Display for Heathkit SB, HW, HR
Drake 2A / 2B / 2C Radios
(New Boards Sold Out - 2/18/18 - Contact Me If You Would Like Me to Order More)
Neil Hecht founded the Almost All Digital Equipment (AADE) enterprise
produced many innovative electronic adjuncts for radio amateurs.
Unfortunately, Neil passed away last year and the status of
excellent product line is uncertain at this point. You are
encouraged to view his preserved site on the internet Wayback Machine.
Inasmuch as I
had built several of his DFD2 units and found them quite well done, I
was disappointed that I could not order another unit.
So, I replicated his
custom DFD-2 for the Heathkit SB line, for the HW radios, for the
solid state HR-1680, and for the Drake 2 series. This project
has been designed for the experienced homebrewer.
will make the bare-bones boards and pre-programmed PIC processors
others who might like to build one up. I will not have the
to coach anyone through the building process nor assist with the
installation within any particular radio. For this, you
probably refer Neil's website on the Wayback Machine.
You'll notice in the picture that this particular display has been
installed in a very large enclosure, mainly because I wanted to use a
large, 1x16, one line display. Since the P/C
board itself is just
2.5 by 4 inches, it may be readily mounted in a smaller enclosure
(providing a smaller LCD
is used). The LCD itself can be 'wired'
to plug directly into the P/C board, or connected to the board by
either a ribbon cable or individual 30 gauge wires - your choice!
and Schematic -
Phase 3 Board
My P/C board design
is very similar to the one
that Neil developed except that:
How It Works - Phase 2 Design - Either 100 Hz (Faster) or 10Hz (Slower)
Frequency Accuracy (Read Below) May be Selected
is 2.1" by 3.2,
- there is no ground plane,
- the 2 variable resistors used to set the offset and the
TCXO trimmer have been omitted,
- either a 'canned' oscillator or a mechanically trimmed TCXO
can be used, the
mounting holes have been provided should the user desire to mount the
unit against the chassis and wire the display separately, and
- the software was developed in-house.........
For the Heathkit and other similar transceivers, the software first
reads and stores the HFO and BFO values, subtracting the BFO from the
HFO and placing the result in a holding register. This value
updated every 2 or 3 seconds. Then the VFO is
sampled and subtracted from the holding register.
Two versions of the
program will reside on the same
PIC16F628A. The original program can be accessed by
leaving the strap OFF the SPARE pins. This program
will check the
frequency between 3 to 4 times a seconds and will provide a 10 Hz
readout. A faster version is available by strapping the SPARE
pins. This program will make 10 samples per second and
100 Hz readout, and is more suited for rapid QSY activity.
You can check them both out to see which better suits your
application and preference. Just be sure to power down the
making the changes or the display may not be correct. If
you want to cycle between the two program versions, you could
install a miniature SPST switch somewhere on the enclosure.
Note: In either version, the LCD is updated only when the
frequency changes, thus eliminating the repetitive 'chirps'.
If you are building this board, you
first have to determine if you want
to mount the LCD display directly to the P/C board, or just mount the
P/C board on the chassis and then use either 30 gauge wire or ribbon
cable to interconnect the
two. You also have to decide upon a suitable enclosure if the
display is to be mounted externally.
If you plan to mount
the LCD on the P/C board, then the TEST
wire pins must be mounted on the foil side of the board along with R8
(the LCD contrast adjustment).
populating the P/C board, it's vital that the components be installed
on the proper side as you'll pay hell to remove them if they have
been incorrectly installed on this board which has neither a component
or solder mask.
Some back lit LCD displays may be powered
directly from the on-board LM78L05 regulator by selecting a suitable
dropping resistor (R10). The voltage drop
across the LEDs is usually 4VDC, with the current ranging
from 20ma to 150ma. The
required is R = (V-4)/I where I is the desired current and V is the
supply voltage. If the
backlight on your LCD will not draw more than 30 ma, then you may use
display board's LM78L05 regulator. I
used a 47 ohm resistor on mine which drew just 12 ma and provided adequate brightness.
