Even during the busiest times of my life I have endeavored to maintain some
form of model building activity. This site has been created to help me chronicle
my journey through a lifelong involvement in model aviation, which
all began in Mayo, MD
you like re-visiting the old days of radio control (notice I didn't
use the adjective "good") to see how far we have come in terms of
equipment, then this article from the January/February 1963 edition
of American Modeler is just what you are looking for. Dr. Walter
Good (no relationship to the adjective mentioned above) developed
this "handheld" transmitter at a featherweight seven pounds to replace
his previous 32-pound monstrosity. Modern digital transmitters with
100,000x the processing capability
less than a pound. Being a tube circuit admirer, I have always been
impressed at what designers were able to do with so little. Some
day our kids will look back at the Futaba 14M (pic to the right)
and wonder how we managed to keep model sin the air with the need
to actually hold a transmitter at all (brain wave control will be
WAG - Hand-held Relayless Dual Transmitter
By Walter A. Good
was probably the jibes from my "friends" that caused me to develop
this handheld transmitter for the WAG Dual Proportional TTPW control
system. In particular, it was becoming very difficult to sign on
a contest mechanic because they all knew about my heavy 32 pound
transmitter with its old fashioned Y antenna! Now with a new hand-held
transmitter weighing only seven pounds, my friends are again more
helpful. It was certainly worth the effort to regain their confidence!
The handheld transmitter is not just a repackage of the
old dual system, it has several new features. Most important is
the elimination of the pulser relays. Besides the problems with
dirty relay contracts and bouncing relay contacts, I found it very
difficult to make a relay-pulser which did not have "lag" troubles.
This "lag" problem showed itself as a shift of the neutral position
when you tried to speed the pulser from four cps to ten cps. Or
worse yet, with the stick at one end you would get 20/80 and the
other end, 100/zero! The relay-less pulser cures this problem. And
no contacts to clean and adjust! As a result, "rate-buttons" have
been included in the transmitter to step the pulsing from four cps
to ten cps for additional functions.
Other features are
tiny center-reading meters permanently wired to the two pulsers
so the pulser operation can be easily monitored. Since there are
no clicking relays, monitors like the meters are necessary. No,
flying your plane in the fog by watching the pulser meters is not
recommended! Incidentally, the meters come from Lafayette Radio
as FM tuning meters with a rating of 50-0-50 microamperes at a price
tag of $2.95. They are the two small rectangular meters in the photograph.
The transmitter uses surplus nickel-cads and a DC/DC converter
for the power supply. The RF section has a low-power switch which
permits short range "distance" checks.
The handheld was
used for the entire 1961 flying season with good results. It was
on 53 mc and steered the Stink Bug with proportional ailerons, elevator
and three speed engine. Rudder control replaced ailerons in medium
engine speed and split drag-flaps were positioned down or up with
a long engine pulse. Maynard Hill's copy on 51 mc has also performed
well, especially on his 10 ft, dual proportional glider. His "fail
safe" worked on a motorized tow-release.
for larger version> Values for L1, 16T #22E-CTC 3/8"-Red
Slug, Tap at 4T; L2, 8T #16 - 1/2" ID - Air;
L3, 2T #16 - 3/4" ID - Close to L2.
for larger version> Overall chassis wiring shot.
Close-up of left side of chassis assembly & wiring.
Close-up of right side of chassis assembly.
for larger version> WAG transmitter timing diagram.
Probably the nicest feature was the self-contained aspect of the
handheld. No separate control box to forget, and even the 7-section
antenna is permanent. Its 8 1/2" slides almost completely into the
box when stored and then extends to 48 inches in use. It's European
and available from Polks in NYC.
Now let's look at the circuit
details of the transmitter. All together there are nine tubes. Two
each in the two pulsers, two in the tone oscillator, one for the
modulation amplifier, one in the RF crystal oscillator and one in
the RF doubler amplifier. The MOPA transmitter is exactly like the
old TTPW 50 mc version as described in the March 1957 AM. The circuit
diagram of Figure 1 shows the complete pulser-modulator, transmitter
and power supply.
The purpose of the TTPW (Two-Tone-Pulse-Width)
pulser is to generate a 100 cps tone with either 80/20 or 20/80
tone symmetry or a 500 cps tone with 80/20 or 20/80 tone symmetry.
