Suggested Sticky: Guide to Unlicensed Operations

Discussion in 'Wireless & RF Design' started by WBahn, Nov 16, 2013.

  1. WBahn

    Thread Starter Moderator

    Mar 31, 2012
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    Not surprisingly, threads dealing with unlicensed operations are a common occurance here. They range across the spectrum from people wanting to transmit for miles to people wanting to transmit from one side of a lab bench to the other. What many/most of these posters lack, in addition to what they are asking specifically about, is any awareness/knowledge of whether what they are doing is even legal.

    It would seem like a really useful sticky would be something that peeled back the onion at least a bit and talked about the general guidelines for the kind of operations that are permissible for an unlicensed transmitter. Yes, these are going to vary from country to country, but there are probably some pretty common qualitative things they have in common.

    In particular, I'm thinking of something that would give people a pretty good idea of how they can operate and either make measurements confirming that they are in compliance or limit their design in such a way that it ensures compliance even without making measurements.

    As an example, one of the things I would like to do in the next few years is develop some hands-on electronics labs in which students build simple transistor-based transmitters and receivers using different modulation schemes. From a practical standpoint, it would be nice if this can be done in a completely unlicensed way and since the range need only be sufficient to get from one side of a room to the other I think that should be possible. But I will want to design the labs so that I have confidence that the students will be in compliance.

    I did some searching a few years ago and found some stuff, including some on the FCC website, but I didn't find much that would have been useful for a simple experimenter to use in order to ensure compliance.

    Any of you hams interested in throwing something together -- even if it's mostly links to sites where this information resides?
     
  2. bertus

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    Apr 5, 2008
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  3. WBahn

    Thread Starter Moderator

    Mar 31, 2012
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    The lowest ISM bands are a possibility but even the lowest, 6.8MHz, is higher than I would like the projects to start out at given that I would like something that can be readily done on solderless breadboard or wirewrap. Later projects can move into techniques that are conducive to higher frequencies, but would still need to be doable with scratch-built techniques.

    I looked through you RF related links thread before I posted this and didn't spot anything that looked like it would address unlicensed operations.

    I'm hoping to start with work in the AM broadcast band because that is low enough in frequency that lumped component models should suffice, parasitics on breadboards should be largely ignorable, and external transmitters and receivers are readily accessible so that students can start with a receiver and listen to local AM stations and then move to AM transmitters and use a cheap radio as their receiver. My understanding is that Part 15 allows this and even allows educational institutions to use higher power than John Public provided field strength limits are adhered to at the edge of campus. Similarly, operation on the FM broadcast band would be a nice match for later projects.

    The big thing in either case is being able to verify that the transmitters are within the legal limits and that involves using suitable field strength meters. What would be truly wonderful would be if I could find a design for a home-built field strength meter that could be one of the projects that students construct.
     
  4. bertus

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  5. Art

    Distinguished Member

    Sep 10, 2007
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    Kids these days modding walkie talkies to have private channels!

    I want to know how medium wave AM is modulated and broadcast,
    and also how to make a bunch of tuned circuits for different shortwave bands.
    In my radios, the MW and SW tuning circuits are just alternately shorted when
    the other is selected, so it should be possible to make a bunch more.
     
  6. Art

    Distinguished Member

    Sep 10, 2007
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    When those old radios that don't have proper tuning gangs
    are tuned by sliding a coil across metal, is that because it changes inductance?
    and does there need to be a fixed capacitor in that circuit?
     
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