I expect an AGC problem with CC1101, configured in async mode and receiving frames transmitted by garage door remote controls (manchester, OOK, about 1kbps, no preamble, no sync, frame is 12-30 pulses long, with 10-20ms blank between frames).
When I connect the receiver to a AM signal generator with 1KHz modulation signal, I always get -120dBm of conducted sensitivity when I set BW 100KHz, and -110dBm when using BW 270KHz. Demodulated signal appears perfect at 303, 433 and 868 MHz as well.
When I connect a lambda/4 wire to the CC1101 receiver and to RF generator, radiated sensitivity is very good in all frequency (-70dBm power on the RF generator is sufficient to see the square wave on the demodulator: distance from antennas is less than 1m).
When I try using remote controls, performances are:
* perfect at 868 MHz: very long range (400m)
* a bit lower range at 433MHz, but good. (250m)
* very very short range at 303MHz. (40m)
I believe there is a problem with AGC: please note that there's a huge blank time between frames, 10-30ms, so I understand that the first frame can be missed (and used by the CC1101 to setup the gain of internal LNAs) but next frames are easily received only at 433 and 868MHz.
What I don't understand is why the receiver performs very very well at 868, and very very bad at 303 MHz. The only difference in my configuration is test0 that is set to 0x0b (at 303MHz) instead of 0x09 (at 433/868MHz).
Please could you explain me what is the difference inside CC1101 from 303 MHz and 433/868 MHz (I believe another VCO is selected, right?) ? Why AGC works well at 433 and 868, and works bad at 303MHz?
I've setup AGC to be very slow: fsctrl1=0x04, agcctrl2=0x06, agcctrl1=0, agcctrl0=0xf0 and bitrate=2400bps
Trying with higher IF frequency or different AGCCTRLx values (as suggested by DN022) lead to poor results.
I look forward for your information or suggestions!
Thanks a lot.