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Technology Stocks : LAST MILE TECHNOLOGIES - Let's Discuss Them Here -- Ignore unavailable to you. Want to Upgrade?

To: Raymond Duray who wrote (6439)	2/16/2000 11:04:00 PM
From: wonk	Read Replies (4) \| Respond to of 12823

Scott, Ray: If both of you have pure line-of-sight (LOS) the calculation runs like this: Using the Freewave spec, freewave.com and running separate calculations for the 900 and 2.4 MHz unlicensed bands: 1. Receiver Threshold, 10-6 BER (dbm) -108 2. Receiver Antenna Gain (dB) 0 3. Transmit Antenna Gain (dB) 0 4. Transmitter Output Power (dBm) 30 5. Addition Margin for 90% Probability (db) 9 6. Interference Degradation (dB) 0 Total Sustainable Path Loss (dB) 129 So absolute value of (1) + 2 + 3 + 4 minus 5 minus 6 (assuming you input 5 and 6 as positive numbers). Then, Free Space Loss (FSL) = 36.6 + 20 * log (frequency in MHz) + 20 * log (distance in miles) Assuming a distance between xmit and receive of 21 miles the results are as shown. Frequency 928 2450 Sustainable Path Loss (dB) 129.0 129.0 less: FSL (dB) 122.4 130.8 Link Margin (dB) 6.6 -1.8 So at 900 MHz with "pure" LOS, the link should work; at 2.4 Ghz it's iffy. I say iffy because of the fudge factor (addl margin for 90% probability) which really isn't necessary with pure LOS. However, one really doesn't know if one has pure LOS w/o an analysis of fresnel zones. Also, since you are both in rural areas there likely is not much co-channel interference (which becomes a real killer as the band loads.) Note that this is for outside. If you want to go through the first wall of your home add another 9 dB of loss and additional loss as you go deeper. Pretty easy to run your own calculations or build a spreadsheet from here. (And trust I haven't made any mistakes <g>) Have fun hiking.... ww