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#11
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spectral power density
On 1 May 2006 06:47:45 -0700, "electro"
wrote: under unlicensed 2.4GHz FCC part 15 for digital modulation system(non-spread spectrum), it says that the 1. maximum conducted power is 1W 2. the spectral density be not greater than 8dB for every 3khz band during continous transmission 3. the 6-dB bandwith is at least 500khz question: 1. what is spectral density in this sense and its significance? 2. how can i measure my spectral density? 3. how does 1, 2 and 3 relate to each other? I downloaded the FCC's Part 15 regulations and have concluded: 1) They do say 500 kHz bandwidth 2) They do refer to +8dBm - not 8 dB 3) I agree with Tom's response |
#12
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spectral power density
typographical error.8dBm makes more sense...thanks
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#13
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spectral power density
If your modulation spreads the power evenly over 500kHz, if I
understand the rules right, you can transmit 1 watt. If your modulation spreads the power evenly over 50kHz, you could transmit 0.1 watts (+20dBm). If your modulation spreads the power evenly over 5kHz, you could transmit 0.01 watts (+10dBm). It _appears_ that you could transmit +8dBm (6.something milliwatts) however you want in that band: as an unmodulated carrier, or spread however you want. I don't suppose they talk about the time period over which you measure the spectral power density...but they probably wouldn't like it if you transmitte 1 watt that swept linearly and slowly across the 500kHz, say once a minute. Over a long enough period, that would be uniform power per unit bandwidth, but a one second snapshot would show 1 watt in 500kHz/60 = 8.3kHz bandwidth. Hope that makes sense. Beyond that--see your lawyer! ;-) Cheers, Tom |
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