Trans-Ind, the Aircraft Comm. Transmit Indicator
A product from Electrical Efficiency Systems
Product Description
Engine performance is monitored with temperature and pressure gauges, and tachometers to let you
know immediately when there is a problem that could result in engine failure. The sooner a problem is
noted, the more time and options there are to deal with it. Likewise, continuously monitoring your
radio transmitter performance allows more time and options to handle communications radio problems.
Trans-Ind (Transmit Indicator) monitors your communications transmitter every time you push the
transmit button and lets you know that you are putting out radio waves as well as voice.
The two full-sun visible LED indicators, carrier and voice, provide a clear indication of the most
common aircraft transmitter problems: stuck transmit buttons and incorrect or inoperative microphone
connections.
Trans-Ind is battery powered, with a battery life of about 100 hours. The instrument mounts to the top
of the instrument panel with velcro strips that are included. The unit does not emit any radio waves and
will not interfere with existing radios.
How it Works
Trans-Ind is a broadband radio frequency detector. The unit detects the entire aircraft communications
band, 118 to 137 MHz. There is no oscillator or mixer that can interfere with your existing aircraft
radios.
Trans-Ind indicates the actual radiation energy, it does not matter which nearby transmitter is operating
or why it is operating. If the 121.5 MHz ELT (Emergency Locate Transmitter) is activated the TransInd will light. If the transmit relay in your transmitter is stuck Trans-Ind will light even though the
transmit button is not pushed. Using a hand held transmitter will cause Trans-Ind to light up.
How to Use Trans-Ind
The single power button and two LED indicators make the use of the instrument intuitive and
straightforward. When Trans-Ind's power button is pushed both blue and yellow LED's will blink
during a power-on self check. The power switch is the only control; there are no adjustments or other
switches. When power is on, the blue LED is illuminated but dim, visible only in shadow.
Keying a transmitter microphone will illuminate the yellow LED. As you start to talk, the blue light
will come on.
Installation
Recommended installation is on the top of the instrument panel. The unit is supplied with an adhesive
velcro strip which will secure the indicator.
The unit can be placed on any open area of the instrument panel. A horizontal installation is
recommend because the lights are less visible when the unit is mounted vertically. Also, keep in mind
that the radio frequency energy generally decreases as you move to lower locations in the cockpit,
resulting in less reliable operation. For these reasons the recommended location is the top of the
instrument panel.
Before attaching the velcro to the desired location, the unit should be checked for reliable operation.
Small aircraft vary widely in the amount of radio energy in the cockpit and many have a few “dead
spots,” or areas with low energy where Trans-Ind will not work. To ensure reliable operation, the unit
should be checked at the low, middle and top ends of the frequencies by finding unused channels near
118, 126, and 135MHz. Tune the transmitter to the frequencies with Trans-Ind on and positioned in
the desired location. Momentarily key the microphone and make sure the yellow carrier light comes on
for all frequencies. Moving the unit sideways a few inches will usually take it out of a “dead spot” and
allow it to work normally.
These tests can be done on the ground. We recommend that the aircraft be outside a hangar, as the
metal in the hangar reflects the radio waves, causing different patterns to exist than when the aircraft is
flying. Final checking should be done in flight.
After ensuring operation across frequencies, use the velcro to secure Trans-Ind to an appropriate
surface in the aircraft.
Troubleshooting
The two problems that are most likely to arise are: 1) lights come on when not expected, and 2) lights
do not come on when expected.
Lights on when not expected:
Yellow light on, no transmit:
The yellow light can come on when there is a significant interference signal, such as an FM
radio station nearby. See the “Rejection of Out-of-Band Signals” section below.
If the yellow light is working normally and then does not go off when you let go of the transmit
button, that is an indication that you are still transmitting. Your first response is to fly the
airplane. When you can devote some attention to the problem the first thing to try is to press
and release the transmit button several times. If the light continues to stay on you should turn
off the radio power momentarily. If the light goes off when the radio is off you should leave the
radio off-unless you need to declare an emergency. Your continuous transmissions will block
whatever frequency you are using and you cannot receive. If the yellow light stays on when
your radio is powered off, there is most likely another transmitter on your aircraft that is
operating, such as an ELT or a hand held transmitter.
