Receiver characterization

[abhijitrc]

We are facing problem in characterizing the receiver that we are not getting a proper demodulated signal from the output of the demodulator (quadrature type used), but at the output of the limiting amplifier we are getting a constant modulated (FM) signal within the dynamic range (-60dBm to -110dBm), what may be the cause ??? plz send me the application note of quadrature type demodulator

 

[Element_115]

We are facing problem in characterizing the receiver that we are not getting a proper demodulated signal from the output of the demodulator (quadrature type used), but at the output of the limiting amplifier we are getting a constant modulated (FM) signal within the dynamic range (-60dBm to -110dBm), what may be the cause ??? plz send me the application note of quadrature type demodulator

What is your system gain line up ? Your description is too vague.
Is the Antenna well matched? Is the LNA or Limiting Amp drawing too much or too little
current ? What is the Frequency range ? ......

Can you use a CW tone to check your RF Chain ?

 

[abhijitrc]

Total gain of the receiver is 120 dB.and the front end is operating on 14.5GHz and down converted to 595MHz and and second downconversion leads to 160 MHz, our receiver id FM type ( two stage downconverted)

 

[Element_115]

Total gain of the receiver is 120 dB.and the front end is operating on 14.5GHz and down converted to 595MHz and and second downconversion leads to 160 MHz, our receiver id FM type ( two stage downconverted)

At 14.5GHz it is going to be tough to debug. Do you have some sort of Probe to sniff the
signal as it goes through the Receiver ? I only know of the HP-85024A that only goes up to
3GHz. You can use this one for the 1st IF and second LO and second IF. If you determine
that the 1st & 2nd IF and 2nd LO are good then you will at least know that the problem
is between the input and output of the 1st mixer.

Also I would first try to confirm that the RF chain / Hardware is working using a CW signal
before I would add the modulated signal. Some times you can see where the problem is
when you switch between modulated and unmodulated signals. Can you compare this Rx
to a know good Rx unit ?

 

[abhijitrc]

upto second IF stage i used carrier signal and found that carrier is through and the gain is 120dB, but once modulation is ON and we checked at the output of the demodulator, we are not getting a proper signal especially at the higher end of the dynamic range?(-60dBm to -65dBm)

 

[BigBoss]

upto second IF stage i used carrier signal and found that carrier is through and the gain is 120dB, but once modulation is ON and we checked at the output of the demodulator, we are not getting a proper signal especially at the higher end of the dynamic range?(-60dBm to -65dBm)

If overall gain is 120dB, how you would you expect 60dBm output power when you apply -60dBm input power ??
It's obvious that your amplifying stages are saturating therefore you loose IQ modulation information...