HFU HF Underground
Technical Topics => Part 15 AM and FM Station Operation => Topic started by: ThaDood on September 29, 2020, 1834 UTC
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Here's the full, unchopped, title: Radio Survivor - Social Distancing Sparks Interest in Part 15 Unlicensed Broadcasting, but Caveat Emptor. Here's the link, http://www.radiosurvivor.com/2020/09/21/social-distancing-sparks-interest-in-part-15-unlicensed-broadcasting-but-caveat-emptor/
On Part #15 FM, there no actual RF power out limit, but just that limiting FS limit of 250uV measured at 3 Meters away. I do remember that someone in the 1990's Panaxis EBN (Experimental Broadcaster's Newsletter) calculating with the possible RF OUT would be to a 1/4-Wave GND Plane Antenna, and it was something like 600pW - 800pW. That's picowatts, 10 to the -12! That small!!!
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I've been hearing about this, seeing the videos in my feeds with churches and others using part 15, and thought it's good that radio is being used as a cheap and simple way to serve an audience.
Well, if that's true, picowatts, a little power goes a long way.
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Well, there's still AM Carrier-Current Coupling, (Loading to the power lines.), that's still totally permissible, like some schools and colleges still do. However, lack of gear, with Radio Systems and LPB, Inc., gone bye-bye, and the idea of coupling to the power lines, seems to set most folks away from that idea. You can Neutral Inject, like my AM610 is. If a mega church parking lot is big enough, where they have a dozen light poles lighting that, you can couple to those power lines and easily cover that whole lot with less than a watt carrier. Not a new idea either, since many Drive-In Movie Theatres have done that for decades, after they trashed their pull-aside window speakers. (Remember them?) The smart owners just coupled into the old speaker wiring. Can still be done.
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Carrier-Current sounds like a good idea too. I can see at a school how they would use special wiring, to reach all of the buildings through wires branching out to them; more planning would be needed in that case.
For something simple, like at a church through the light poles, could the transmitter just broadcast through a an AC plug in the wall and transmit Carrier-Current that way? That would be even easier, with no antennas to set up!
I think churchgoers are more likely to accept AM for voice modulation to hear their pastor's voice.
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Splattering on aviation frequencies is not to be taken lightly. "I wanted to play Pixies and Concrete Blonde but some plane crashed..".
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Yeah... In AM Carrier-Current Broadcasting, coupling to the power lines is what I'm talking about. And, the electrical power lines are a leaky radiating antenna. You may have seen this at home, with those plug-in FM 'so-called' wireless intercoms. They operate in the 1750M Experimenter's Band, around 175kHz NBFM with a RF OUT of about 10mW. They are usually coupled with a capacitor and a can-like Low FREQ transformer network. AM Carrier-Current Coupling also requires a matching network that can handle some pretty low impedance values, like 10 Ohm, or lower. A Carrier-Current Coupler has an RCL network, that's usually adjustable, since every location with be a different impedance. I'm trying to find a site that has like a Radio Systems CP-15 Coupler, or the equivalent LPB one. Even a simple LPB T-8 would be a good one. Huh... I'll have to add the inside PIC's of the CP-15 that's on my AM610, the brown box seen in a PIC that's labeled Phase II. https://vk.com/realfreeradio?z=photo219315054_381150537%2Fphotos219315054 Yeah, my bench was a real mess years ago, but the station still rocks. UPDATES 10/1/2020: I've added more CP-15 PIC's to my VK page, just below the weekly programing listings, https://vk.com/realfreeradio
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I wonder why that Carrier-Current isn't promoted more, when it seems like the transmitters with antennas attached have websites with slick advertising and testimonials, but no one is doing that for Carrier.
Lots of people, like those in apartments and places where the can't put up outdoor antennas could use something like Carrier-Current, and you could take it anywhere and plug it in, seems like it would fill a need there.
Now on the coupler/tuners you've posted, it looks like there are a lot of step switches for the impedance and capacitance, but could this be done like a regular antenna tuner, like something from MFJ with capacitors and roller inductors, has someone tried?
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Coupling to the AC wiring seems to put people off, yet they do it with those intercoms from anywhere from 140kHz - 190kHz. So, it cab indeed be done. What some of us are experimenting with it the same coupling as those wireless intercoms, a medium wave transformer tied to two .1uF - 250V CAP's tied to the HOT and Neutral, have the HOT fused at 2A, and that simple of a coupler could do it. That's how the wireless LF intercoms are doing it, from what we've studied. So, that could be a nice Plug & Broadcast package to have to get on-air in your neighborhood. Oh!!! Where else do they use Carrier-Current Coupling? Mining. https://www.cdc.gov/niosh/mining/works/coversheet906.html