Rich challenged us: "Wouldn't you agree that your post about the 7 kHz audio bandwidth permitted to legal, unlicensed SW stations under FCC §15.225 was incorrect, no matter when it appeared?"
No, I wouldn't agree.
As a face-saving gesture toward you on this easter basket we allowed that the claims made in your Post # 9 were correct.
The fact is, your exhibits shown in Post # 9 in no way prove that a frequency at 13.560 MHz would be allowed the unstated wide bandwidth you infer.
In his Post # 8 Neil Radio8Z found no fault with my bandwidth math, he verified it.
Let it be noted that you are not nipping at Niel's heels over this made up confrontation.
Mr Blare wrote:
...we allowed that the claims made in your Post # 9 were correct.
Then he wrote in that reply:
The fact is, your exhibits shown in Post # 9 in no way prove that a frequency at 13.560 MHz would be allowed the unstated wide bandwidth you infer.
If you can, Mr Blare, kindly post the technical justification for your opposite conclusions about Reply 9, which I quoted above.
He posted: "If you can, kindly post the technical justification for your opposite conclusions about Reply 9, which I quoted above."
I would, except your challenge is 180-degrees out-of-phase with anything to do with the discussion to date.
My only "conclusion" wasn't a conclusion; it was an observation.
My observation wasn't "opposite" anything you'd posted, since what you posted doesn't demonstrate what you claim it does.
Shall I repeat myself a few more times, given that my original posts were quite clear and on point(?)
Mr Blare wrote: ... your challenge is 180-degrees out-of-phase with anything to do with the discussion to date. ...
Posting so does not prove so, as probably most readers of this thread will recognize.
People who support, thoroughly research/understand, and post provable fact rather than opinion and bluster are much more likely to be believed.
Preaching is not a conversation.
You can believe me on that.
So Rich, it seems what you infer is the carrier can be at the maximum allowed field strength within the 14 KHz centered on 13.560 and the sidebands due to modulation don't really count since that energy is intermittent and it's average value would be at or below the field strength allowed outside of the 14 KHz centered on 13.560 KHz?
Therefore, operate with a maximum carrier field strength as allowed at 13.560 KHz and use full audio bandwidth since the sidebands average value outside the 14 KHz centered on 13.560 KHz would likely be at or below the allowed field strength allowed outside that 14 KHz window?
For as you stated above:
"Note that FCC §15.225(b)(c)&(d) permit legal emissions above and below 13.553 and 13.567 MHz, which enable the transmission of DSB (A3A) AM sidebands from such unlicensed systems having audio bandwidths greater than 7 kHz."
FCC §15.225(b) permits an r-f field that is 33.5 dB below the field of the AM carrier, within the bands 13.410-13.553 MHz and 13.567-13.710 MHz. So the total r-f spectrum available for AM sidebands is 300 kHz, albeit only the 14 kHz r-f bandwidth centered at 13.560 MHz would permit 100% modulation of the transmitter.
But this doesn't mean that a brick-wall audio filter is needed. The spectrum of music and speech contains much less energy at audio frequencies above 7 kHz than below 7 kHz.
The clip below shows the audio spectrum of a classical music recording of a symphony orchestra and chorus. Even though it has components extending past 18 kHz, the energy above 7 kHz is considerably less than below 7 kHz.
As 100% modulation of an AM transmitter produces sidebands that are 6 dB below the unmodulated carrier, that means that the the upper and lower sidebands produced by the audio spectrum above 7 kHz must be attenuated by 27.5 dB in order to comply with §15.225(b).
But that relationship already is met with most audio sources, so there wouldn't necessarily be a need to limit program audio to 7 kHz.
Of course all of us are pleased to know we can legally transmit greater than 7 kHz bandwidth per 15.225.
Thanks Rich. I think that cleared it up.
We agree with MRAM, the matter has been cleared up and something mentionable has been learned in this thread...
There are (sometimes) different ways of interpreting the FCC rules, as in this case I perceived 15.225 (a) through (d) as being EITHER/OR choices for legal operation. In otherwords, what I saw was that one could EITHER use (a) OR (b) OR (c) OR (d), and I happened to choose (a) for my bandwidth calculation.
What Rich presented was a way of COMBINING (a), (b), (c), and (d) as a means of legally achieving a much wider audio bandwidth. That is to say, he posed a AND proposition, as in (a) AND (b) AND (c) AND (d).
Bookmark this lesson.
Thanks for posting so, Mr Blare.
