testing rx on gsm
I have GSM850 band TX noise in RX band noise level over spec problem.
What I have done:
1. Check PA input or VCO output and see noise level within the spec.
2. Skyowrks PA pedestal level would impact that noise level too.
What shall I do ?
Thanks!
GSM-850 specification for noise power is -79 dBm, in the frequency band 869 MHz to 894 MHz using a RBW of 100kHz. Check that you use the right RBW for the measurement.
For this test you need a notch or a band-reject filter to reduce the TX carrier. In this way you can increase the dynamic range of the measurement. The Noise Floor of the Spectrum Analyzer in 100kHz RBW shall be lower than -90dBm.
The modulator, the VCO wideband noise and the Power Amplifier could affect the noise power in receive band.
Years ago I had some problems with Skyworks PA?s passing this test. I would recommend evaluating the PA stand-alone for this test to be sure is no problem with it.
Thanks Vfone.
Due to Locosto TXVCO sensitive to output matching, originally I suspect this
path and verified by soldering VCO output in test mode TX where I can found normal noise level.
For PA itself, could you please hint me what can I do for it ?
1. Take a High frequency probe and see the noise level in VRAMP input of PA ?
2. PA pedestal level tweak ? ( I use SKY77318 (similiar with 77328))
3. What else ?
Thanks in advance.