- Sound vibrations are received by the microphone and converted into electronic waves,
- The electronic waves from the mic are amplified by the audio amplifier producing a larger audio signal,
- The audio signal is modulated with a carrier wave produced by the RF OSC by a modulator circuit, the result is a modulated wave,
- To strengthen the power of this modulated wave, a power amplifier is used,
- The modulated wave whose power has been amplified is directly transmitted through the transmitting antenna.
Following is the block diagram of the circuit:
AM Transmitter Concept
AM (Amplitude Modulation) is divided into 2, namely:
- SW1 and SW2 (short and wave), which have frequencies ranging from 2Mhz - 11Mhz
- MW (middle wave), which has a frequency ranging from 550KHz - 1600KHz.
Formula for Determining the Length of a Transmitter Antenna
1/4, 1/2, 1 of the wavelength (strategic and effective size).
TELEPHONE TECHNIQUE
New Connection Installation (PSB)
PSB is carried out on new customers who have received a new number, the PSB work sequence is:
- Jumping cables from horizontal numbers originating from the central, primary cables in the MDF to the destination cable house,
- Jumping the primary to secondary channels to the cable house to the distribution point (DP),
- Pulling the DW cable (drop wire) from the DP to the limit terminal box (KTB) at the customer's house,
- Installation of indoor cable installation from KTB to Rosette.
Additional Network
Installing additional networks in new locations, both primary and secondary cables, must take into account the network capacity.
Network Disruption
This is an incident where two-way telephone communication does not take place, this disruption occurs because:
- Disconnection, caused by nature (natural factors), human interference (human error), and interference can occur at all locations.
- Rusty connections,
- Loose connection,
- The tool does not work, this can happen due to materials (bad / damaged components),
- Poor contact (dirty conduct), this can occur due to poor installation, usually occurs in DP, RK and cable networks.
How Does the AM Wave Frequency System Work?
Substance:
- AM Wave Frequency Spectrum Consists of 3 Parts
- AM Wave Frequency Spectrum Shape
- How to Calculate and Draw a Spectrum
- AM Transmitter
- Block diagram of AM transmitter
1. The AM Wave Spectrum Consists of 3 Parts:
- Carrier frequency / Frequency Carrier (FC)
- Lower sampling band frequency (FLSB)
- Upper sampling line frequency (FUSB)
FC = FM + FLSB atau FC = FUSB - FM
FLSB = FC - FM dan FUSB = FC + FM2. AM Frequency Spectrum Shape
PLSB = PC - PSB
PUSB = PC + PSB
3. Example of How to Calculate and Draw a Spectrum
The total power of an AM signal is 1000W.
- Determine the transmitted power at the carrier frequency and also the power on each sampling path (PLSB and PUSB) if the modulation index is 100%.
- Make a sketch of the frequency spectrum!
It is known:
- Pt = 1000W
- m = 100% = 1
Asked:
PC, PLSB, PUSB & Frequency Spectrum ?
Solution:
Pt = PC (1 + m2/2)
PC = Pt / 1 + m2/2
= 1000/1 + I2/2
= 1000/ 3/2
= 2000/3
= 666.7 W
Pt = PC (1 + m2/2)
= PC + m2PC/2
PSB = PLSB + PUSB / m2PC/2
PLSB = PSB/2
= m2PC/2 / 2/2
= m2PC/4
= 1 x 2000 / 3x4
= 2000/12
= 166.7 W
PUSB = PLSB
= 166.7 w
Frequency Spectrum:
4. AM Transmitter
An electronic device consisting of Audio production, Radio (high frequency) and Amplifier, the Audio production section consists of a microphone, AF amplifier, while the AF section consists of an Oscillator --> Buffer and the Amplifier section consists of a Modulator, RF Amplifier, and Antenna.
5. Block diagram of AM transmitter
Information:
- OSC: to produce or generate high frequency (RF)
- BUFFER : strengthens the RF signal
- MODULATOR: to modulate the RF signal with AF so that it becomes AM
- AMPLIFIER: to strengthen the AM signal.