Important Note: If
your LCD display draws more current and the
LM78L05 gets very hot, then power both the board and the display with
LM7805 heat sinked to the chassis of the radio to which the
digital display will be connected.
- Install the 16 pin socket
for the HFO, VFO and BFO (all CD74HC4046).
be sure that the notches point towards the inside of the P/C board.
if building a DFD-2 board for the Drake 2 series radios, you may omit
all the shown BFO connections as the BFO is not used in this design.
- Install the 16 pin socket for
the CD74HC153 with the notch
pointing toward the bottom of the board.
- Install the 18 pin socket for
microprocessor with the notch
pointing toward the bottom of the board.
the (7) .1mf ceramic capacitors.
- Install C4, C5 and C6 - all .01 mf capacitors,
- Install the (6) 1N4148 input protection clamping diodes for
the HFO, VFO and BFO (if required),
- Install R4 (100 ohms), R2 (1K ohms) and R5 (1K ohms).
- Install R1, R6 and R9 - all 10 K resistors.
- Install the reversal protective diode D7,
capacitor C1 and 5 volt voltage regulator U1,
- Install the 2 pin jacks for the 13VDC power and the HFO,
VFO and BFO outputs.
- Install the 2 pin TEST jack and the SPARE jack.
- Install the 16 pin header for the LCD.
need NOT install PICKIT3 or R7. These
connections are for
my own use (in circuit programming on assembled boards).
- Install the 10K LCD contrast control (R8).
- Install the 4 pin 'canned' crystal oscillator (Mouser -
This is a 4 pin DIP and it must be properly
though the package has three spacers on the botom to avoid shorting out
any traces underneath it, you might consider mounting it slightly above
the board Pin #1 of the oscillator has a pointed edge.
are some pictures showing how to orient the package before soldering it
- If you are installing an adjustable TCXO, place some solder globs on the proper pins, as shown here.
- Connect the LCD display. I used 30 gauge wire wrapped wire
from eBay. It's quite convenient and flexible.
- Apply 13 VDC power to the power connection and
verify that +5 VDC is present on pin 14 of the microprocessor, on pins
15 and 16 of the CD74HC153, and on pins 16 and 3 of the CD74HC4046.
- Remove the power and verify that ground is present on pin 5
the microprocessor, on pins 1, 8, 10, 11, 12, 13 of the CD 74HC153, and
on pin 8 of the CD74HC4046 sockets.
- Determine the value of R10 to be used for the LCD
convenience, this resistor can be mounted on the P/C board, proper.
- Install the integrated circuits.
6. Enclosure Suggestions
- If using a 1X16 LCD, jumper the LCD pins. If
using a 2 line LCD, leave the LCD jumper out.
One of the few worthwhile
items one was once able to find at Radio Shack is a good plastic
enclosure. I used the smallest I could
find (5 x 2.5 x 2 inches) that would hold
electronics which is stock number 270-1803 ($5.49). The
boxes is easily cut
with an Exacto
(or similar) knife, and some may be available from eBay scalpers.. Some suggestions:
- connect the board to the LCD (using 30 gauge wire) and then
test the complete assembly,
- cut a hole for the LCD in the lid and mount the
- mount the board in the rear of the box leaving space for
the interface and power cables,
- drill small holes for the interface cables and connect them
to the PCB.
Using 2 to 3 foot lengths of RG-174 (or
PHONO plugs on one end and and solder the other end to the HFO, VFO and
P/C board connection points. Either tag or color code these
connections and insert them into the SB-300, SB-301, SB-303, SB-310,
(etc) radio of your choice and the appropriate jacks will have already
been placed on the radio's rear panel. These are the easiest interfaces.
Some minor additional work will be required for the HW-100,
HW-101, SB-100, SB-101, SB-102 (see below), and to the HR-1680.
may need to repeak
the heterodyne oscillator
the additional capacity may detune
If you are mounting the
circuit board on your radio's chassis, ground each of the 3
mounting holes by soldering a small
gauge wire from them to the ground that 'runs' around the side of the
board. Use spacers so
that the board does not
- All connections are made at the cathodes of the various
connections are made through a 27pF cap and RG-174 coax. 27
was found to provide adequate coupling without loading any stage.