Left rudder is 500 cps, right rudder is 100 cps. Up Elevator is
80/20 tone symmetry and down Elevator is 20/80 tone symmetry. Thus
the Rudder pulser pulses between 100 and 500 cps tones and the Elevator
pulser pulses between the 80/20 and the 20/80 symmetry. The engine
escapement is worked by a blip of carrier.
The tone oscillator
is a pentode multi-vibrator using two 3V4's, V-5 and V-6. The feedback
is between the screen grids and control grids through the .0015
capacitors C-8 and C-9. The 80/20 symmetry is generated by making
the grid resistors unbalanced. Note that R-35 is 2.2M and R-36 is
5.1M, hence V-5 will put out 20/80 symmetry and V-6 will put out
an 80/20 symmetry. Now all that is necessary to generate the Elevator
signal is to switch the output of the tone oscillator from the plate
of V-5 to the plate of V-6. This is done by the Elevator pulser.
Note that the only plate voltage for V-5 comes from the plate of
V-1 and the voltage for the V-6 plate comes from the plate of V-2.
When the Elevator pulser is operating, the plate voltage of V-1
(and hence V-5) will be about 10 V (V-1 conducting) and the plate
voltage of V-2 (and hence V-6) will be near 140 V (V-2 non-conducting).
The voltages reverse with every pulse. Thus V-5 first has high voltage
and then V-6. The two resistors, R-31 and R-34, mix these two outputs
together and C-11 sends them to V-7, the modulator amplifier, About
30 V peak-to-peak audio appears at the V-7 grid, so it operates
in a saturated mode and puts out a signal with over 100 V swing.
See Figure 2 for the waveforms. Only the 500 cps tone is shown here
to clarify the graph.
The tone oscillator will change frequency
if the grid return (junction of R-35 and R-36) voltage is changed.
This is done, by the Rudder pulser. The pulsing voltage from the
plate of V-3 varies from 10 V to 140 V and is applied to the grid
of the tone oscillator. When the V-3 plate is at 10 V, the tone
oscillator gives 100 cps and when the V-3 plate is 140 V, the tone
oscillator gives 500 cps. To obtain an accurate frequency value,
R-15 may be varied to set the 100 cps tone and R-28 to set the 500
cps tone. Figure 3 shows the tone change that would exist at the
plate of V-5 and V-6 if they were supplied with a steady B voltage
instead of the Elevator pulser voltage. When the symmetry and tone
changes of Figures 2 and 3 are combined and sent to the RF section,
the transmitted RF signal is shown in Fig. 4. In this example the
pulsers have different rates so we see all the combinations of tone
symmetry (20/80 and 80/20) and of tone frequency (100 and 500 cps).
Let's take a closer look at the pulser circuits. Since the
two pulsers are almost identical, we will discuss only the Elevator
pulser composed of tubes V-1 and V-2. Here again we have a multivibrator
with the feedback between the control grids and screen grids through
the 0.15 capacitors. The one megohm 60° control pot varies the pulse
width from 20/80 to 80/20 and results in the conventional pulse-proportional
response. The meter, M-1 (50-0-50 microamperes), between the screens
monitors the pulser action by accurately following the motion of
the control stick. At 50/50, it stands at the center and wiggles
at the pulse frequency. With the stick at either end, the meter
is at the corresponding maximum. The 470 K range resistor, R-5,
is selected to permit full meter movement. The pulse frequency is
varied from 4 cps to 10 cps by the setting of the pots, R-10 and
R-11. A switch, SW4, has been provided to quickly change the pulse
rate to operate a pulse rate circuit in the receiver. The resistor,
R-9, helps to keep the pulsing frequency constant independent of
the one meg control pot setting since most multi vibrators of this
type tend to speed up with the stick at either end. The pulsing
frequency should vary less than one cps for all positions of the
If you wish to stop the pulser in "up"
or "down" just apply a negative 45 V to one of the grids. This tube
becomes non-conducting and its mate becomes conducting. The result
is a steady output of the appropriate signal.
whole set of seven Pulsers-Modulator tubes have a plate current
drain of only 7 ma. at 140 V. Stable operation of the circuit was
found to exist over a range of plate voltage from 120 V to 180 V.
Note that all of the 3V4's are run on "half filaments" so each one
has a filament drain of 50 ma., or a 7-tube total of 350 ma. The
+140 V supply is obtained' by dropping down from 170 V and is filtered
by R-40 and C-7 (20 MFD) to prevent noise from the power supply
from interrupting the pulsers.
