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
to your radio incurred as a result
of your reading this website.
Dual VFO, Digital Display and Internal Keyer for Your Ten-Tec Triton 540
- Other Triton
Information / Modifications
Manuals and Miscellaneous Information
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
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
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 -
For the DDS VFO itself, you'll need about $60 - less if you have
a well stocked junkbox. The most
expensive part is the
encoder. I found nice ones on
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 schematic, the P/C
board 2 artwork,
the wire connection points and a completed
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
possibly find a used external Ten-Tec digital display, I decided to
mount an Almost All Digital Electronics
device within the radio and on the front panel (more later).
a) Disassembling the
- Remove the top, bottom
and side covers. On the bottom
you'll note that the speaker connection coax is rather short
and has not been provided with a quick disconnect
plug. To save a lot of frustration and possible
just unsolder the wires at the speakers.
- Before you
start the modification, ensure that your radio is working. If you have received your Triton without
the octal plug in the rear panel, strap 4 and 5
together, and pins 6, 7 and 8 together, enabling
the PTO. If necessary, apply deoxit (or equivalent) to the
bandswitch contacts / switches / controls and rotate them back and forth several times. This will make a big, long term improvement.
- Also, you might check the bandswitch soldered joints on the
Mixer boad as some might have become
intermittent (due to the torque) For most contacts, one can usually see
the intermittent which looks like a slight crack in the silver colored
solder with a sliver of bright copper underneath, these may be
repaired with a fine tipped soldering iron.
- Finally, you may also want to check the alignment,
especially the TX-RX Mixers and the SSB Generator frequencies to ensure that the USB / LSB /
CW oscillators are where they should be relative to the 9 Mhz 8 pole crystal
filter. This requires a dummy load and a scope, and is easily
done. My 540 was 'off' a bit and this affected the
quality of received SSB transmissions. This will be important
when adjusting the DFD1A.
all the knobs. The
bandswitch requires a small slotted screwdriver. Some of the remaining
knobs (like the PTO tuning) require a very small (.05)
wrench - others just pull off.
- Remove the 2 bottom screws holding the
slide the panel forward, unplugging the small connector that provides
to the OT and the ALC lamps. Set this panel aside.
- Remove and discard the dial cord, the pointer and anything
else associated with the slide rule tuning mechanism.
b) Removing the PTO
the two front panel screws holding the PTO in place. Remove
side screws (may
require the temporary removal of a circuit
- Unsolder the 4 wires from the PTO
(white, green, orange and brown). Remove the PTO
from the radio. The green,
orange and brown wires connected to the P/C board are removed.
The white wires remain as they will be connected to
the output of the DDS VFO (described later).
c) Pretesting and Mounting
the crystal calibrator, making room
for the DFD1A
circuit board. If
you decide to remove both sockets, reconnect
the 2.2K resistor between
the white and green leads as it is required in the
The violet wire will be used later with the DFD1A.
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
a counter, your station receiver will suffice. You can even
connect it directly to your Triton at the rear jack provided for a
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
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
peak to peak. If you
have a 'scope, use it to set the DDS VFO's board right on the
just turn R5 slowly until the radio begins
to receive properly on all
bands, but no higher.
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
of perf board between the DDS VFO board and the chassis to eliminate
the possibility of any short circuits. I also installed a
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
If you monitor the signal on your receiver, you'll hear a
rough, warbling note. This is normal as the
OFFSET / RIT
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.
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
for the 4 offset leads and the transmit lead going to the R lead on the
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.
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
Using a 4-40 screw, you can 're-tap' the existing
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
VFO - through the small hole in the VFO enclosure - to the new terminal
strip and terminate the shield to ground. The 2 white leads
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
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
(I used a scrap of double sided P/C board) and
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.
- there are four (4) connections for the
optical encoder - +5VDC, ground and the two phase (Phase A and Phase B) connections,
as shown here.
- using your voltmeter, double-check both the +5VDC and
ground connections on the controller board. They are located on JP-4.
The connection at the TOP
and the one at the BOTTOM
both connections. Run the wires through the small hole in the VFO
enclosure and tie them to a spare lug
on the previously installed terminal strip.
e) RIT / OFFSET
- connect the remaining 2 phase leads to the remaining
pins, power up the radio and turn the encoder. After you've
installed the digital display you'll know if the DDS
VFO is tuning in the right direction. You've a
50 / 50 chance on being right the first time.
Note how the tuning acceleration algorithm works. Unlike
the PTO, one can get to either band edge in a hurry.
