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“Experimental radio” is a broad term that might encompass programming, advertising, or technical trial and error tests.
Specifically as a technical term relating to RF (radio frequency) experimentation, one use of Part 15 is precisely that… experimenting with power, range, modulation… except for one limitation:
As we understand it today the field strength/power/antenna limits specified in Part 15 cannot be legally exceeded.
At one time there was a rule contained within the Part 15 section describing a procedure for experimenting beyond the normal limitations, but that rule is now labeled RESERVED and is no longer in print.
Another section of the FCC Rules contains the title “Experimental Radio”, but going there one finds within the text no reference to what “experimental radio” is or how to apply for it.
Yet we notice in various radio news accounts stories about experiments outside normal boundaries that are taking place, such as the stations testing All Digital AM.
This topic has risen before, but we ended up stumped and learned nothing new.
Let this be a call for input on this subject… what steps are available to apply for experimental status?
Total posts : 45366Carl wonders “Let this be a call for input on this subject… what steps are available to apply for experimental status?”
Part 15 of the rules used to have language which detailed the procedure for applying for FCC authorization for experimental use of radio transmissions. Going from memory, application was made to the Chief Engineer of the FCC District in which the transmission was proposed and required the specification of a very limited time schedule for operation. Presently, the Part 15 Rules do not include this information but does this rule out approaching the Chief Engineer for exemption? I do not know, but I did look into this in the early 70s when I had an application for using radio telemetry in medical research and was informed by a FCC representative that I could apply for exemption but that these were seldom granted. I found another way to provide a signal link.
Experimentation on the broadcast bands with Part 15 compliant transmitters is possible since under the rules modulation methods are not restricted (except damped waves) and can be done without increasing power or out of band emissions beyond the limits. Be mindful that such experimental modulation methods would not be of use in broadcasting since normal AM and FM receivers would not properly receive such signals.
We could try SSB or digital modulation methods using Part 15 devices on the broadcast bands but these wouldn’t benefit broadcasting. Some low data rate methods can be used to extend the range of the signal but not for reception on conventional receivers. This experimenting could be fun but today’s off the shelf Wi-Fi and Bluetooth equipment gives much better performance so I can’t imagine myself doing any such “experimenting” on the broadcast bands. Others might be interested in ultra low rate CW, etc. and that is fine.
I am not qualified to speak about experimentation carried out by licensed services but my impression is that it is possible to get exemptions for this. The evolution of cell phone services would not be possible if this were not the case.
Neil
Total posts : 45366What about experimenting with FM modulation on AM. It would certainly have to be narrow band FM because wide band FM would take up too much bandwidth.
Thinking of how narrow band FM would cause the audio bandwidth to suffer in sound quality as normally it would be more suitable for two way communications and therefore could cause music to suffer, a sort of processing method would have to be applied at the receive end. However for this to work there would have to be some sort of way to tell the receiver to peak up certain frequencies in the audio spectrum at precisely to right time in milliseconds. Sort of how Dolby Pro Logic works only this would be simply to compensate for the narrow banding of an FM signal.
Coming up with a method like this could at least lower the noise floor for that ban and make your signal more listenable. The only problem with this is that current AM receivers would have to be modified with slope detection.
Any thoughts on this technology?
Total posts : 45366TheLegacy asked: “What about experimenting with FM modulation on AM?“
We understand what TheLegacy is asking, but the language isn’t exactly accurate.
What he means is “What about experimenting with FM modulation on the medium wave band (MW) (?)”
This question was already answered by Neil up above who mentioned what the Part 15 rules say about modulation: “Experimentation on the broadcast bands with Part 15 compliant transmitters is possible since under the rules modulation methods are not restricted (except damped waves)“
TheLegacy is correct that very narrow band FM would be required to match the relatively narrow (10 kHz) bandwidth of the channel allotments on MW.
Speaking for myself now, I remind readers that, as TheLegacy says, using FM on MW would require modifying the radio accordingly, because an AM radio would not detect an FM signal.
