Historically these rules were based on power measuring technologies like bolometers which are light bulbs in a wheatstone bridge.
The bolometer would measure DC-8 GHz for example. Oblivious to frequencies of any carriers present. They all contributed to the heating of the filament. Total power. If all that power was put into a CW carrier, that is quite a bit of power density. So a rule like: (A) The average equivalent isotropically radiated power (EIRP) must not exceed 2,000 watts within any 5 megahertz of authorized bandwidth and must not exceed 400 watts within any 1 megahertz of authorized bandwidth. You can see that if there were 5 channels, each 1 MHz wide, each producing 400 watts, and each terminating in a dummy load in a bucket of water, that water would get just as hot as if there was one transmitter with a 5 MHz channel pumping out 2000 watts. From: Forrest Christian (List Account) Sent: Thursday, June 16, 2016 8:18 AM To: af Subject: [AFMUG] Power limits per hertz. I've had a couple of conversations over the past little bit which has gotten me thinking about power limits in relation to channel width. This is my thinking. Assume 5.8ghz, ap side. Power limit 36dbm. My question/thought/potential misunderstanding has to do with how that 36dbm is measured. Assuming you're comparing a 20 mhz channel with a 10 mhz channel, both at EIRP limits, does the 10 mhz channel effectively have more Power density? Assuming this is the case, it seems you would gain 3db of link margin for the increased power density and 3db more for reduced noise floor. 6db is double the distance which is big, even with the reduced throughput. Is this the way this works?
