[SOLVED] help me making RF receiver circuit ,,,

[amrshata]

i want to make 2.4 gh receiver ,,, i really don't know what to do is there is away that i could change the circuit of router to a receiver or is there is circuit ,,, or should i decrease the freq is so to which freq

 

[Terminator3]

It depends on what do you want to receive. For example, there are ready to use 2.4GHz ICs, such as nrf24l01 and CC2500. You can receive another nrf24l01 chip based TX signal without a problem, if you have the same chip and know channel number. If you want to receive WiFi, it would be difficult, i read magazine about some routers use Linux system (so it can be altered) and some drivers for notebook can be altered to receive raw unprocessed data.

But there is also another interesting possibility. You can take CC2500 chip, it have better frequency/channel tuning range resolution than nrf24l01. Then use commands to put it in CONSTANT UNMODULATED carrier mode, and some commands to choose channel. Take schottky diode, something like BAT14 (actually it is too good for this, you can try another cheaper one). Make single balanced mixer (or even simpler mixer) using microstrips. Then you can connect CC2500 antenna output to one port of schottky diode mixer (LO, local oscillator port), and some antenna to another port of mixer (RF port). IF port of mixer gives you some low-frequency signal, you can amplify it by any available OpAmp IC, and put to microphone port of your computer. In this scheme CC2500 works as very stable LO (local oscillator). For simple experiment you can connect RX antenna and shcottky directly to output of CC2500, it becomes some kind of lame self-mixing antenna mixer =). This way you can hear some beeps of wireles mouses and other stuff.

To build more advanced system you will need 4 shcottky diodes (2 x 2-series), make double-balanced mixer, and produce an IQ-receiver with two channels, then use two OpAmps and put signal to stereo microphone input of computer for further DSP processing.

 

[amrshata]

really thanks that's very helpful

i'm making jamming locator device it's basic idea depends on receiving signal from array antenna and perform some operation on the signal

so i need an antenna first to accept the signal then pass to rf receiver consists of mixer,oscillator and amplifier then pass the signal to ADC then get the IQ

then from the IQ output i will perform my circuit ,,, so i need an RF receiver that doesn't make modulation just i want the IQ output so please answer me

and about the circuit you discussed above using cc2500 here we get I Q ,, or an low freq signal or an digital signal .... if it's possible can you show me shematic or help me with any link of what your talking about

- - - Updated - - -

CC2500 features a low-IF receiver. The
received RF signal is amplified by the lownoise
amplifier (LNA) and down-converted in
quadrature (I and Q) to the intermediate
frequency (IF). At IF, the I/Q signals are
digitised by the ADCs. Automatic gain control
(AGC), fine channel filtering, demodulation
bit/packet synchronization is performed
digitally.




so if it's possible i want to get the output of ADC directly not pass to the modulator part or any other following blocks

 

[amrshata]

any help
????

 

[Terminator3]

I mentioned CC2500 as a simple replacement of VCO, as far as i know there is now way to get IQ output from that chip.
to receive:
1) some stable local oscillator. It can be VCO MAX2750, or CC2500 (used as a dummy oscillator, other functionality can't be used). Amplify it with some IC or FET. For simplicity. Or you can make VCO using varactor and FET.
2) balanced IQ mixer. You can make it using microstrips and Schottky diodes, or use integrated IC like Hittite or something (as CC2500 have no such output pins, so you need external balanced IQ mixer)
3) put I,Q output of mixer to 2 channels of ADC and

You can search for how amateur GHZ-range transceiver work, there are many materials on amateur radio.

To perform something on received signal and send it back in microwaves is more difficult. The only approach i know is used in some RFID schemes. It based on fact, that any incoming signal can be amplified and then modulated (by balanced mixer, altering AC on IF outputs that become inputs), as if it was your own local oscillator. After that modulated signal can be perfectly received by the original oscillator scheme.