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## Re: [TowerTalk] RF Pattern

 To: Re: [TowerTalk] RF Pattern "K8RI on Tower talk" Thu, 27 Apr 2006 16:41:02 -0400
 > The RF patterns (for safety) discussion is interesting. What seems to be > missing in much of the discussion is a definition of "average power". How > is this determined? For example, if I am a "hunt and pounce" CW DXer who http://n5xu.ae.utexas.edu/rfsafety/power.shtml gives a good explanation and examples. It's pretty straight forward. It's based on a 30 minute period over an uncontrolled area and 6 minutes over a controlled area. > transmits less than 1% of my operational time --- but might hit 20% for > short periods in a pileup ---- how do I use the formulas and compute You use 30 minute and 6 minute periods where you transmit the most. First you take the duty factor which is 40% for CW, 20% for SSB and 100% for FM, RTTY/Digital/ and AM. Calculate how much time you are transmitting during your busiest period and calculate the average transmit time for both 30 minutes and 6 minutes. Multiply the results by the duty factor. > "average power"? Is "average power" computed the same way for controlled > and uncontrolled areas? If my operational time varies from 0 to maybe 2 Average is average, but the times are different. > hours a day---with a long term average of 30 minutes a day---how is this > averaged for these computations? It doesn't matter how much you are on during any particular day. The only periods used ate the busiest 30 minutes and the busiest 6 minutes (periods with the most transmit time. > > I assume that actual CW transmission might have 50% average key-down power > and SSB somewhat less. 40 and 20% respectively. Multiply the average transmit times to get the average power. For an example on FM. You are running 300 watts, you transmit 2 minutes, listen 2 minutes and transmit for another 2 minutes. So your average is 66.66... or just round to 67%. So your average transmit time is 67% and on FM the duty cycle is 100% * 67% * 300 watts = an average of 201 watts. or take 1500 watts of SSB with a 20% duty cycle. Chasing DX you are going to be transmitting less and listening more. So say you only transmit 2 minutes total out of 6. That is 33.333, or 34% rounded up. That makes 20% * 34% * 1500 for an average of only 102 watts. > > For operators in my general category, where the long-term transmitting Long term does not enter into the calcs. > average time is a few minutes per day (CW or SSB) it would seem that these > averages will dominate any of the exposure computations. Really heavy use > of RTTY, FM, etc, is a completely different matter and would appear to be > so different that they should be computed differently. For my type of You use the duty factor for these which is 100%, but the transmit time is still the average for the busiest 30 minute and 6 minute times. > operation, it would seem that (provided someone does not lean his head > against the center of a beam or dipole) any reasonable operation is safe, > even with a KW transmitter. > > Am I way off the mark here? Not too far Good Luck, Roger Halstead (K8RI and ARRL 40 year Life Member) N833R - World's oldest Debonair CD-2 www.rogerhalstead.com > > Bill - W2WO > > _______________________________________________ > > > > _______________________________________________ > TowerTalk mailing list > TowerTalk@contesting.com > http://lists.contesting.com/mailman/listinfo/towertalk > _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk
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