The modulation amplifier
presents about 100 volts of audio through C-12 (0.2 MFD) to the
grid of the 3B4 doubler. This is more than required to completely
cut off the 3B4 and gives close to 100% modulation. The switch,
SW3, is opened to remove the audio and permit the RF section of
the transmitter to emit only ,a carrier wave. The RF section draws
a peak plate current of 29 ma. during carrier only so the peak current
from the DC/DC converter is 36 ma. at 170 V. While pulsing, the
RF current drops and the total average plate current is 27 ma. SW6
introduces a 20 K resistor, R-45, and drops the RF plate supply
to about 40 V. This gives a low power signal and is excellent for
transmitter adjustment and receiver tuning at close range. The RF
filament drain is 430 ma. which, added to the pulsers, gives a total
filament load of 780 ma.
Toggle switch, SW1, turns
on the Pulser-Modulator and SW2 turns on the RF .section, In this.
way you can turn on the pulsers and show your friends the dancing
meters without emitting any RF signal.
of the handheld was determined by the position of the control stick
in the upper right hand corner of the box. This was found to be
an easy spot to hold the stick with the right hand while the box
is cradled on the left forearm. The fingers of the left hand reach
to buttons on the right hand end of the box. The batteries were
placed on the left end of the box so the weight would rest high
on the forearm. The six nickel-cads weigh about 3 1/2 pounds so
they constitute half the total weight.
As seen from
the photos, the Pulser-Mod deck carries seven tubes mounted below
the stick and the two-tube RF section is tucked into the space above
the batteries. The writer is indebted to West Coast DC/RC member
Bill Saks for the detailed layout and wiring of the Pulser deck
and RF deck. His neatness may be hard to duplicate but it is probably
responsible for the high reliability enjoyed with the transmitter.
The box is a standard aluminum one, 12" x: 7" x 4",
which has been thinned down to 12" x 7" x 3 1/4" by cutting 3/4"
from the mating halves. It was thought that 4" of depth would have
felt too awkward for easy control.
The finish on the
box was simple and very attractive. After cutting and drilling all
of the holes, the outside of the box is "buffed" on a belt sander
giving it a scratched finish. Then a 10 minute anodize hardens the
surface and gives it a satin luster. The hot sun reflects nicely
from this surface so the transmitter stays quite cool. One point
of caution: the aluminum can easily be eaten away by the potassium
hydroxide from the nickel-cads. A coat of clear dope around the
battery area seems to help. The cells I used had rubber sleeves
at the top. The sleeves were pierced with a needle so that the pressure
during charging would not build up so high and splatter electrolyte
Access holes are made in the back cover for
the RF-Hi-Lo switch and to observe fluid level in the cells. Another
hole is placed ·above the RF capacitor, C-19, so the final amplifier
may be peaked with the case in place. This hole is protected with
a rubber, grommet since there's a 170 V on the capacitor shaft and
you may want to tune with a metal screwdriver !
control stick uses two 60° one meg pots·and they are mounted similar
to those in the ACE kit. The "scissors-type" centering spring has
been added to each pot shaft to give a snappy center return. It
has been found that better proportional flying is possible if the
rudder pot can be moved individually without moving the elevator
pot and vice versa. Hence the desire for separate centering. The
photo shows the compactness of the control stick and pot assembly.
The antenna is mounted on a piece of 1/16" epoxy-glass
board in the corner of the box so that it remains in the main box
when the rear cover is removed. The corner of the cover is trimmed
off to miss the antenna support.
DC/DC converter (6 V to 170 V) is mounted between the batteries
and the end of the box. One of the Diem units (Model # 518 gives
170 V at 29 ma.) has been used in this spot. The converter uses
five nickel-cads (6 V) and the remaining cell powers the filaments.
The filament cell positive is grounded and the negative is led to
the filament switch. This reversal from normal practice permits
the six cells to be charged in series. The seven-pin socket just
above the converter is not shown in the circuit diagram but it connects
to all six cells. A separate meter plugs into it to monitor each
cell voltage after the flying session. The same meter monitors the
cell voltage during the charging period.
carrying handle which was lifted from an old Heathkit and is mounted
quite a bit off center. Actually, it is right over the c.g. of the
box and hence the carrying level is horizontal.
experience with the handheld transmitter has been very good. No
crashes have been attributed to a malfunction of it! We have other
good alibis for our crashes! On one occasion, I tried to fly, unknowingly,
on low power RF and didn't realize it until the plane started kicking
"up" and "right" about 600 feet away. Quickly flipped to high power
and the plane straightened out. Another time, one nickel-cad in
the transmitter went dead but the plane kept on working.
