Contents


The Microair 760 is a very lightweight [0.4 kg] low power consumption [87 mA receive] panel mounted COMM transceiver.

The first two sections in the following material are an edited extract from the Microair 760 manual: the full manual can be viewed on the Microair Web site.



 

4.1 Control Functions

Microair 760 front panel

1. Priority Switch
The priority switch is a push down switch designed to activate an emergency frequency. When pushed down briefly, the radio will go into memory mode, and select the frequency the user has stored in the memory 25 position – usually the international aviation distress frequency 121.5 MHz.
2. Volume / On / Squelch Knob
The MA-760 is turned on, by rotating the volume knob. A positive “click” is heard and felt at the start of the rotation to indicate the on/off position. The volume is increased by rotating the knob clockwise, and decreased by rotating counter clockwise.

The squelch is adjusted by rotating the ring behind the volume knob. There is no automatic level set for the squelch, however the ring affords a large manual adjustment to suit all situations. Rotate the ring clockwise to increase the squelch threshold, and counter clockwise to lower the threshold. When the squelch is “broken” (ie the static hiss can be heard), the annunciator light emitting diode [LED] lights green.

Note: This does NOT mean you are receiving a signal on the selected frequency!
3. Receive / Transmit Annunciator
The LED operates red or green, and indicates the following states:
  • Clear (off): Radio is squelched above the threshold, and is not receiving a signal


  • Green: Squelch is broken or a signal is being received


  • Red: Radio is transmitting


  • Flashing Red: Radio has transmitted for over 30 seconds (warning)
The flashing red signal may draw the user’s attention to the fact that the aircraft may have a stuck PTT button! There is no likely scenario where a valid transmission exceeding 30 seconds would be required.
4. Mode Switch
The mode switch is a push down switch. When pushed down briefly the radio will step to the next operating mode. The MA-760 has four operating modes:
  • Toggle mode
    The display shows the active or in use frequency on the top line. The standby frequency is displayed on the bottom line.
  • Memory Mode
    The top line displays the memory [MEM] position number, and the lower line displays the frequency for that memory. The displayed memory becomes the frequency the moment it is displayed. The user can scroll through the programmed memories by rotating the frequency adjust knob, or by pressing the [optional accessory] remote memory button.
  • Program Mode
    The MEM is replaced with PROG on the top line. The frequency stored in each memory can be set, changed, or cleared in this mode (refer memory programming).
  • Scan Mode
    By holding down the toggle switch for 3 seconds, the MA-760 goes into scan mode. The programmed memories are cycled quickly across the display. The MA-760 checks each memory in turn for any signal. If there is no signal the radio moves to the next programmed memory. When a signal is detected, the scan locks to that memory to receive the signal. This memory is held for 10 seconds after the signal finishes to afford the user an opportunity to reply on that memory channel. The user can stop the scan operation by pressing down briefly the toggle key, or the PTT button.
5. Frequency Adjust Knob
The standby frequency can be changed by scrolling the frequency adjust knob. Rotate knob to scroll the MHz half of the standby frequency. Press the knob in briefly to move the cursor to the kHz half of the standby frequency. Rotate the knob again to scroll the kHz. After 5 seconds of inactivity the cursor will move back to the MHz side of the standby frequency. Only the standby frequency can be changed directly, the active frequency cannot be directly altered by the frequency adjust knob.
6. Toggle Switch
The toggle switch is a push down switch. When pushed down briefly, the active and standby frequencies exchange places. Hold the toggle key down for 3 seconds to activate the scan function.
7. Liquid Crystal Display
Two lines, each of eight characters of information. In normal operations the active frequency appears in the top line and the standby frequency in the lower line, as shown.

4.2 Operating procedure

The MA-760 should always be turned off, before starting the aircraft to protect the radio from transient voltages.

Pilots should monitor 121.5 MHz before engine start and after engine shutdown, to check for transmissions and to ensure that your own distress beacon is not activated.

After starting, the radio can be turned on, and the squelch adjusted so the static hiss can be heard. The LED annunciator will light green while the hiss is heard. Use the hiss tone to adjust the volume to an appropriate level. With the volume set, turn the squelch ring to break the squelch and eliminate the hiss. The LED annunciator light will go clear.

The intercom volume is pre-set, and not affected by the volume knob.

The MA-760 can now be adjusted to the correct active and standby frequencies, by scrolling and pressing the frequency adjust knob.

The MA-760 will transmit when the PTT button is held down. The LED annunciator will light red. When transmitting the user will hear themselves speaking through their own headphones via the sidetone system.

If the transmission lasts longer than 30 seconds, either because you have a lot to say, or because the PTT has stuck, the LED annunciator will flash red. When this happens, check the PTT immediately. If you find no obvious fault, turn the radio off, and then on again. If the LED is still red, turn the radio off and leave it off.

4.3 Fault tracing

Pre-flight check
The following check list is applicable to all handheld and fixed panel-mounted transceivers and associated system components:
    1. No apparent power
  • All necessary main/avionics power switches ON?
  • Transceiver switch ON?
  • Aircraft battery/transceiver batteries drained?
  • Fuse blown /circuit breaker popped?
    2. No background hash heard
  • Volume turned down?
  • Squelch set too high?
  • Headset correctly plugged?
  • Headset compatible with transceiver?
  • Earpiece volume controls turned down?
  • Antenna missing or damaged?
  • Antenna feedline coax correctly plugged in at both ends?
    3. No signal reception or transmission response
  • Correct local frequency set as active?
  • Other stations [e.g. airfield Unicom] not listening out?
  • Squelch set too high?
  • Volume turned down?
  • Loudspeaker too far from ears?
  • Microphone compatible with transceiver?
  • Microphone not close to lips?
  • PTT or mic switch inoperative?
  • Airframe structure blocking signal?
  • Airfield structures blocking signal?
Interference problems
When airborne, continuing excessive background crackle, hum or howling heard in the headset/speaker is usually associated with the components, active wires and ground wires within the electrical system. The engine ignition system may also be a source of RF interference. The identification of the cause, and the fixing of the problem/s, may well be a difficult and protracted process requiring expert help.