I ran into MICRO1700 at a laundromat and we got to talking.
MICRO had an idea I've never thought of for Part 15 FM stations used as Studio-Transmitter-Links (STL), but otherwise do not want to attract too much attention in their signal range.
The secret: use in-between channels!
I tried it. It works. I moved from 89.5 to 89.6 and am now "off the dial" for anyone flipping to ordinary digital channels, but my digital radios are capable of tuning the in-betweens and of course analog receivers can do it.
The one thing that needs checking is that I want to move AWAY from any nearby stations and not TOWARD them.
Part 15 is fun all over again.
The allowed coverage on 13.560 mHz also makes for a fantastic STL.
Yes, Retro Radio, 13.560 is very prime for STL use.
My SW transmitter does AM but it could be re-designed to broadcast FM for possibly better frequency response...
Question is, how can FM be received on a shortwave frequency?
Your shortwave receiver would need at least two things: An IF frequency response wide enough to accommodate your FM signal and an FM detector such as a ratio detector or discriminator.
Perhaps an SDR radio could be programmed to do this.
Another way to demodulate an FM signal with an AM receiver is "slope detection." This is when you tune off center from the carrier. The amplitude of the received signal would vary as the signal swings above and below the frequency to which the radio is tuned.
Not the best way to demodulate FM but could work if the IF is wide enough or the FM deviation is small enough.
how many remember this little gem from way back?
http://web.archive.org/web/20001210162100/http://www.casinocom.com/slater/numaxnet.html
it used a 13.560 mhz (15.225) STL transmitter to feed solar powered roadside 15.239 fm repeaters
There is no intrinsic limit to the audio frequency response of AM or any other modulation method. The limitations we live with are due to the available bandwidth the FCC allocates for the respective broadcast bands.
As an example, the measured audio frequency response of my solid state AM transmitter is 20 to 17,000 Hz (3 dB down points). The audio sounds very good on various AM receivers around here but it really demonstrates the capability of AM when received with the BC-1004-C receiver which has a wide IF bandwidth. It sounds as good as an FM signal.
In fact, FM audio is limited to 15 kHz because of the presence of the 19 kHz pilot whereas AM operating under Part 15 rules has no such limit. The upper limits on audio frequency for both licensed broadcast AM and broadcast FM result from the FCC rules for each service.
Neil
The shortwave bandwidth allowed per 15.225(a) extends from 13.553-13.567 MHz, amounting to 14 kHz.
As we understand it, the audio frequency response will be 1/2 of this bandwidth, amounting to 7 kHz.
Carl, as you wrote this would limit the highest audio frequency to 7 kHz. Though not "FM quality" this would likely be adequate for an AM STL.
Neil
Of course all of us, and we, are pleased to know we can legally transmit greater than 7 kHz bandwidth per 15.225.
"We" in my use refers to the class of persons interested in the subject.
Maybe Artisan can correct me but BETS-1 says you must be on a frequency that is allocated for broadcast and not "off" it....Artisan?
Even on a car radio which is the most selective that you can get there will be some spill over of signal on strong stations onto a .1 mhz ajacent. On a home radio worse. Also your station in close proximity to the transmitter could interfere with a station on it's proper place if yours is just off to the side, not the .2 mhz it should be.
Mark
Mr Blare writes: Of course all of us ... are pleased to know we can legally transmit greater than 7 kHz bandwidth per 15.225.
However that fact would not be "News" to those who researched and fully understood all of FCC §15.225 before they posted conclusions that §15.225 does not support.
FCC 15.239 (a) Emissions from the intentional radiator shall be confined within a band 200 kHz wide centered on the operating frequency. The 200 kHz band shall lie wholly within the frequency range of 88-108 MHz.
I recall this being discussed before, and the consensus seems to be that part 15 operators are not confined to allocated frequencies.
Part 15 certified transmitters can be set to in-between channels and FM digital radios are able to select the odd channels.
Post # 12 note from the teacher: "However that fact would not be "News" to those who researched and fully understood all of FCC §15.225 before they posted conclusions that §15.225 does not support."
You can't flunk me now this is spring break.
Mr Blare wrote: You can't flunk me now this is spring break.
Attempted or even true humor does not overcome fact.
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 or was evaluated?
Per Mr Blare: The shortwave bandwidth allowed per 15.225(a) extends from 13.553-13.567 MHz, amounting to 14 kHz. As we understand it, the audio frequency response will be 1/2 of this bandwidth, amounting to 7 kHz.
Who is "we?"
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.
See below:
§ 15.225 Operation within the band 13.110-14.010 MHz.
(a) The field strength of any emissions within the band 13.553-13.567 MHz shall not exceed 15,848 microvolts/meter at 30 meters.
(b) Within the bands 13.410-13.553 MHz and 13.567-13.710 MHz, the field strength of any emissions shall not exceed 334 microvolts/meter at 30 meters.
(c) Within the bands 13.110-13.410 MHz and 13.710-14.010 MHz the field strength of any emissions shall not exceed 106 microvolts/meter at 30 meters.
(d) The field strength of any emissions appearing outside of the 13.110-14.010 MHz band shall not exceed the general radiated emission limits in § 15.209. //