If you would like to verify its operation before the digital display
has been installed, just connect a frequency counter to its output.
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.
- Remove the Control Board
and its paper insulator. Take
note of its orientation so that it may be properly reinstalled.
- Remove the adjacent SSB Generator
and the TX-RX
Mixer boards, setting them and their insulators in a safe
- Note the wiring on the Offset board connector.
There should be
a bundle of 4 wires (brown, white, violet and gray, brown) that run from the Offset control.
and violet leads are connected to the Offset potentiometer, and
the gray wire disables the OFFSET.
- Carefully remove these 4 wires
from their lugs on the Control board and move the whole wire forum
so that you can reinstall the Control Board
and the SSB
any other wires.
- Push these wires through the previously drilled grommeted
hole for subsequent connection to the DDS VFO board.
- Examine the wiring bundle from the Offset control and note
the yellow wire and where it is
on the underside of the TX-RX Mixer board.
This wire goes to the T lead
and its purpose is to disable the OFFSET when the radio is in the
transmit mode and to switch the VFO's while in the SPLIT mode. Carefully remove it from its connection on the
Mixer board and connect it to a nearby ground lug
(as shown here).
- Place your meter on the gray wire and verify that it goes
to ground when the OFFSET
is disabled (control pushed in). It's
very important that the proper yellow wire is moved as the T lead
voltage will destroy the processor chip.
the DDS VFO board, connect the while wire to the RIT CTR, the brown
wire to RIT 5V, the violet wire to RIT GND, and the grey wire to RIT DISABLE, as
Installing the Digital Display Controller - Repurposing the Crystal Calibrator
the TMIT on the DDS VFO board to the R lead on the Control Board and replace the insulator and then the TX-RX
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
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
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
to these points after the
board has been mounted on the perf board. I used wire
straps to hold it in place.
makes for an exceptional digital frequency readout. However,
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,
opted to use (repurpose) the existing push / pull switch on the RF gain
the one that was used to activate the crystal calibrator.
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
has a 12
VDC tie point (4 wires) on one lug,
and a voilet wire on the other. This is the violet wire that
to the previously removed crystal calibrator board. The
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
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
the narrow space between the chassis and the front panel.
carefully measuring and drilling the holes, I mounted the display with
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
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
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.
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
g) Reworking the Front Panel
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
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
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
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
- turn the radio on again and note the
digital display. It should show a frequency close to the low
end of the band. Then turn it off again.
- Turn the
radio on and vary the OFFSET / RIT
control (pull it out), ensuring that it works in the proper direction.
- Verify that the FUNCTION
button - when briefly tapped
- will switch from one VFO to the other.
that the radio transmits properly in the SPLIT
- Complete the alignment of the DFD1A
by adjusting the top mounted resistive trimmer.
When powered up, both the A and the B
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.
the RIT (OFFSET) switch is activated (pulled out), the receive frequency will vary
its setting; the transmit frequency will not change. When
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
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
twice (a short followed
by a longer tap - like a
' A' in CW) and the radio will enter the
SPLIT mode. The on-line
will control reception, while the off-line VFO will control
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
VFO will be copied into the off-line VFO.
LOCK the system at any point, just hold the FUNCTION
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
Note: if you have wired up
the optional LEDS, the LOCK LED will be illuminated.
has been added dedicated
to the SPLIT
it one time and the SPLIT
function is active. You can then
the main button to switch between the VFO's. Tapping the
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,
the button and push it again within
If you have equipped the LED's, they will all flash 3 times
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
5. How the Software Works
30,000 Foot View - click here
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.
Meters - 3684 khz, 3888 khz, 3950 khz, 4000 khz
Meters - 7143
Meters - 14190
Meters - 21111 khz, 21320* khz.
Meters (A) -
28086 khz, 28143khz, 28272hz, 28333 khz, 21484 khz
Meters (B) - 28919 khz, 28975 khz*
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.
Meters (C) -29083
To be determined............
8. Other Concerns /
If the user decides to tune up the
antenna to make
(say, answering a CQ), and if the antenna SWR is too high - the power
supply circuit breaker could trip. Since the DDS board is
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.
9. Using an External DDS VFO Controller
- Front, Side, Rear Views
- 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.
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
tripping would not cut the power to the DDS VFO module.
- Alternately, the operator may gradually increase output
power (using the drive control) when tuning up to an antenna.
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-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
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.
- Connect the 5 vdc lead up and verify the presence of 5 VDC on pin
1 of the PIC keyer socket.
- If 5 VDC is present where it should
be, then go ahead and install the PIC processor.
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.
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.