By far the friendliest and most generous Part 15 Rule is this one
§ 15.23 Home-built devices. (a) Equipment authorization is not required for devices that are not marketed, are not constructed from a kit, and are built in quantities of five or less for personal use. (b) It is recognized that the individual builder of home-built equipment may not possess the means to perform the measurements for determining compliance with the regulations. In this case, the builder is expected to employ good engineering practices to meet the specified technical standards to the greatest extent practicable. The provisions of § 15.5 apply to this equipment.
The only member I know who has designed and built his own part 15 transmitter is Neil, Radio8Z, unless you count the committee of ALPB Members who designed the Big Talker shortwave transmitter.
I like Part 15.23. It reads so friendly!
Just do the best you can to stay within the guidelines because they acknowledge they realize most people can't. If your station inadvertently causes interference, a friendly Commission associate will advise you to please turn off your device until you have corrected the problem.
No threatening language, no intimidating reference to severe penalties. It all sounds so - accommodating. And bonus-equipment designed and built by the user!
Wait a minute, which rule applies to determine how the signal is regulated; by input power, by field strength, and what about the antenna. It says Part 15.5 applies to "Home-Built" equipment but that states nothing about the signal, only that you don't own any frequency, can't cause interference and must shut down if you do.
I suppose Part 15.209 would take precedence unless you can show your "Home-Built" meets other specific rules such as Part 15.219.
I need to lawyer up...
It's strange that there are no fcc-savvy attorneys on the part 15 forums. We have experienced RF radio engineers, but never a lawyer.
I am a Sea Lawyer. Does that count?
We would need to get our boats into salt water for you to have jurisdiction, John.
Here is the FCC definition of input power for AM broadcast transmitters using the "indirect method." The indirect method is the technique provided by the manufacturers of Part 15 AM transmitters to calculate the input power permitted by §15.219(a).
§ 73.51 (e) The antenna input power is determined indirectly by applying an appropriate factor to the input power to the last radio-frequency power amplifier stage of the transmitter, using the following formula:
Where:
Antenna input power = Ep × Ip × F
Ep=DC input voltage of final radio stage.
Ip=Total DC input current of final radio stage
F= Efficiency factor
The references there are to the d-c voltage and direct current present at the output electrode(s) of the final r-f amplifier in the transmitter -- not the r-f power applied to the input electrode(s) of the final r-f amplifier.
The "Indirect Method" in 73.51 is a useful piece of information to keep in the "Rules Folder," but does nothing to address my original question as to why 15.219 mentions filaments.
The "Indirect Method" deals entirely with DC voltage/current, while filaments are ordinarilly AC.
for the comments, Rich and Carl.
Carl, I'll try to give my take on the filament power being excluded. Remember that the intent of the rules is to limit the field strength radiated which can be done by limiting the power delivered to the antenna system. To do so and to make measurement easier 15.219 limits the "total" power into the final stage exclusive of the filament power which has the effect of limiting the radiated power. This is because the filament power does not add any power to the transmitter output and it need not be limited.
Neil
I added a reply here about an hour ago, but I don't see it now. I'll repost.
Rich, your suggestion of a re-write of 15.219 aimed at hobbyists is brilliant, and I encourage you to compose and submit a proposed draft of such.
And Neil wrote:
"This is because the filament power does not add any power to the transmitter output and it need not be limited."
True and that's what I thought in the first place, therefore what's the point of the FCC inserting the mention of filaments?
How about the grid drive? That's power input isn't it?
Personally I don't see the problem...input power to 'the final stage' of the TX (ATU etc.) is limited to 100mw...end of story there. IMO how much power you apply to tube grids or anything else is non-sequitur. The trick is to make that hold through to the antenna best as can be done, meaning the signal needs to be rock solid stable, which denotes overall efficiency. Only then can we really see how efficient the radiator/ground system is. BTW, I really miss having a ground in the boat, and the whole ocean for counterpoise. Creating artificial ground on this ol' rock is a PITA.
Looking for "grid drive" on Wikipedia, it asked, "Do you mean Grand Drive?"
So I looked in the ARRL Handbook and there are some grid-drive circuits, and I would think the "grid drive" might be the point of my way of seeing the issue.
The more overall voltage and current measurement of the final RF amp gives the character of the entire transistor, including input and everything.
But the rule only refers to input, which I take to be the "grid drive" coming from the preceeding stage.
And, with tubes, why would "grid drive" warrant mentioning filaments?
After this I'm going to give up and consider my question unanswered.
... IMO how much power you apply to tube grids or anything else is non-sequitur. The trick is to make that hold through to the antenna best as can be done ...
Just to note that the r-f power applied to the input terminal(s) of Class C/D/E final r-f amplifier(s) of an AM transmitter is not conserved or held through so as to appear at the output terminal of that transmitter.
The r-f power applied to such input terminals is dissipated within the final r-f stage, itself.
The maximum r-f power available at the output terminal of such transmitters into a Z-matched load is related only to the d-c voltage, direct current, and d-c input to r-f output conversion efficiency of the output electrodes(s) and components of the final r-f stage(s) of that transmitter.
Our good member Rich(F) earlier posted that FCC 15.219 could be re-written so to be better understood by less technical users.
I invited Mr. Rich(F) to compose and present an example of a better written rule for the benefit of the less schooled.
Why is it that I never expect this to happen?
Yeah thanks, you're right, but are we saying we can add more RF power in the final? Seems like a delicate balance else we violate the rule.
There are some decent tube AM transmitter kits and circuits available to play with:
http://www.ontheair3.com/index3.html (out of stock darn it! I was seriously considering it)
http://www.vcomp.co.uk/iTx/iTx_Kit.htm
http://electronbunker.ca/AM_StereoXMTR.html
http://www.dogstar.dantimax.dk/tubestuf/amtx-3.htm
%3Bhttp%253A%252F%252Fwww.electronixandmore.com%252Fprojects%252Famxmitter%252Findex.html%3B505%3B272
...there's more, too.