Here's an interesting question:

How do I build an portable FM transmitter?

This doesn't qualify as Amateur Radio in the US, on at least two counts:

  1. (with some assumption) it involves operation in commercial bands
  2. it involves broadcast

However, it is about amateur radio, in the sense of non-professionals doing stuff with radios for fun. I'd hazard a guess that many hams would find this an interesting question, as much of the problem of building an FM transmitter is independent of frequency of operation or intended use.

The intentions of the question are also questionably legal. I know that in the US, it's legal to transmit on the commercial FM band with very low power. I know this because FM transmitters designed to connect a music player to a car radio that does not have an audio input are sold. I'm guessing they operate under FCC part 15 rules. However, I believe such a device requires certification, and "broadcast" suggests the goal is to transmit with enough power that other people can hear it. I'm guessing that's contrary to part 15.

Are questions such as this on topic? Why, or why not?

  • $\begingroup$ My feeling is that it's off topic because it's about broadcasting, which is generally not permitted in amateur radio, but I'll have to look a bit more closely at it before being able to say anything much for certain. It's also very likely off topic anywhere on SE because it is so broad (the "if you can imagine a whole book" criteria). $\endgroup$
    – user
    Jan 28, 2014 at 14:09
  • 2
    $\begingroup$ @Phil Frost US, US, US, US.... I really don't want to sound disrespectful, but from where did you get the idea that OP in that question is from the USA? Why all the obsession with US and FCC? Also the fact that something is purchasable does not in general mean that it's legal to use. I do know of some people who assumed that just because you can buy a particular piece of equipment and everyone is using it, it's legal to use it. Some quite stiff fines taught them otherwise. $\endgroup$
    – AndrejaKo
    Jan 29, 2014 at 20:20
  • $\begingroup$ @Phil Frost In any case, I think it's good thinking to discuss where we'll draw the line between the two types of amateur radio you listed and I also think that it would be good idea to think what we'll do in edge cases. $\endgroup$
    – AndrejaKo
    Jan 29, 2014 at 20:21
  • $\begingroup$ @AndrejaKo because I'm not an expert in the world's radio regulatory agencies. Remind me to call out your obsession for Serbia when you answer a question on regulations there. $\endgroup$ Jan 29, 2014 at 20:22
  • 2
    $\begingroup$ @Phil Frost Don't worry, I will! :) $\endgroup$
    – AndrejaKo
    Jan 29, 2014 at 20:22
  • $\begingroup$ In any case, I seriously doubt operation in the commercial FM bands is legal under an amateur radio license in any jurisdiction. Is it legal in Serbia? $\endgroup$ Jan 29, 2014 at 20:23
  • $\begingroup$ @Phil Frost It may not be under Amateur Radio, but in some areas it may be under what you defined as amateur radio. For example, here in Serbia (don't forget to call me out on my obsession with Serbia!), under something called "Rulebook on the use of radio frequencies by the general authorization regime", you can broadcast in the 87.5-108 MHz range as long as your E.R.P. is under 50 nW. $\endgroup$
    – AndrejaKo
    Jan 29, 2014 at 20:29
  • $\begingroup$ @Phil Frost One other thing I wanted to mention in an answer I'm writing is that there were cases where hams were allowed to do broadcasting in the commercial TV bands for a while after analog TV shutdown. Also in some cases, amateur radio operators got permits for specific experiments not involving traditional HAM technologies. I think that we should be in general open to such questions. Of course, I completely agree that people should get to know their own regulations and should comply with them. $\endgroup$
    – AndrejaKo
    Jan 29, 2014 at 20:32
  • $\begingroup$ @Phil Frost Then there's also the point of borderline questions where technology used by hams is used by other radio services as well. I think that we should be open to such questions, but focus on the Amateur Radio angle in answers. I primarily answered the particular question asked here because the method I provided doesn't depend much too on actual frequency used, for very short range at least. $\endgroup$
    – AndrejaKo
    Jan 29, 2014 at 20:37
  • $\begingroup$ @AndrejaKo you should put these comments in an answer so people can vote on it. $\endgroup$ Jan 29, 2014 at 20:38
  • $\begingroup$ @Phil Frost That's what I'm planning to do. $\endgroup$
    – AndrejaKo
    Jan 29, 2014 at 20:42
  • $\begingroup$ Well I wrote an answer (after some 6 hours of writing), but I can't post it due to CAPTCHA errors. :( $\endgroup$
    – AndrejaKo
    Jan 30, 2014 at 12:59
  • $\begingroup$ @AndrejaKo SE usually saves your draft automatically. If you go do some stuff on the site then come back it should be there, but I'd copy&paste it to a local text editor to be safe. $\endgroup$ Jan 30, 2014 at 13:01
  • $\begingroup$ Looks like I was able to post from Internet Explorer. $\endgroup$
    – AndrejaKo
    Jan 30, 2014 at 13:29

