated by the crystal calibrator, and the LCD display is mounted on the Triton's sub-panel.   First, remove the two circuit boards on the other side of the chassis and carefully drill two holes for the 4-40 screws that will support the DFD1A circuit board.  Install a piece of perf board (Radio Shack) between the two stand offs created by the 4-40 hardware.

    Assemble the DFD1A board using the instructions provided in the kit, mounting the pin header and other wiring connections as well as the LCD contrast and TXCO trimmer resistor on the component side of the DFD1A board.  The board is assembled this way to provide access to these points after the board has been mounted on the perf board.  I used wire straps to hold it in place.  

    The DFD1A makes for an exceptional digital frequency readout.  However, when connecting it up to the Triton 540, a switching mechanism needs to be provided to 'tell' the counter if it should be 'counting' up or down.  Rather than drilling another hole in the radio's front panel, I opted to use (repurpose) the existing push / pull switch on the RF gain control, the one that was used to activate the crystal calibrator.

Important Note:  If the DFD1A is used with the Triton 544 to replace its digital display, there are existing bandswitch contacts to provide automatic 'up / down' display switching.

    This switch provides 12 VDC to activate the calibrator, but the DFD1A requires a grounded connection.  The actual switch connection on the rear of the RF Gain control has a 12 VDC tie point (4 wires) on one lug, and a voilet wire on the other.  This is the violet wire that runs to the previously removed crystal calibrator board.   The 12 VDC tie point needs to be removed and a ground substituted.

    Carefully unsolder all 4 wires from the switch, solder them together and cover them with 2 layers of heat shring tubing

    Then connect a wire from the spared terminal to ground, as shown here.

    Verify with your meter that operating the switch provides a solid ground on the violet wire, and then connect the violet wire to the appropriate point on the DFD1A board.  Connect the power and ground leads from the DFD1A module to the 12 VDC connections on the DDS VFO board.                                                                                                                 

    I used the 'Biggie' display provided by AADE.  It fits nicely in the narrow space between the chassis and the front panel.  After carefully measuring and drilling the holes, I mounted the display with 4-40 hardware.

Note: The 5 volt power to the LCD is provided by the regulator on the DDS VFO board through a 10 ohm resistor.

    Since the space between the chassis and front panel is mininal, I was not able to use pin headers.  Rather, I soldered the 30 gauge wire directly to the holes in the LCD.  Once the wiring was done and double checked, I provided several layers of plastic tape to guard against shorts and then mounted the LCD.  The wiring back to the DFD1A board was run through a newly drilled - grommet equipped - hole in the front.

    Using a short length of RG-174 coax, connect the outout of the Triton's VFO to the input of the DFD1A counter through a 100 pf ceramic capacitor. Hold off on reinstalling the front panel as it needs to be reworked a bit.

    Hint:  It's not necessary to ground pins 10, 9, 8 and 7 on the LCD.  A ground connection between pin 1 and pin 5 will suffice.

g) Reworking the Front Panel

   Remove the plexiglass panel and the 3 incandescent bulbs.  A function button needs to be installed on the front panel to switch VFO's, activate / deactivate the SPLIT mode, and so forth.  Additionally, optional status LED's may also be installed, but I decided not to install them at this time.

    Were even the smallest push button switch installed flush with the front panel, a corresponding hole is needed in the sub-panel.  I just removed the OT LED and drilled out the opening to accommodate a miniature Radio Shack normally open push putton switch (Crazy glued in place).  Connect one lug on this switch to ground and the other to the trace on the P/C board that goes back to the OT lead.  DO NOT CONNECT IT TO 12 VDC.

