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*Subject*: Re: Path loss and signal calc...*From*: Raul Gomez Fernandez <raul.gomez@xxxxxxxx>*Date*: Thu, 05 Feb 1998 12:10:42 +0100

The equation of losses in free space is: losses= ((4*pi*d)/lambda)^2 (it's elevated to square) pi: 3.14159.... d:distance lambda: wavelenght In a simplier equation: losses (dB)= 32.45 + 20 log f (MHz) + 20 log d (Km) This give the total losses in dB if you put frequency in Megahertz and distance in Kilometers. Then, to calculate the receive power, you have: P_rx(dBm)= P_tx (dBm) + G_tx (dB) + G_rx (dB) - losses (dB) (All this without consider other losses than it produces distance) You can join P_tx + G_tx as EIRP (PIRE in spanish). To calculate the minimum recepcion power of you receiver from the SINAD, you have: i.e: Minimun voltage on you receiver 0.2 uv Imput Impedance 50 Ohms (consider that antena impedance and receiver impedance are matched) P_rx_min=(V*V)/Z= (0.2*10^-12)/50=8*10^-16 watts in dBm: P_rx_min (dBm)=-121 dBm If the P_rx is greater than your P_rx_min you can receive something, if it is not greater you must increase your Pr_rx adding preamps, better antenna, etc .... I hope this can help to your questions. About losses in a ionospheric propagation is difficult to explain in a message because are included too many factors. 73. Anthony Bombardiere escribió: > Hi all, > > AF9Y calculated the path loss for the Mars probe at -179dbm. > If the average receiver has a minimum disernable signal of -140dbm. > How can one hear a signal thats -39db below the receivers noise floor? > > I would assume that antenna gain and any pre-amplification > is taken into account, and the fact that Mike,(AF9Y) used his DSP > program to graphically display this signal that could not be heard > by the human ear , but how can one receive a signal that is far > below that of the receivers noise floor? > > Is the calculation for this problem as simple as taking the > preamp gain and antenna gain and adding them to the path loss > of the signal? If so, assuming a total gain in the system of > 50db then.... > > -179dbm + 25db(pre-amp) + 25db(antenna gain) = -129dbm ????? > > Also, if the sensititvity of a receiver is said to be .2 micro > volts at (10db s+n/n), that would mean that the receiver would > produce a signal of 10db above the noise for an input of .2 uv. > How can one relate this mesurment with signal strengths > that are expressed in dbm or decibles as they relate to microvolts? > That is, how does a signal that is said to be -140dbm relate to > the measument of .2uv at (10db s+n/n) > > Its obvious that I'm not sure of my math skills, but I had to > ask... > > Thanks , AB2CJ -- Raul Gomez Fernandez .-.-.-.-.-.-.-.-. EB4GZO ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Email_1= mailto:raul.gomez@coitt.es Email_2= mailto:rgf41@rcua.alcala.es ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ P.O.Box:55.180 - C.P.:28.080 - Madrid - Spain ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

**References**:**Path loss and signal calc...***From:*Anthony Bombardiere

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