1 Answer 1


What's asked in this meta question is a bit complex, so the answer is going to be a bit complicated...

I see several angles here:

Technologies commonly used for Amateur Radio and technologies used for other types of radio transmissions, which may or may not be used by amateurs.

Experimentation by amateur radio operators but not by Amateur Radio operators.

Legal side - what may or may not be legal in certain area, whose responsibility it should be to judge legality, should we provide information that could lead to acts that could be perhaps illegal.

Probably a few more I can't think of right now.

I'll try to briefly discuss all of them and offer my opinion.

In case of technology angle, in general I don't think that we should be very strict. Many non-Amateur Radio technologies are making their way into Amateur Radio and many Amateur Radio are closely related with other general radio technologies. We now have OFDM over voice used for Amateur Radio, even though OFDM isn't a very traditional Amateur Radio technology. I've heard of cases where for example Amateur Radio operators got permissions to operate in bands abandoned by analog television for a while or to use spread spectrum techniques. Furthermore, it seems that in some areas there are exceptions even for most common rules. On this site, I've heard that Amateur Radio operators in certain jurisdictions may use encryption for configuration of amateur radio satellites. Furthermore even "broadcasts" by Amateur Radio operators may be allowed in some cases. I've seen amateur radio weather balloon projects where the radio on-board the balloon's payload is basically making an unidirectional transmission of telemetry. I've also heard on this site that US Amateur Radio operators are allowed to retransmit some NASA broadcasts for example.

So my point basically is that even technologies not commonly used by Amateur Radio operators can be of interest to them and may have aspects directly related to what's commonly used by Amateur Radio operators.

Next, there's the experimentation by radio amateurs part. I don't see why this would be particularly off-topic, since many things would hold true for both Amateur Radio and amateur radio experimentation. Furthermore, amateur radio experimentation may impose some restrictions that Amateur Radio operators may not face. I think that working around them may be fun for the community, but in the end, that's for community to decide.

Finally, there's the legal side. I'm not really certain what to say here, except that I don't think that we should expect users to first prove themselves to us in some manner before actually answering the question. On the other hand, I do think that it is OK to ask in a non-aggressive, non-accusatory way about something that looks potentially illegal in some part of the world and to offer guidance in a friendly manner. I could be overgeneralizing, but I've seen lots of flame-wars on the Internet forums related to radio regulations and I think that in cases of dubious legality, we should always keep cool head and be open to counterarguments.

It is important for us to keep in mind that we can't actually prevent someone from breaking the law and that a hostile response will often just send people away to another source of information. On the other hand, a friendly approach can sometimes help people realize that they're wrong (if they're wrong).

In my opinion, legality problems closely related to Amateur Radio should be definitely on-topic. I don't think that any direct questions related to legality from other radio services should be on-topic, but I do think that legality may be addressed in the manner stated above.

One more thing that should be kept in mind are the "gray" areas where regulative isn't clear or doesn't exist. In such cases, I think that we should encourage users to try to seek out information themselves and to try to find out who can give then an authoritative source of information.


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