- HFO connection at pin 7 of V11
- VFO connection at pin 7 of V12
- BFO connection at pin 9 of V13
- Bypass (Jumper out) the input .01 and the 1 K resistor on
the HFO input circuit of the counter if it will not count above 15
- Keep cables as short as possible.
As in the case of the Heathkit SB / HW
series, connections are required to the HFO, VFO and BFO
points within the radio. These connections - made with
coax (RG-174 or equivalent) - are sent through a small capacitor (from
30 to 60 pf). The HFO and VFO
connections are made on the underside of the
chassis, whereas the BFO
connection is made on the AUD / REG circuit board (D). The
connection is made at the top of the board with the shield of the
coaxial cable terminated on the rear of the board.
making the BFO connection, be sure to leave enough coax so that the AUD
/ REG circuit board may be placed on an extender should service ever be
Suitable RCA phono jacks are mounted on the radio's rear panel where
there is also a convenient source of 13 VDC. Radio Shack
suitable connector (#2740222).
Connections to the SB-300 / 301 / 303 are very simple as Heathkit
designed these radios with suitable pick-up coils on the Heterodyne
Oscillator specifically to send the HFO signals to a matching
transmitter. With them, it's just plug 'n play'.
Connections to the SB - 100 / 102 / 102 and to the HW-100 / 101
are a bit more involved in that the HFO, VFO and BFO signals can be
picked off the cathodes of the respective tubes. The
HR-1680 conversion may be a bit more involved, especially if operation
on 15 and 10 meters is contemplated. While the display will work
with direct connection (via a small capacitor) to the HFO output, the
additional capacity on these overtone crystals may attenuate the HFO
output and the received signals.
To solve this problem, a small 2N3904 emitter follower circuit is mounted it under the chassis (on double sided tape), as shown here.
With it, received signals are significantly improved on the higher frequencies.
Also Note: This is the same circuit as the HFO buffer used in the Kenwood TS-520 radios and also displayed on the inactive AADE website. It works!
10. Drake 2 Series Radios - see schematic
If you are building your own board, please follow the instructions shown here.
The same DFD-2 Interface Board (but with a different program) can be used to provide digital dial display capabilities.
The BFO input is not used in this conversion. Connections are
made from the DFD-2 board - using RG-174 miniature coaxial cable - to
the Drake's Heterodyne Oscillator (HFO) and to the Drake VFO circuit.
As in the case of the HR-1680, a simple buffer circuit (shown on the schematic) needs to be constructed so that the HFO
signal will have sufficient amplitude to drive the DFD-2 circuit.
Those who don't regard their unmodified Drake 2B as a potential
priceless heirloom may decide to install 2 RCA Phono jacks on the rear
panel. Others may decide to run the coaxial connections through
the existing rear chassis ventilation holes. Here are the connection
points along with some pictures:
- The HFO buffer (emitter follower) circuit is constructed on a small piece of Me Squares from QRPME.com,
and then epoxied between the tuning coils on the side of the radio (as
shown). The input side of the HFO buffer is connected to the
cathode (pin 8) of V2, the crystal oscillator tube (6U8A). This is the same circuit as the HFO buffer used in the Kenwood TS-520 radios and also displayed on the inactive AADE website. It works, even at 7.7 volts DC (rectified and filtered filament voltage).
VFO connection is made - through a 20 pf capacitor - to the cathode
(pin 2) of V3, the VFO and second mixer tube (6BE6) - with the coax
shield connected to a ground point.
When I originally coded the PIC, I set it up so that it would
automatically detect the XTAL HFO frequency and 'know' when to either
add or subtract the VFO. However, because Drake slyly decided to
use a single 25 Mhz crystal for 21 / 28.5 Mhz (15 and 10 A meters), a
switch was needed whenever the 25 Mhz crystal was selected. Now,
since an outboard switch was necessary, I decided to let the user
decide whether to add or subtract the VFO on any band. This way
any crystal can be used that is permitted within the preselector's
tuning range. It's easier said than done., e.g.:
- Drake 2 C Conversion: -
I don't have a 2C, but have included the service manual. The
HFO will be picked off the solid state HFO (don't know if a buffer
board will be required), and the VFO connection made - as in the 2B -
off pin 2 of the VFO and second mixer tube.
