Total posts : 45366
The “nanowatts” you mention is the amount of RF energy radiated by the antenna conductor. The power level I mention is the transmitter final PA input power. They are different; quite different.
The use of a lossy antenna would allow 10 to 25 milliwatts of transmitter input power to produce the appropriate power for legal field strength. The whole theory behind the Part 15 rules is to control field strength with the use of lossy antennas.
FCC certification does NOT ensure legal operation either. Just ask the folks at Ramsey Electronics. They are unable to certify their Fm-30 transmitters now, after some folks decided to buy export transmitters and blame the manufacturer for their misuse. That’s like blaming auto manufacturers for the irresponsible use by a driver of their make of car. If you talk with Keith Hamilton (one of the good guys) about violating the letter of the rules with a Rangemaster transmitter, he will tell you they can be operated outside the rules and regs. Part 15 certification of hobby broadcast transmitters falls under the same set of rules as ALL other Part 15 devices. The Part 15 enforcement log includes plenty of entries for interference produced and operating outside the rules by all kinds “certified” Part 15 devices.
Regarding the isotropic antenna. You are exactly on target. There are no real-world isotropic antennas. But theoretical gain, at least in popular publications on the subject, puts the gain figure of a dipole at 2.26 db gain over that of an isotropic antenna.
That would make the gain of a 1/4 wave and the theoretical isotropic very close to one another, with the 1/4 wave system winning out due to non-linearity in the radiation pattern. AM broadcast rules have used this thumbnail comparison for over 50 years.
Your text books may not use the same figures or definitions, but broadcast engineering practice for the past half century certainly has. And as far as I know, no major university in my part of the world even have qualified professors to teach broadcast RF practice. That is not to mention the new crop of broadcast engineers who are very good in digital communications techniques, but digital communications do not require the sensitivity of impedance matching required by the electronics of yesteryear. I have taught such courses at a four year university at the invitation of the Department Head, mostly because they have no experience in the field. Some things you can book learn, some things must be learned by doing.
But, I digress. Sorry. The fundamental question remains how do uneducated everyday hobbyists stay comfortably inside the boundaries of the current Part 15 rules and regulations?
I have asked this question on several boards and groups, and as yet no one has been able to offer a satisfactory fool proof solution or answer. Until someone does, the FCC will continue to apply the rules based on the personal interpretation of individual inspectors. The rule of law works poorly in that environment. The first time you get bit by that kind of legal system, I suspect you won’t like it. I know I don’t.
The original forum topic deals with the FCC enforcement of the current version of Part 15 regulations dealing specifically with part 15 broadcasting. And I hope you would agree, the Part 15 rules dealing with hobby broadcasting are sadly lacking. So, has anyone been sent a letter or been visited by the FCC for a violation of Part 15? My money is on, “there will be few takers.”
Marshall Johnson, Sr.
Rhema Radio – The Word In Worship