PTT അമർത്തിയാൽ റേഡിയോക്കുള്ളിൽ സംഭവിക്കുന്നത്, ഘട്ടം ഘട്ടമായി. A simplified view of a typical FM handheld; real radios differ in the details.
Press and hold
Pressing PTT powers the transmit circuits and moves the antenna switch from the receiver to the transmitter.
- MicrophoneVoice becomes a tiny electrical signal
- Audio amplifierMakes that signal bigger
- OscillatorMakes the carrier wave, e.g. 145 MHz
- ModulatorVoice changes the carrier. In FM it changes the frequency
- Power amplifierRaises the signal to watts
- FilterRemoves unwanted waves before they reach the antenna
- AntennaTurns the current into radio waves
Never transmit without an antenna connected. The power has nowhere to go and the radio can be damaged.
Release the button
Releasing PTT switches the antenna back to the receiver and the transmit circuits switch off.
- AntennaPicks up weak radio waves
- RF amplifierStrengthens the wanted signal
- Mixer + filterShifts it to a fixed lower frequency and selects one channel
- DetectorRecovers the voice from the carrier
- Audio amplifierDrives the speaker
- SpeakerVoice again
The units you will meet
| Unit | Measures | Good to know |
|---|---|---|
| Hz, kHz, MHz | Frequency | Cycles per second. 145 MHz is 145,000,000 cycles every second. |
| W, mW | Power | Transmit power. 1 W = 1000 mW. |
| V, A | Voltage, current | Supply and signal levels inside the radio. |
| Ω | Impedance | Radios, coax and antennas are usually matched to 50 Ω. |
| SWR | Match quality | 1:1 is a perfect match; higher means more power reflected back. |
| dB | Gain or loss | +3 dB is about double the power, +10 dB is ten times. |
Wavelength
wavelength (m) ≈ 300 ÷ frequency (MHz)
At 145 MHz that is about 2 metres, which is why this is called the 2 m band.
Made for the Captain.Ramkumar reel series. Always operate only on frequencies and power levels your licence allows.
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