- In the DOWN
position - 80, 40, 20 and 15 meters are enabled.
The display will work in 2 modes - SLOW and FAST.
- In the UP
position - all of 10 meters (if your radio has the appropriate crystals).
- The SLOW mode provides an accurate 10 hz display, and the display is updated about 4 times per second.
- The FAST mode offers a 100 hz readout, but is updated much more quickly and is ideal for rapid QSY operation. To select the FAST mode, jumper the FAST pins.
To ensure 'spot on' accuracy, ensure that your radio is aligned
properly. Pay particular attention to the 50 and 405 khz
oscillators. Get them right and you'll be rewarded by exceptional display accuracy. Align the radio when it's been on for an hour or so. My Drake's 405 khz oscillator will drift a bit after it's first turned on - Your mileage may vary. Any drifting has to do with the 2B / 2C itself - not with the display which is clocked by a TCXO.
Drake 2B 'Birdies' - Insignificant
You may notice some low level birdies here and there as you tune across
the bands if the radio is out of its cabinet and if no antenna is
connected. Some of these are entering the radio via the front end
circuitry as they become stronger as the preselector is peaked.
However, with the radio placed back in the chassis,
and with an antenna connector almost all - except for one on 10 meters
- are obliterated. In this regard, the Drake DFD-2 application is
cleaner than some of the others I've tried.
The digital display needs a permanent source of 13 VDC power.
This can be accomplished by using an appropriate wall-wart,
deriving the power from the radio itself. If the radio is
by a 13 VDC source (like
the SB-303 or the HR-1680), then a suitable
power source can be found within the radio. If you
power the display from a tube type radio, then you'll have to derive
the power from the filament circuit by using a simple voltage doubler
rectifier combination (google it).
Once you have verified that the proper voltages
are present on the IC's, you may install the integrated circuits and
make the connections to the LCD. Connect the digital display to your
radio and apply power. Adjust R8 for the proper contrast.
Switch on your radio and verify that some frequency is being
CAUTION - - CAUTION - - CAUTION
- when applying power to the board, please be sure that you use the
proper pins (lower left hand corner). If you connect power to the
wrong pin, you'll destroy the MP, the TCXO (if used), and possibly some
If you are using the 'canned' oscillator (Mouser - MXO45HS-3C-20M0000),
calibration is required. It should be smack on.
verify this, (for heathkit programmed DFD-2's) you might want to place a temporary jumper across the TEST
pins which will make the DFD-2 work as a general purpose frequency
counter up to 50 Mhz, or thereabouts. The HFO input will record the frequency to which
lead has been connected - for example - the crystal
If you opt to use a mechanically
adjustable TCXO (wired
with 30 gauge wire the the canned oscillator's connection points),
connect the output of the HFO to the oscillator's output and adjust the
display for 20 Mhz - or just monitor it on a very accurate receiver.
the TCXO's that I pirchased on eBay and installed on pre-assembled
boards did not require any tweaking - they were apparently set at the
factory. I did notice - however - that their accuracy was off a
bit after they were soldered inton the circuit. Allowing them to
properly cool solved this problem. After all, they are temperature compensated, right :-)
Most every radio equipped with a digital frequency display has its
share of internally generated 'birdies'. Anyone who has used
like the Ten-Tec Digital Century 21, the Ten-Tec Omni series or even
the Drake TR-7 will confirm this phenomenon. Therefore, it should come
as no surprise that the DFD-2 Clone will generate some low level
'birdies' - here and there. In most cases though, normal band
atmospheric noise will render them largely unnoticeable.
a) SB-300 Series
There are some
very minor 'birdies' that I noticed on my SB-300. Whether or
will appear on your radio is anyone's guess. Normal band
should mask them out, and grounding the P/C board directly to your
radio's chassis will further attenuate them (none caused the S
meter to 'twitch'):
- 80 meters - 3649, 3700, 3734, 3866, 3903
- 40 meters - none
- 20 meters - 14032, 14198, 14212, 14239
- 15 meters - 21050, 21197, 21371, 21403,
- 10 meters (A) - 28077, 28397, 28456
- 10 meters (B) - 28502, 28749, 28814, 28895
- 10 meters (C) - 29049, 29134, 29323, 29400
- 10 meters (D) - 29510, 29699.
