The Part 15 Rules as they are written are sketchy. As such, I believe the Rules therefore allow certain creative interpretation.
The Part 15 Rules as they are written are sketchy. As such, I believe the Rules therefore allow certain creative interpretation.
I believe 15.219, defining the conditions for AM broadcast, are in fact an “ideal situation sketch”, describing the circumstances at high sun during a day.
Because the FCC Rules are based in mathematical logic, we can therefore extrapolate what other meanings might be inferred based more on the poetics of living in a changing world, where night is significantly different than day.
It is my judgement, sitting upon the seat of transcendental oversight, that a Part 15 AM station is (by silent implication) allowed to boost power so as to always equal the signal coverage of that perfect mid-day model.
Next question is, what “input power to the final stage” will it take to replicate daytime performance?
Day/Night
My first thought is the huge difference in the band conditions between the two time point references, and the bands constant fluctuation in between. A field strength and time line chart would have to be created for various environment conditions and combinations to develop some kind of base line reference as to input power to compensate.
Sounds like a new LPAM service is needed. 🙂
RFB
And Furthermore
Of course nighttime signal can also be enhanced by having an antenna that is able to extend somewhat beyond the 3-meter mid-day length, or a special nighttime antenna that can be switched in at sunset.
As RFB mentions, the conditions fluctuate a lot from the mid-day ideal, but for rough settings we can use an estimated “worst case” middle of the night condition. This might give us the outer boundaries of the needed signal enhancement so that coverage in the dark would (somewhat) equal coverage in the light.
A transmitter that could be self-setting and ride its own settings so as to track the changing conditions might be a little bit too sophisticated but is not beyond reason.
Idle Speculation
This is only, of course, idle speculation, about the wilderness known as nighttime on the AM band, and the only true way to arrive at approximate numbers would be trials and tests comparing night coverage to day.
But let’s just double everything for the sake of conversation.
Sun goes down, input to the final jumps up to 200milliWatts, antenna is extended to 20-feet.
I’m thinking that wouldn’t be enough to come close to matching daytime coverage.
Should work OK
“I’m thinking that wouldn’t be enough to come close to matching daytime coverage.”
Well, really poor atmospheric conditions notwithstanding, I think that should work. You could use a X10 timed antenna switcher, and a secondary TX amp, or just another TX.
Also, precise tuning is a factor.
Now, I’m wondering if I can hook up a RF field strength meter to the computer using O-scope software, with an output connected to a shielded step-motorized vernier geared aircap. Sit inside and watch the screen show you the precise tuning.
If it could be done at reasonable cost, you could even do it remotely from anywhere, with a computer, iPhone, iPad, etc.
Remote All the Way
As this whole maze gets put together the idea of remote everything is very attractive. Keep thinking about ways of measuring field strength remotely. That could make for a very interesting system.
Change
“Sun goes down, input to the final jumps up to 200milliWatts, antenna is extended to 20-feet.”
I think the limits should just be raised to 20 foot antenna, no ridiculous feed line garbage, 250mW RMS/1W PEP and be done with it.
RFB