Hello everyone,

I am studying telecommunication electronics and i can't seem to understand how frequency synthesizers and mixers are used. I can understand how they work separately, but can't see how they could fit in a RX system. The synthesizer is used in the PLL of the RX in order to "jump" between frequencies and lock at different channels, right? The mixer also provides different frequencies based on the LO and the received signal, so by manipulation the dc voltage of the VCO we could still get a number of different channels. That is what confuses me. Are they used in the same system? For example, does a GSM receiver use both of them, and if so how?

Also, how do the concepts of up/down conversion apply to those? Why do we use a mixer to up/down-convert and not a synthesizer?
Lastly, why do we perform down/up conversion? Is it to adjust the frequency in order to work with our low-end electronics?

I know these are a lot of questions, but i hope someone could clarify these concepts to me.
Thank you for your time!

 

To turn question around, how would you use a synthesiser to up or down convert a signal ?

why do we up / down convert the frequency you ask .
well, what is the frequency range of the signal you want to say transmit ?
what is the frequency of the transmitter ?

 

Hello there
Is this homework? doesn't sound like homework!
But you really should research Super Heterodyne.
Up Converter
- Up conveter is a part to convert signal up for transmission. Basically, mixer part for frequency upward conversion is called UP CONVERTER. When input signal combines LO signal, RF signal is generated as much as input signal with LO signal.

Down Converter
- Down converter is a part to convert RF signal down to IF or baseband. Basically, mixer part for frequency downward is called down converter. When input signal combines LO signal, IF or baseband signal is generated as much as Input signal to LO signal. In some cases, down converter includes LNA and specilly it even includes LNA and buffer AMP in satellite equipment

 

Hello there
Is this homework? doesn't sound like homework!
I would gladly answer your question!
But you really should research Super Heterodyne.
Up Converter
- Up conveter is a part to convert signal up for transmission. Basically, mixer part for frequency upward conversion is called UP CONVERTER. When input signal combines LO signal, RF signal is generated as much as input signal with LO signal.

Down Converter
- Down converter is a part to convert RF signal down to IF or baseband. Basically, mixer part for frequency downward is called down converter. When input signal combines LO signal, IF or baseband signal is generated as much as Input signal to LO signal. In some cases, down converter includes LNA and specilly it even includes LNA and buffer AMP in satellite equipment
View attachment 241845


View attachment 241846

I think I got it now! So the synthesizer is in the LO signal (PLL) in order to switch to different channels. The mixer takes the reference LO and down/up converts the received signal. So a new question arises, does the mixer do that conversion in order to work with lower end electronics, or does it perform demodulation?
From what I have read, for down conversion, the mixer subtracts from the received signal the "carrier", is that right ? So, in up conversion, does it practically "load" the information to the carrier signal ?
If so, how does the RX recognize the carrier freq ?
Thanks !

 

Okay you mentioned GSM.
My crystal ball says you are interested in a GSM and Arduino based Home Automation using SMS?
Only because I was to answer all of your questions in a very efficient manner,

In other words In one post & less than 10,000 words.

 

Phase Locked Loops (PLL) is a closed loop system that locks two signals
in such a way that exist with same
frequency and constant phase (zero) difference between them.
The system compares the frequencies of an input waveform to that of
the output of PLL and then adjusts the
frequency of output such that
they are totally synchronized with each other. PLL consist of three parts:
Phase Detector, loop Filter and a Voltage Controlled Oscillator (VCO).
The VCO helps in changing the output frequency and provides frequency equal to the frequency of incoming signal.
PLL locks two signals in such a way that they are synchronized with
each other.
The incoming signal in the reference or input signal is the frequency that is to be adjusted so that it can match the reference signal and feed to VCO.
The function of the phase detector is to produce an error signal
based on the difference in phase
value between the input signal and the reference signal.
The phase detector is a multiplier circuit and producing additional signal.
Local oscillator (LO)Produces a local signal offset from incoming (RF)
signal) by Intermediate Frequency (IF) Combined with incoming
signal in Mixer to produce the IF.
Has two inputs – RF signal and Local Oscillator (LO) One output &
Intermediate Frequency (IF).
A Mixer produces an output equal to the difference of the input signals.
Or the Difference of two frequencies.
(IF)Intermediate Frequency.
Provides gain and Selectivity at IF.
A Detector demodulator Recovers modulation from the signal. New record only 9,999 words. And a face