George, this formula is valid only for free space propagation but it is correct for all frequencies. The 20LOG(Freq) part takes care of the fact that the capture area of the receiver antenna decreases as 20LOGF. As you know, there is not really a difference in path loss as frequency is increased. That is, if I transmit a signal at two different frequencies and both have the same E-field amplitude at point A, they will both have the same E-field amplitude at point B, along the path of propagation. Here is a link to a program that claims to solve for surface wave propagation at MF and HF: http://www.btinternet.com/~g4fgq.regp/ You want to find GRNDWAV3 Another way to explore surface wave path loss is to use NEC (I use NEC-2) and set up the appropriate antennas at each end of the path. Apply power to one and measure the current (power) in the other. It will solve for a flat path of course and doesn't take the curvature of the earth, or obstacles into account. Also, I am told that the far-field ground modeling of NEC-2 is not the same as for near-field and so it isn't true-to-life. However, it might be a good way to explore different antennas and ground types to get a feel for the issues. Dave Cuthbert Micron Technology
From: [email protected] mailto:[email protected]] On Behalf Of George Stults Sent: Thursday, December 02, 2004 11:48 AM To: [email protected] Subject: path attenuation in AM band Hi Folks, I have an equation for the attenuation of a radiated signal as a function of (distance, frequency, and environment.) ATTN = 37 + 20 Log (Freq) + 20 Log (Dist), Freq is in MHz, Distance in Miles, Environment is free-space/line-of-sight (N=2). My information is that this equation works well for 2.4GHz frequency range. Could anyone tell me whether this equation would still make valid predictions for attenuation in the AM band. (535 – 1650)Khz, and lower? Or could anyone suggest an equation that would predict path loss as a function of distance, frequency, and environment for lower frequencies? Thanks in advance. George Stults ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Ron Pickard: [email protected] Scott Douglas [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
