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FM Broadcast Antenna

M

MarioMania

I just bought a BNC FM Antenna for my Micro FM Transmitter around the house

Most on ebay had like for the Air Band 118-136

Whats the different? all work the same, I hooked it up & I got a signal

Even a TV Antenna
 
A TV antenna that has VHF should also be an FM antenna, since the FM band sits between Channel 6 and Channel 7.

If you buy an aircraft band antenna, it should work for FM, with reduced efficiency. These things tend to be optimized in gentle curves, not steep cliffs
 
PTBoardOp94 said:
A TV antenna that has VHF should also be an FM antenna, since the FM band sits between Channel 6 and Channel 7.

If you buy an aircraft band antenna, it should work for FM, with reduced efficiency. These things tend to be optimized in gentle curves, not steep cliffs
Click to expand...
Way to encourage them to do something illegal.
 
Thanks for the replys

Also I have a hard time wording stuff, so just bear with me guys

Is there a site about to measure antenna hight, like I got like 27.5 inches on 106.1

that's the only clear frequency where I'm staying for now
 
MarioMania said:
Thanks for the replys
Also I have a hard time wording stuff, so just bear with me guys
Is there a site about to measure antenna hight, like I got like 27.5 inches on 106.1
that's the only clear frequency where I'm staying for now
Click to expand...
To build on what Kelly alluded to above, just be careful, @MarioMania as the FCC rules about Part 15 and "micro transmitters" are very clear, and come with restrictions. If you're connecting this type of antenna to your micro transmitter, you're most likely not operating your system legally.
 
MarioMania said:
Thanks for the replys

Also I have a hard time wording stuff, so just bear with me guys

Is there a site about to measure antenna hight, like I got like 27.5 inches on 106.1

that's the only clear frequency where I'm staying for now
Click to expand...
The formula for a dipole antenna in feet is 468 / f(MHz). Divide that in half for a quarter wave monopole.

A monopole antenna (1/4 wavelength) cut for 106.1 MHz will be about 26.5 inches long. It will also be illegal unless you cut your power output to about 11 nanowatts. That's 0.000000011 watts. You should be able to transmit only about 200 feet at the absolute maximum, probably much less, but if you're only broadcasting to yourself, that will cover your house and yard.
 
Yes I know about the FCC Part 15

The transmitter goes out like 200ft before it fades out

The houses I stay in, I don't own, just rent..So the Antenna is Indoors only
 
Do not modify the antenna. The FCC occasionally comes down on pirates. If by some chance the Commission drives by and determines you are going to faryou get a notice, the owner of the property will be named too. You will be evicted unless he wants to take on the FCC. The chances are small but as Clint Eastwood said "do you feel lucky".
 
secondchoice said:
Do not modify the antenna.
Click to expand...
Thank you for standing up to save Mario from himself. This is exactly why I frequently discourage posters from helping interested folks effectively 'play radio'. Time and again going a few feet within their home is no longer enough. Eventually, they want a more powerful transmitter or fool around with antenna gain.
 
MarioMania said:
My Micro transmitter is like like 1mW so it's not going to go far
Click to expand...
That's still too much with a 1/4 wave monopole. 1 mW ERP is about 90,000 times the legal limit for Part 15 FM. It could radiate further than you realize.
MarioMania said:
Anyways, the Antenna is indoors so
Click to expand...
So? If you live in a wood-frame house, there will be little to no loss between indoors and outdoors. Stucco is another story. The chicken-wire lath can attenuate signals by a factor of 20-40 dB in both directions.

This is what happens in my house. I use it to my advantange, keeping my Part 15 FM transmitter indoors and away from windows, while my ham antennas are outside, away from the house, and immune from all the digital hash indoors.
 
KeithE4 said:
That's still too much with a 1/4 wave monopole. 1 mW ERP is about 90,000 times the legal limit for Part 15 FM. It could radiate further than you realize.

So? If you live in a wood-frame house, there will be little to no loss between indoors and outdoors. Stucco is another story. The chicken-wire lath can attenuate signals by a factor of 20-40 dB in both directions.

This is what happens in my house. I use it to my advantange, keeping my Part 15 FM transmitter indoors and away from windows, while my ham antennas are outside, away from the house, and immune from all the digital hash indoors.
Click to expand...

no its not.. 1 milliwatt is 90,000 times the legal limit of part 15 fm?

No, its more like the legal limit is like 10mw or so? User RFry on here has explained this before.

1mw being 90,000 times the legal limit would be part 15 fm wouldnt get past the desk you put the transmitter on.
 
Either way, 11.43 nW into a unity gain antenna will get you 250uV/m at 3 meters.
 
SomeRadioGuy said:
no its not.. 1 milliwatt is 90,000 times the legal limit of part 15 fm?
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Divide it yourself. 1e-3 / 11e-9 = 90,909. 11 nW = -49 dBm.
SomeRadioGuy said:
No, its more like the legal limit is like 10mw or so? User RFry on here has explained this before.
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Way too high on FM, but OK for AM. 100 mW input on AM will get you 50-75 mW RF output. Combine that with a 3 meter antenna with a radiation resistance in the milliohms, and maybe a few microwatts will actually be radiated. Still good for 100-200 feet if installed properly.

The minuscule power is related to having an efficient antenna.
SomeRadioGuy said:
1mw being 90,000 times the legal limit would be part 15 fm wouldnt get past the desk you put the transmitter on.
Click to expand...
250 uV/m at 3 meters (11 nW ERP) is equivalent to about 25 uV/m at 30 meters.
 
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Realistically, it depends on where you are. A Part 15 with a more efficient antenna in Southwest Left Bumblef*ck, on an unoccupied channel, with unoccupied first and second adjacents, isn't likely to make a hill of beans to your 13 neighbors. OTOH, if you live on West 79th Street in Manhattan or in Westwood in L.A. or at the top of Potraro Hill in San Francisco, your garden-variety, conforming microtransmitter will probably hit 3,000 of your immediate neighbors, and you can't find a open channel for 100 miles anyway. (And that 100 miles is in the ocean, heading towards Bermuda.) So use your brain and some common sense.
 
^^^ Perhaps one might be able to get away with bending the rules in less populated areas, but the actual FCC policy that governs Part 15 doesn't change regardless of where one lives. The rules are the rules and it's a federal policy. There was a story just a few weeks ago about a guy operating a small independent music store in BFE, and he was running an unlicensed station playing "his" music and he mentioned it to a newspaper that included that tidbit in a news story about his business. Guess who came knocking? Guess who no longer has an illegal transmitter?
 
I have always wondered about the few surviving drive in theaters. The one I went to during COVID used a FM signal instead of speakers. I could pick it up about a half mile away when driving out.

Another question for folks with a lot of time on the hands: Could someone buy a couple of legal part 15 units and physically stack them at the proper height on the same frequency to get some "gain"? You didn't modify the unit.
 
secondchoice said:
I have always wondered about the few surviving drive in theaters. The one I went to during COVID used a FM signal instead of speakers. I could pick it up about a half mile away when driving out.

Another question for folks with a lot of time on the hands: Could someone buy a couple of legal part 15 units and physically stack them at the proper height on the same frequency to get some "gain"? You didn't modify the unit.
Click to expand...
That would mean you would likely exceed Part 15 field strength limits.
 
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