    Next, remove the OT TR board and snip the OT-LITE wire right at its connection lug.  Remove both the Control and SSB GEN boards so that this lead can be run (through an existing plastic grommet) to the DDS VFO board on the other side of the chassis where it will be terminated on the button lead,
as shown here.  Once done, reinstall the insulators and the boards themselves.  Don't turn the power on yet.
h) Reinstalling the Front Panel

    Ensure that the leads for the optical encoder are run properly (no kinks or snags). Connect the 3 wire plug for the ALC lamp and then place the panel in place, securing it with the bottom screws.  Using your meter, verify that the push button - when pushed - grounds out the button terminal on the DDS VFO.

i) Testing the Controller
4. Commands

    When powered up, both the A and the B VFO will be set to the lower band edge, that is, 7000, 3500, 1800, 28000 (etc).  VFO A will be enabled.  The user may then tune with VFO A in the normal manner, and VFO A will be used for transmitting.  If the RIT (OFFSET) switch is activated (pulled out), the receive frequency will vary based upon its setting; the transmit frequency will not change.  When the OFFSET is turned off (pushed in), the original frequency will be restored.

    To switch to VFO B, tap the FUNCTION button and the system will be using VFO B.  The frequency previously stored in VFO A will not be changed.

        Note: if you have wired up the optional LEDS, the LED for either VFO A or VFO B will be illuminated.

   To enter the SPLIT mode, just tap the FUNCTION button twice (a short followed by a longer tap - like a ' A' in CW) and the radio will enter the SPLIT mode.  The on-line VFO will control reception, while the off-line VFO will control transmitting.

        Note: if you have wired up the optional LEDS, the SPLIT LED will be illuminated.

    To exit the split mode, tap the FUNCTION button twice (another short - long tap sequence) and the radio will revert to the normal mode.  The contents of the on-line VFO will be copied into the off-line VFO.

    To LOCK the system at any point, just hold the FUNCTION button down for 2 seconds and the system will be LOCKED, and cannot be changed until UNLOCKED.  To unlock the system, just tap the FUNCTION button - and that's it!  While LOCKED, the RIT control will work.

        Note: if you have wired up the optional LEDS, the LOCK LED will be illuminated.  

    An optional button has been added dedicated to the SPLIT function.
 Tap it one time and the SPLIT function is active.  You can then use the main button to switch between the VFO's.  Tapping the SPLIT button again will disable the split function and map the on-line VFO into the standby unit.

    To store the last used frequency before powering down, operate the LOCK function, release the button and push it again within one second.  If you have equipped the LED's, they will all flash 3 times to indicate that the frequencies (VFO-A, VFO-B and the split function) have all been stored in flash memory and will be available whenever the radio is next powered up.  

5. How the Software Works - The 30,000 Foot View - click here

6. On-the-Air Results

a) Receiving

    The P/C board is mounted under the chassis, and it works quite well for me. With a tuned antenna connected and the preselector properly peaked, there are a few detectable narrow banded (200 to 300 khz spurs).  The louder spurs are asterisked. 
Note: This 10 meter spur (28975 khz is quite loud) is a known Triton issue.  To tune this frequency, set the bandswitch to the 29 Mhz position and tune downward. Check the service manual for more information.
 b) Transmitting

   To be determined............

8. Other Concerns / Considerations 

    If the user decides to tune up the antenna to make a QSO (say, answering a CQ), and if the antenna SWR is too high - the power supply circuit breaker could trip.  Since the DDS board is powered by the same supply, the desired frequency will be lost when the breaker is reset.  This is one of the drawbacks of using DDS in lieu of the analog PTO when the DDS is powered by the current sensing / protective power supply.  

    Three solutions are possible. 
  1. The DDS board could be powered separately - say by a wallwart supply - and left on all the time.  This way, should the Triton's power supply trip out, the desired frequency information will be retained on power up.   Gauche? - yes, but fully workable.
  2. If the AIRPAX (or equiv) circuit breaker used to safeguard the radio's finals were to be installed in the Omni proper, then the DDS VFO could be powered on the 'line side'.  This way, the circuit breaker's tripping would not cut the power to the DDS VFO module.
  3. Alternately, the operator may gradually increase output power (using the drive control) when tuning up to an antenna.
9. Using an External DDS VFO Controller - Front, Side, Rear Views

    Those reluctant about digging into their radio to mount the DDS VFO P/C board, encoder (etc), may opt to build the whole thing in a separate enclosure as shown in the above pictures.  As you'll note, the prototype unit has 4 unmarked LED's across the top (VFO-A, VFO-B, SPLIT and LOCK), a red and a black push button, the tuning knob for the optical encoder itself, and the RIT control with an activation / deactivation switch.