Another situation to be aware of is that the unit will indicate a transmission if you are on the
ground close to another aircraft that is transmitting, or you are near a fixed transmitter such as
the ATIS or other continuous source. Aircraft more than 50 feet away will rarely activate the
unit. In most cases you will be on the same frequency as the other aircraft and it will be
obvious what is happening. In any case, it is advisable to delay any troubleshooting until you
are separated from the other aircraft.
If the unit is always on when away from any source of transmissions (outside of the downtown
area for example) contact Electrical Efficiency Systems for return instructions.
Blue light on with no talking:
The blue light will flash when the battery is low. For a small range of low battery conditions the
blue light will come on whenever the yellow light is on. Replacing the battery with a new one
will fix this problem. The unit will operate several hours after the “battery low” indication
starts. Thus, it is not necessary to replace the battery during most flights.
Lights do not come on when expected:
Yellow light dark when transmitting:
In the case of the yellow light not illuminating during transmit, the most likely cause is that the
unit is in a “dead spot” where the RF energy is too low to trigger the light. In this case, a
different frequency or location will allow correct operation.
If the unit has been working normally and then stops illuminating, the most likely cause is
decreased radio energy. Any of the following will reduce output power. A corroded antenna
cable connection, low voltage to the transmitter, broken or damaged antenna or antenna cable.
A trip to an avionic shop is recommended at this point.
Blue light dark when transmitting and talking:
If the blue light never illuminates there can be several possible problems. The most likely is
that the microphone is not in the right socket. If the pilot is not speaking loud enough there may
not be enough modulation to turn on the blue light. In some cases the transmitter is not
properly adjusted for the microphone in use and needs to be adjusted by an avionics shop. The
device is designed to illuminate when there is more than 30% modulation. A proper radio setup
will result in 80% or more modulation.
Neither light comes on at all:
Most likely cause is a totally dead battery, Replace with known good battery.
If after battery replacement the unit still does not operate return contact Electrical Efficiency
Systems for return instructions.
Rejection of Out-of-Band signals
Any radio can give incorrect indications when near a high powered transmitter. Trans-Ind does not
respond to cell phones or other common hand held electronics. During testing there were two
conditions when Trans-Ind showed a carrier indication from out-of-band signals.
When operating on the ground at fields with radar, the unit will sometimes light when the radar beam
passes by. Most headsets also detect the radar, causing an audible “beep.” If Trans-Ind lights at the
same time as the “beep” it is clearly due to the radar. This false trigger is minimized by keeping TransInd as close to horizontal as possible.
As an aircraft passes close to an FM or Television transmitter Trans-Ind may light. If the unit is sitting
horizontally on the top of the instrument panel, the unit does not indicate until you are much less than a
mile away from the radio station. If the unit is mounted near door pillars or other aluminum airframe
junctions, the airframe will act as an antenna, increasing the fields and causing the unit to indicate. In
most cases, the regular communications radios will become inoperative before Trans-Ind is activated.
Specifications
Because Trans-Ind does not connect to aircraft wiring and is not permanently connected to the
instrument panel it does not need to be certified.
Frequency Range
Sensitivity
Modulation Detect
Battery Life
Weight
Size
Operating Temperature
Low battery Indication
118.00 MHz to 137.5 MHz
Unit will indicate transmission within 10 feet horizontal of a 10 Watt
transmitter.
Blue LED lights when modulation is over 30% independent of RF power
level
100 hours with an alkaline 9V battery and transmission less than 5% of
the time.
135 grams with battery installed.
3.1 X 4.75 X 0.95 inches, 78.5 X 121 X 24 mm
0 to 120 degrees F.
Blue LED flashes with battery less than 6.5 volts.
Electrical Efficiency Systems
EESys.co
503 490-5852
anguseesys@gmail.com
Battery Replacement
While the rather tight fit for the 9 V battery prevents it from vibrating and wearing the wires it is
sometimes difficult to remove. The following pictures show a technique that usually pops the battery
out of the box.