RX path noise on adjacent channel in GSM !?

[Wilson_yu_chen]

gsm adjacent channel

Hi guys,

I met a problem with adjacent channel rejection failed in GMSK modulation
for EDGE mode while pass for GSM mode. Many points that I would check, but
one of them would be only adjustable by me, RF system worker, is
to change AGC/Front-end gain plan.

I'm wandering this way would made noise difference by lowering front-end gain
while making PGA cascaded gain higher ?

Or any other points that you can recommend ?

Thanks!

 

[vfone]

One thing that could help you is to improve the IF or Baseband filtering.
In direct conversion receivers if the level of the adjacent interferer is too high at the input of the A/D converters, the adjacent signal fold back into the desired channel.
Also be sure that for the measurement test you are using the right level for the desired signal.

 

[Wilson_yu_chen]

Hi vfone,

It's a pity to me that IF filtering is no parameters changeable.
But may I know what's the next if that adjacent jammer back to the desired
signal ?

For adjacent-ch rej. spec C/Ia, what I can do is to lower the Ia, but
nothing I can do but adjust AGC/front-end gain.

Any comment?

Thanks!!