The unmodified radio - with no antenna connected - will exhibit
'birdies' that are strong enough to move the S Meter at 3652 Khz, 3738
Khz, 7030 Khz and at 21200 Khz.
13. YAESU FT-101
- Software Not
1) You may use the remote VFO plug (octal) if:
- You are sure that you, or anyone else will never
want to install a Yaesu remote VFO;
- You have a spare octal, male plug;
- You are willing to work in a very restricted space.
2) You may bring cables out of the rear of the rig
and terminate them with RCA or
BNC connectors at the Digital Frequency Display unit if:
- You are not concerned with affecting the resale value of
the FT-101 by drilling
holes in the rear panel;
- You want to avoid soldering to an octal plug in a very
3) You may install RCA or BNC chassis mount jacks on
the rear panel if:
- You want the modification to appear as inconspicuous as
- You don’t want cables that cannot be disconnected at the
- You are willing to very accurately measure and drill
mounting holes in a very
Yaesu FT-101 Signals
The BFO signal (3.1793 MHz) is
approximately a 3 volt
(peak-to-peak) signal that may be
tapped in either of two different places. It appears on pin 6
of board 1184A and is
carried by a short piece of coaxial cable to pin 5 of board
1183A. Each board has a
convenient grounded pin for shield connection, but board 1183A is
easier to reach with a
small soldering iron.
After routing the new cable (or
mini-coax, which ever you have
chosen) from the rear
panel to the area of the board chosen, solder a .01
disk ceramic capacitor to
the center conductor of the cable. Then solder the free lead
of the capacitor to the
chosen pin of the board edge connector and the shield to the nearest
grounded pin on the
The Local Oscillator signal
(approximately 6MHz above the
displayed signal, or 8 to 36
MHz) is approximately a 3 volt (peak-to-peak) signal that is available
at the test point
near the top edge of board 1181A.
You have 2 cabling options
here. The first option is
to route the cable from the
rear panel toward the front of the transceiver, and the openings around
dial. Use these openings to pass the cable to the top of the
viewing the FT-101 from the normal operating position in front of the
rig, route this
cable up over the tuning shaft and to the right of the
chassis. Solder a .01 disk
ceramic capacitor to the center conductor and a small ground lug to the
Solder the free lead of the capacitor to the test point at the top of
and attach the ground lug under the adjacent control’s mounting nut and
CAUTION. This method of installation means that you must
disconnect the ground lug in
order to remove the board from its edge connector.
AN ALTERNATIVE installation method is to install the blocking
capacitor (.01 disk
ceramic) on the board between the test point and unused pin
15. This will allow easy
removal of board 1181A. However, it
requires soldering the coax to the
edge connector for board 1181A in a very congested area. In
installation the cable stays on the underside of the chassis and is
soldered to pin 15,
with the shield is soldered to pin 18 of the edge connector for board
The VFO signal (approximately 9 MHz) is about a 1 volt
(peak-to-peak) signal available
at pin 11 of board 1180A. After routing the cable from the
rear of the chassis,
solder a .01 disk ceramic capacitor to the center conductor.
Solder the free
capacitor lead to pin 11 and the shield to pin 10 of board 1180A.
(The VFO signal also appears on the remote VFO adapter (octal)
plug. In the beta
unit this signal appeared to be a little dirty causing erratic
operation until the unit
had warmed up for awhile. This may be peculiar to that one unit.)
2016, 2018 K3JLS - All Rights Reserved - Software Included