Posted by John Davis on August 24, 2024 at 18:54:52.

In Reply to: Re: Abby update and frequency change posted by Steve on August 23, 2024 at 20:22:15.

I endorse and have used W1TAG's method myself. It provides a useful and generally supportable first approximation of field intensity, provided through the exact same engineering methodology used to calculate TV and FM coverage areas, for instance. In the professional case, the antenna gain factors are more accurately measured beforehand, of course; but the dipole and monopole assumed free-space values are close enough because ground losses in this band are so high that reflected signals from the earth are not as significant as they would be at lower HF frequencies. Nowadays I am fortunate enough to own a calibrated measurement loop and have access to both a frequency selective RF voltmeter and a calibrated spectrum analyzer. So, if I am still able to get around for a while longer, I should be able to perform actual field strength measurements on my anticipated new station. But what I'd also LIKE to do, if possible, is to determine real-world pattern gain values on a variety of antennas of different types, located at various heights over ground. I have just one minor quibble with John A's article, and that is the sentence, "The FCC rule is really aimed at ISM users who generate large amounts of power in confined areas." The rules pertaining to ISM gear are in Part 18. ISM gear is explicitly exempt from in-band radiation limits! The Part 15 general limits do apply to ISM outside the designated bands, not within. But ISM is also not allowed to transmit any form of intelligence. Part 15 short-range devices are exactly the opposite: limited radiation, but no restrictions on modulation (other than still keeping emissions in band, of course). Since radiated power is wasted power as far as ISM equipment goes, manufacturers generally do a good job of confining it. Even so, what does manage to escape is the major source of the never-ending racket at mid-band.

Follow Ups: