Does the FCC have a requirement that mobile radios on a licensed frequency cannot continually broadcast, instead they must broadcast in short spurts? And, if there is such a FCC regulation, how can I find the actual document in which this appears?
Last, what is the purpose to this rule? Once assigned a frequency, why should the FCC really care how long my transmissions are? 
Under which part of the FCC rules in 47 CFR are you operating? Part 22 paging? Part 74 TV/Radio broadcast? Part 90 commercial radio? Part 97 amateur?
Depending on which part of the rules you’re licensed for, you may very well be able to continually transmit (broadcast is not the correct term) but without more relevant information about your license there is not much that can be done except speculate.
I suspect that this is, indeed true.
Since it’s very likely that no one else nearby can broadcast on the same frequency as you are using, the FCC would like to prevent you from hogging that frequency.
Finding the particular rule might be hard - it’s probably band dependent (for example, Cell phone, TV, radio and cordless phones all have different rules). What band are you thinking of?
There is such a rule, sort of, governing the use of the citizens’ band frequencies. As reported here, the use of CB frequencies is on a “take turn” basis. One station can broadcast to another for no more than 5 minutes at a time and must take a one minute break from communicating before making another transmission. My remembrance from my CB days in the 70’s is that this is because there are so many users on each frequency within short distances of each other. Being that the CB band is incapable of duplex operations (users can transmit signals simultaneously, much like people on cell phones can talk simultaneously and still hear each other), two or more users transmitting simultaneously on the same channel will cause unwanted heterodyning, or mixing of their frequencies, usually causing a squeal on the channel and preventing anyone else from using it properly
Of course, when I was on the CB back then, the owners of CB radios had to hold a license for their stations. That is not the case now, as the FCC no longer issues CB licenses and authority of operation is granted merely by owning a properly FCC certified piece of equipment.
CB licenses are issued by rule, not by application, and are not exclusive use. One does not obtain a license to use CB frequencies from the FCC.
Code of Federal Regulations Title 47 is where the relevant telecommunications rules are articulated.
Yes, I know. I don’t believe I said otherwise.
However, CB frequencies are still licensed to the public for personal use and the use of those frequencies is governed by the FCC, even if individual stations aren’t licensed. The “take turns” rule is still in effect for the CB frequencies. And Jinx did say “licensed frequency,” not “licensed radio station.”
It seems to me that, lacking other specifics, my answer is just as relevant to the question as any, pending the addition of more information.
Short answer: No, er, I, uhh, mean yes, er, uhh, the question can’t be answered with the info given.
Long answer: The FCC has so many services, on so many bands, for so many purposes, that if you have some legitimate reason for a continuous transmission, you will likely find some service and license category that will allow it. There are even frequencies that you can do that on (with low enough power) without any kind of license at all. Baby monitors are a good example of that. If you get a license for a service that assigns you an exclusive frequency, and allows continuous transmission, they have no problem with it. That’s what it was assigned for. On the other hand, many services do NOT assign an exclusive frequency, and you have to share, according to the rules of that service. Google GMRS (General Mobile Radio Service) for an example of non-exclusive licensing, and the rules for that service. Then Google FRS (Family Radio Service) for an example of a “no license” service that has similar rules (and some frequencies shared with GMRS). The question has no actual answer, unless you get alot more specific with your “hypotheticals”. What do you want to use it for? It makes a big difference in the service you will be licensed to use, and the rules you will be required to operate under.
The OP has to do with FCC rules for Mass Notification Systems (MNS) operating on a licensed frequency in the UHF or VHF bands. These systems often use a Motorola CDM750’s. The wattage of the transmitter is low, like 4W to 6W, max. Does this help any? (I wish I knew more how to answer yoru questions.) I have no idea what FCC reg’s apply to these systems. I wager if I did, then I would be one step closer to finding what I seek.
As for CB radio, I always thought CB’s operated on an unlicensed frequency as opposed to its licensed equivalent, the HAM radio. Is this not correct???
CB originally required a license obtained by paying a license fee. There is a limited set of channels (shared) and transmission types (am and ssb) and power. There is no longer a license required but the regulations are still there.
Ham radio was and still requires an operator license obtained by passing a test. You are limited to bands of frequencies (shared) and segments of those bands depending on your class of license. There are lots of rules and regulations,
I can’t find anything specific about MNS transmissions, but the FCC regulation that covers general licensed transmissions can be found here. Under this section, licensees are required to share their assigned frequencies; if they don’t, the FCC can require additional measures, such as restrictions on power or antenna height. The regulation doesn’t give a specific time limit, however and, as far as I can tell, there isn’t one as long as all parties share the frequency.
MsRobyn, WQKW259
MsRobyn, I am not sure what you mean by general licensed transmissions, since your cite is for GMRS. GMRS covers all of 8 frequency pairs out of more than 70MHz of spectrum, in other words less than 1/10 of 1% of the available spectrum.
With regard to OP, the only way a continuous transmission would be permitted would if you had an exclusive use license, which is doubtful given the power levels you’re running and the description of the system you’ve provided. Typically, exclusive use frequencies will be very hard to come by, especially in urban areas, and the only means of acquisition is on the open market… I have seen exclusive-use UHF frequency pairs go for over $500,000 in Los Angeles.
Since we have more information on OP’s situation, I will point him to 47 CFR Part 90.403, which states that “each licensee must restrict all transmissions to the minimum practical transmission time and must employ an efficient operating procedure designed to maximize the utilization of the spectrum.” Obviously, a continuous transmission will not be the minimum practical and does not lead to efficient use of the spectrum.
Note there is an exception for exclusive-use licenses.
I know my cite was for GMRS, which was the closest thing I could find since I couldn’t find anything specific for MNS. That’s all. 
Hmm, maybe I misunderstand what a license to operate entitles one to do. When you are granted approval to use a frequency by the FCC, are you saying that does not mean it is exclusive to you (within a given area limited by your transmitting wattage)? Are you saying one either has an “exclusive use license”, or one must share the frequency with others in one’s transmitting area?
Not that MNS needs to broadcast continuously, but sharing a frequency for mass notification just doesn’t sit right with me, either. An emergency message could be “walked-on” at any time! Does the FCC recognize other “usages” between exclusive-use and shared?
If you do not have an exclusive use license, you do have to share the frequency. There are certain courtesies that licenseholders extend to each other; these may be enforced by the FCC if need be. These include not stepping on each other’s transmissions.
When you’re talking about this MNS, are you talking about a system that uses a transmission to broadcast messages to people’s cell phones, or something similar?
with shared frequencies interfering with a transmission is against the rules. you need to check that the frequency is clear before starting your transmission.
this can be done with automated systems as well.
I looked up the Motorola CDM750 specs, and from what I can see, it works for a very large number of different services. It depends on the service you are using it with. I couldn’t find anything useful on MNS, so I can’t say about that particular use. Maybe a more complete description of what the MNS is, frequency it operates on, etc would help.
Yes, that’s exactly what I am saying. You are using the frequency on a shared basis, which means you must monitor the frequency before transmitting to ensure you are not interfering with another transmission. And should there be interference between two stations, responsibility for resolving the interference will fall on those two stations, the FCC will be very much hands off in the process unless there are some egregious or extenuating circumstances preventing resolution otherwise.
The devil is always in the details. If you can provide the call sign of the license in question, we can review the specifics in the FCC ULS database and figure out what’s what.
A good example of an exclusive use frequency will be NOAA weather radio (although the stations are not actually licensed by the FCC, since Federal agencies do not fall under the jurisdiction of the FCC, but rather NIST) – Nobody is going to be allowed to transmit on those frequencies except NOAA.
Note that the FCC does have very clear and specific exemptions for emergency communications-- the jist is that any true emergency communication will not run afoul of Commission rules, but that is a very limited and specific exemption.
If the MNS service is licensed on a non-exclusive basis, and is being used to communicate information during a genuine emergency, and there is a genuine need to continuously transmit to disseminate information related to the emergency, then the FCC will almost certainly let it slide.
Not NIST but National Telecommunications and Information Administration both are in the Commerce Department.
My bad, you are correct.
i would think that for emergency communications services there would be tight standards and regulations. if it was a shared channel you wouldn’t want a machine continuously transmitting a ‘school opening is delayed today’ message to block the channel to be used for other alert transmissions.
i understand and agree with the point of sending a SOS or Mayday or similar by an unlicensed operator by any radio method would not result in a fine or other sanction by the FCC.