There have been occasional kicks of the plane controls indicating
the passing through of a signal null. Almost every time this happened
one of the following conditions has been present:
1. Receiver was off tune and needed re-tuning.
I was standing in line with several tall ground-based antennas which
were blocking the signal in one direction.
from reinforced concrete runways which seem to give a. sharp reflection
and a consequent momentary null.
None of these kicks
was catastrophic but they don't look good in the middle of a procedure
Although in the past I've always worked to keep
the Rudder and Elevator pulse frequencies well separated, I was
surprised to find the best operation for this transmitter was when
they were made the same. Thus, I find that both Rudder and Elevator
are being pulsed at 4 cps. This holds well for the all stick positions
out to half deflection. From there out the frequencies are slightly
different but no serious "beating" or interaction takes place. On
the ground the interaction between the controls is noticeable at
10 cps but in the air it is not possible to see the plane react
when switching either Rudder or Elevator from 4 cps to 10 cps or
back. The next project is to put some rate detectors in the plane
to use these rate changes. The Dual system would then give two proportional
controls, engine escapement and two on-off controls.
In tuning the pulsers the meters give the best indication. Just
center the control stick pot to center the meter. The stick should
have enough freedom of motion for the meter to indicate its maximum
reading just before the stick hits the edge of its hole. The wiggle
of the meter may be damped by placing a 100 MFD, 6 V electrolytic
across it. This has been tried and worked for several months, but
since the voltage on the meter has both polarities, one of the capacitors
went bad and shorted out the meter. These capacitors have now been
The tones may be set by removing tube V-1
to stop the symmetry pulsing and then removing tube V -4 which leaves
only the low tone. Now adjust pot R-15 to give 100 cps using an
audio oscillator as a reference. To set the 500 cps tone, replace
V-4, remove V-3 and adjust R-28. These controls interact slightly
so it may be necessary to do this several times to obtain an accurate
setting. Once set, the tones should hold very well.
The RF section is checked out first on low power with the pulsers
off. Tune L-1 until a monitor receiver indicates that the crystal
is oscillating; also a downward jump in M-3 will take place. It
has been found that the 50 mc transmitter requires a very active
crystal. Both ACE and International crystal units have worked well.
Then tune C-19 until a nearby field strength meter (FSM) gives a
maximum reading. Re-tune L-1 until it is about 1/4 turn from where
the oscillations cease. Now try L-3 antenna coil closer to L-2 and
re-tune C-19. Try different spacings until you obtain the best FSM
reading with the. smallest RF amplifier plate current on M-3. All
of the foregoing may be done with the back cover removed. Before
attaching the cover, switch to high power and place the FSM some
distance away; 12 ft. is just right for mine. And check tuning of
L-1 and C-19 .for the best output but leaving L-1 on the safe side.
Put the cover in place and make one final touch up of C-19. Flip
on the pulsing and the FSM should drop to about half. Moving the
Elevator stick should cause a variation in FS while the Rudder should
not. Now she's ready to go to the field!
always some improvements that could be made in a new device. I expect
the six 9 1/2 oz. (3/4" x 2 5/8" x 4 1/2") plastic nickel-cads I
used could be replaced with a smaller sealed type. The 9 1/2 oz.
type were rated at 5AH and give almost four hours of safe flying
on a full charge since the current .from the 6 V supply is 1.1 amp.
Probably a size-D sealed cell of the 4AH sintered type would give
well over three hours. They would also take less space and lighten
the transmitter considerably. Some of the 6 oz plastic types would
also be suitable.
A little more RF power than the
present 1/2 watt would be desirable. One way to get more radiation
would be to use a "loaded" antenna with a loading coil in the center.
I gave this a quick try using the Graupner antenna, but came up
with no improvement on the FS meter. Just why I don't know, but
it should help. Another help would be a "straight-through" amplifier
of 50% efficiency instead of the doubler with its 25% efficiency.
Look at the MAC 50 for ideas on this (ATMA, 1961).
The possibility of a trim control on both the Rudder and Elevator
would be handy. Right now this must be done by mechanically shifting
the pot relative to the stick, and of course, only between flights.
In-flight trim would be more desirable, especially with a new plane.
The handheld has not been tried on 27 mc as yet. There is
reason why it won't work just as well there.
has not been a constructional article, it is hoped that some of
the ideas and circuits will be useful to the large family of proportional
The list of parts required for the transmitter