    The rear panel shows the power connector, the VFO output and a third phono jack into which the transmit signal from the radio is to be plugged, as was done with the internal modification (R lead) that was just described.  

    The black button is multi-function to switch VFO's, operate split and lock the dial.  The red button is one press access to the split function.

    Note: The unit shown here worked very well with both my Ten-Tec Omni and Drake TR7.  Another ham is using it with his Corsair 1.

10. Over Voltage Protection

    Should the pass transistor fail on your power supply, the output voltage can quickly rise to 25 volts or so, wreaking havoc with your radio's solid state devices.  One way to guard against such a failure is placing a zener diode in the radio on the other side of the fuse so that of the voltage should rise above 14.8 volts, the zener will conduct and pop the fuse first.  I used a  1N6275AG purchased from Mouser and placed it in the circuit as shown here .

11. Installing an Integral Keyer

    The Jackson Harbor Press PK4 keyer has been installed in this radio.  Click here for the:
   I installed the PK4 on a 4-40 stand off just above the DDS VFO.  I used the 5 volt regulator on the DDS VFO to power the PK4, rather than connecting its small regulator to a 13 volt supply.  If you are going to do the same, don't install the small 5 volt regulator, but connect a jumper between its input and output.  Hold off on installing the PIC chip until you've made the following check.  
   Next item is the installation of  a 1/4 inch, 3 conductor jack for the keyer paddle.  The Ten-Tec 540 is a rather compact rig and - as such - I found it difficult to find a spot on the rear panel to mount the jack and a 100K keyer speed control potentiometer.  So, I removed the 540's headphone jack and replaced it with an 1/8th jack in a hole drilled close to the accessory socket on the rear panel (the headphone still cuts off the internal speaker).  I moved the mike jack up in the space normally occupied by the headphone jack (watch the fiber washers), and placed the new keyer jack in the bottom hole.  

    Once the keyer jack is mounted, you may connect the dit and dah leads and the keyer output wire.

    I decided not to mount the 100K speed control because I couldn't find a suitable spot on the rear panel and I didn't want to make any additional changes on the front panel.  This is not a significant problem because the keyer speed can be set with the memory push button and either the dit or dah paddle.  But - where to mount the memory push button switch???

    While the front panel (and the sub panel behind it) could both be drilled to accept a miniature jack (like the one previously installed), I decided to repurpose the Noise Blanker activation switch which is on the ALC control.  To do this, the lead to the S Meter lamp and its dropping resistor must be clipped from the switch, one side of the switch grounded and the other side run to the PK4 keyer board.  This location is adequate for infrequent controlling of the kleyer speed.

Note: If you would like to make full use of the PK4's feature (like the stored message capabilities), you might opt to 'bite the bullet' and mount a conventional push button on the front panel.

   The last connection interfaces the audio from the PK4 with the ten-tec audio amplifier.  I made this connection rather than  adding a piezo type speaker as it's more convenient.  The connection is made through a .01 mf capacitor to the INPUT pin of the Audio Power Amplifier board.

    When setting up the PK4 keyer (using the repurposed Noise Blanker switch and the paddles), be sure to DISABLE the SIDETONE from the PK4 and set the Side Tone Float.  This way, the Ten-Tec's sidetone will be used.  If you want to use the PK4's sidetone (I didn't try it because I've grown accustomed to the Ten-Tec's sidetone), then you'll have to somehow disable the Ten-tec's sidetone, etc.