There is a difference between what is legal and what is practicing good operating and engineering skills. What do I mean by this you ask? Read on below please:
For FM the FCC has allocated frequencies to end at the odd decimal point for example 88.1,88.3, 88.5, 88.9 Mhz. Well this is true you could transmit on 88.0 Mhz to try and avoid interference in your area during times where NO DUCTING is occurring I believe that if everyone would do this it could cause issues during different times of day or seasons of the year. And this is why.
Your transmitting right along on 88.0 Mhz and all of a sudden after 6PM your area is under a temperature inversion (causing a ducting effect). Your neighbot likes to listen to that NPR station that only comes in during times of ducting. They are happily listening while walking or even driving through your apartment complex and when they get near your transmitter they hear chchcsssvvv vvv vvv crackle crackle when they pass your house for more than 200 feet. If they hear your voice they'll know its you and they may make a complaint to the FCC.
It is my belief that the FCC mae a major mistake allowing part 15 FM broadcasters to operate on .2, .4, .6, .8 of a frequency and in fact if our initiative petition goes through I'm willing to work on abolishing the legality of broadcasting on in between frequencies because of this. I also believe this was another reason that FM broadcasters complained about part 15 FM years ago.
As micro broadcasters we have a responsibility to operate with good practice and the broadcasting on in between frequencies is a very bad idea and shows non compliance to the respect of uniformed broadcasting standards and causes interference to adjacent stations.
Please use the legal frequencies of the odd numbers after the decimal point.
Here's what I tested after my first post in this thread.
I put my transmitter on 90.0 Mhz and tuned the FM radio to that channel, with good results.
But I noticed that my signal could also be heard at 89.9 and 90.1, so it wasn't hidden in any way.
I came to the conclusion that nothing is achieved by using those in-between channels, and I tuned back onto ordinary channels.
The Part 15 way is to try something, and if it works, fine, if it doesn't work, stop doing it.
Legacy that is a very bad idea, please don't try that.
I can agree if you want to be heard stick to the band plan, if not then it doesn't matter.
FWIW Coming from a commercial broadcaster's view point, nobody listens to stations they don't normally recieve. No ordinary listener will put up with that weak of a signal, additionally the station itself does not care about that listener. The listener is outside of their area and does nothing for their ratings or ad dollars. The FCC does not protect signals beyond their 60dbu aside from spacing restrictions, unless sufficient complaints from a LARGE number of listeners are recived due to an LPFM or translator. Furthermore part 15 devices on the FM band do NOT have enough power to overcome any measurable amount of skip. Any skip in the area will wipe out a part 15 transmitter. Any station operator should not (and does not) concern itself with skip, theres nothing they can do about it.
Mighty 1650 I may agree with some of what your saying but...
In Elizabeth City, NC where I lived with my Wife from 2007-this year. Every day during the warmer times of the month that country station came in on 96.3 FM at night and FULL QUIETING. Assuming your not one uV/M at 3 meters past what is allotted by the FCC (and we know not every transmitter sold is even if it claims part 15 certification) you can still cause a mess when this happens by not checking your frequency after 6PM. Im sticking to my guns on this one. In Michigan (Lansing that is) WHNN would come in nicely every summer and FULL quieting Stereo. Even the station iknew of it and served Lansing with some ads that mentioned Lansing. If you were to transmit on 96.1 during the times that the station is not receivable that is fine. What is an issue is when you continue to operate knowing that many folks loved Album Rock and you start playing Rap or Pop I'd complain right to the FCC. If that didn't do any good believe me as a Album Rocker I'd find a way to get you off the air because I want to listen to that station not your Rap crap.
Again we have a responsibility to see to it that we don't interfere with the respect of others who want to listen to their favorite station. Again as an unlicensed station YOU have NO RIGHT to jam another signal. That makes you a Johnny Punk if you do. I've made that term up and explained it and continue to do it on the Initiative site. Johnny Punks shall be delt with in the most harsh way possible. Again it is why I'm driving a hard force to stop the disrespectful operations of in between frequencies. If you don't want to be heard than buy a Bluetooth transmitter. FM is so that you can intentionally be heard on an orderly functional FM Radio.
You know there is all sorts of talk about what makes us different than a Pirate. Pirates don't care rather they interfere or not. By you jamming a strong likable skip station does that make you the same as a Pirate? Your not caring? I say it makes you the same as they are because your practicing poor engeneering and broadcasting judgement.
Lets practice good skills here. There is more at stake than 15:239.