Therefore we ask the question, why experiment with FM on MW? What is the experimentor hoping to find?
Total posts : 45366If anyone wants to know what NBFM sounds like listen to any 2 meter repeater.
Total posts : 45366what about Supressed Carrier AM? the average AM power input is below 100mW inout but modulation peaks can far exceed 15.219 input power while the avarage power input is below 100mW input to final. i wonder how this type of system would work in tandem with class E and a high efficiency loading coil and monopole system.
Total posts : 45366Wouldn’t suppressed carrier am give an affect like PEP as far as the power? Almost like those Radio Shack CB walkie talkies that use it? wasn’t sideband but it was suppressed carrier AM or double side band. what would music sound like using suppressed carrier am? how much would that how much would that improve range?
Total posts : 45366Double sideband suppressed carrier transmission would cause problems with demodulation in so far as a receiver bfo (which mimmicks the tx carrier frequency), would have to be the exact frequency to demodulate the audio correct frequency response wise (pitch).
And dssc would cause lots of distortion of a normal envelope detectorThis is why exhalted carrier, or reduced carrier is used for a synchronous demodulator, the sync demod is able to be phase locked to the reduced carrier.
This technique is used for the 90 degree phase demodulation in c-quam audio recovery of the L-R audio, as it has to stay locked to the carrier and still demodulate properly when the transmitter is under negative am modulation of the transmitter.
Paul.
Total posts : 45366Not mentioned so far is the fertile business of experimenting with antenna variations, looking for antennas that radiate more of the RF energy produced at the output of the transmitter.
Station8 is presently developing several novel twists on conventional AM antennas and reports good results so far.
Much has been said in previous threads about the quest for more efficient loading coils, which are a part of the antenna system.
Part 15 Engineer points out the efficiency advantage of Class E RF outputs such as the AMT5000 from SSTran.com, a must have for any operator who wants the most from his 15.219 system.
TheLegacy and other experimentors report of “taking drives” to test the range of different antenna combinations, but I have found a more convenient way of testing antenna performance without ever starting the car.
By reducing the output of the AMT5000 to minimum (34 mW to the final RF stage) the differences between antennas can be demonstrated within an ordinary household without needing to go out the door.
Antenna efficiency for FM might improve multi-path and standing wave characteristics, but 15.239 is capped by field-strength at 3-meters leaving no room to enlarge the range.
As I continue to say, the mini-allowance of 15.239 seems to me arbitrarily lower than necessary, and I would further state that elasticity of FM field strength should be calcuable for diffierent geographic locations.
Whereas I believe 15.219 to be intelligently derived by RF engineering, it would appear that 15.239 has earmarks of lazy legal short-cutting.
The FCC serves as public trustees, we are the public, and kindly implore the FCC revisit 15.239 and put it to the engineering staff for a more attentive and reasoned outcome.
Total posts : 45366wdx said: If anyone wants to know what NBFM sounds like listen to any 2 meter repeater.
I havent listened/talked on 2 meters since about 1978, but recall it to be clear, strong, and intereference free.
Total posts : 45366I was refering to music quality.
Total posts : 45366The 2 Meters of the 70s is vastly different than today’s 2 meter band, notably that it used to be wideband FM.
At anyrate, FM takes a LOT more signal to decode than AM. AM is likely the most robust transmission system that carries quality audio. SSB CAN sound quite good with music, though getting the BFO right is extremely difficult.
Narrowband FM is plauged with problems especially when the signal gets weak, public safety HATES narrowbanding.
Carl mentioned multi-path, the biggest cure for that is either killing the stereo pilot or getting the antenna up above all obstructions.
Total posts : 45366Since multi-path is “multi” path, kindly explain to me how killing the stereo pilot affects signals coming from multiple directions?
Total posts : 45366“Since multi-path is “multi” path, kindly explain to me how killing the stereo pilot affects signals coming from multiple directions?”
Killing the stereo pilot helps reduce the noise caused by multipath.
Total posts : 45366You know, that irritating popping in and out of the stereo component.
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