Week 1 Flashcards
What is the audio that comes from comm radios/nav equipment for identification?
Received Audio
What is the Received audio output impedance for headphones and speakers?
500-600ohms for headphones
3.2-8ohms for speaker
What is the audio that is heard on headphones and is a conversation between crew members? Can either be ICS, VOX, or PTT
Interphone audio
What is the interphone audio output impedance?
500ohms
What is the audio that is pretty much feedback and is the audio heard on the headphones of crew while tx
Side tone audio
Is the side tone audio level adjustable by the pilot?
No
Where is the side tone audio adjustable?
Radio bench
This audio is low level, 0.15-0.25VAC that is created by speaking into a mic
Microphone audio
In microphone audio, what changes are you looking for in the line?
Change in voltage or resistance
When testing what should you never use?
Never use pilot mic or headphone
Use a known serviceable mic and headphone
How would you test the audio integrity in the aircraft?
Load a mic and phone jack with resistors until the measured V is half its unloaded value, this gives you the IMPEDANCE of a circuit
Why is there a voltage in the mic audio line?
To give the mic a power to operate
Headphone impedance is what?
500-600ohms
What are the 3 types of microphones?
Electret
Dynamic
Carbon
Which of the microphones require an amplifier and why?
Electret and Dynamic
They only produce mV outputs
How does the electret microphone work?
sound = diaphragm vibration = distance btwn diaphragm and plate = electric signals
capacitance change
How does the dynamic microphone work?
A diaphragm moves a magnet/coil which creates a current
Electromagnetic effects
How does the carbon microphone work?
sound = carbon compressed by diaphragm = resistance change = current flow
What are the 3 parts of a jack?
Tip, Ring, Ground/Barrel
Which part of the jack is the PTT and what does it do?
The tip
When PTT is activated, tip is grounded which then we go from Rx to Tx
Which part of the jack is the audio?
The Ring which has a DCV supplied from radio
Which part of the jack is common to the PTT and audio?
The ground
Aircraft microphones require a bias voltage of?
9V
Microphone impedance is what?
150ohms AC
Typical output voltage of microphones are what?
1Vrms
Which microphones can you change the output of?
Electret and Dynamic
Typical frequency response for headphones is what?
3kHz to 300Hz
Headphone has how many ohms in the input and output?
500 in 500 out
Speaker has how many ohms in the input and output?
500 in and 3 out
Mic has how many ohms in the input and output?
150 in and 500 out
What is howling?
When the mic is too close to the speakers
On a speaker amp test, how do you set it up and what are the outputs?
1Vrms and 1kHz signal from audio gen
should see 1V in and 1V out
For the speaker amp test, when should distortion happen?
between 5-6V
On a headphone amp test, how do you set it up and what are the outputs?
1Vrms and 1Khz signal from audio gen
1V in and 1V out
During a headphone amp test, when increasing the voltage to 5 what happens?
No distortion
On a mic amp test, how do you set it up and what are the outputs?
- 5Vrms and 1kHz signal to mic jack
0. 5V in and 2.5V out (around 5x gain)
On a mute function test, how do you set it up and what is the output?
`3Vrms and 1kHz signal
operating ptt = mute
What is the bandwidth test?
Set 1kHz as reference then increase/decrease and see where the power goes to 1/2 or 70% (0.7V out)
For power conversions what are the decibels?
3dB and 10dB
For voltage conversions what are the decibels?
6dB and 20dB
What is the reference level for dBm units?
1mW
What is the reference level for dBw?
1W
