This question was asked in Electrical Engineering 2 days ago but hasn't received very informative responses. https://electronics.stackexchange.com/questions/387255/decide-coherent-time-and-fade-duration-through-empirical-studies-on-the-channel

I. Scenario: - TX floating in the lossy heterogeneous medium (a mud-like fluid mixed with leaves and small rocks) with undetermined positions within a limited region; - RX fixed in the air and closed to the boundary of air-lossy medium; - Frequency 500 MHz

II. The study: - The received signal level was recorded every 30 seconds for 30 minutes and sometimes no signal could be detected for a while. The measurement was repeated several times.

III. Results: An example of the received signal spectrum is as below. enter image description here


  1. Can I assume 3 minutes to be the coherent time of the channel?
  2. Can I assume the no-signal period to be fade duration?
  3. How to model the channel when the TX-RX distance was not stable? Can I develop a model for the changes of received signal against time?
  • $\begingroup$ What are the distances involved and what is the transmitter power? $\endgroup$
    – Glenn W9IQ
    Jul 25 '18 at 15:22
  • $\begingroup$ The distance could be in-between 0.5 to 3 meters. The transmitter power was set to be 18 dBm. $\endgroup$
    – luw
    Jul 25 '18 at 16:16
  • $\begingroup$ At that distance and power level, what then is the cause of signal loss? The viscous medium, the antenna patterns, receiver sensitivity or ??? $\endgroup$
    – Glenn W9IQ
    Jul 25 '18 at 16:40
  • $\begingroup$ Basically it's the watery medium while the Tx antenna is too small to be a good radiator. The receiver is a spectrum analyzer which I guess should be fine. $\endgroup$
    – luw
    Jul 25 '18 at 22:29

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