Thanks for your reply. According to my measurement, there can be a few dB's difference for the same link using different channels such as 19 and 26.
I have two additional questions:
1) Does signal attenuation depend on transmission power? Based on my limited knowledge of physics, it does not. However, in measurement, noticeable difference is observed.
For a sender and receiver, the measured signal attenuation of the link is 56 dB when the sender transmits at power level 3 while the signal attenuation for the same link is 57 dB at power level 31.
2) Another related question, according to CC2420 datasheet, the tx power is -25 dBm when power level is 3. Is the actual tx power equal to -25 dBm or there is some deviation depending on the specific hardware? How large is the typical deviation if any?
Look forward to your explanation. Thanks in advance.