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 Post subject: Super Simple FM transmitter
PostPosted: Mar Fri 02, 2018 3:00 pm 
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Joined: Mar Thu 01, 2018 1:30 am
Posts: 135
Range is 50 meters.

It transmits on third harmonic of the crystal frequency or 90 MHz.
A band pass filter can be used to filter the output and fed to a two stage transistor amplifier for
500 mW output. Fidelity is quite good and music sounded okay.

Schematic https://imgur.com/a/xuSgV


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 Post subject: Re: Super Simple FM transmitter
PostPosted: Mar Fri 02, 2018 3:56 pm 
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Joined: Feb Sun 02, 2014 9:13 pm
Posts: 1864
Location: Roanoke, VA
Dare4444 wrote:
Range is 50 meters. ...
A band pass filter can be used to filter the output and fed to a two stage transistor amplifier for 500 mW output....

Either of those make it illegal in the US.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: Super Simple FM transmitter
PostPosted: Mar Fri 02, 2018 4:08 pm 
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Joined: Mar Thu 01, 2018 1:30 am
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Yes I am aware. But the output of BPF can be directly connected to an antenna.
Range would be less than 50 meters with a 1/4 wavelength antenna.


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 Post subject: Re: Super Simple FM transmitter
PostPosted: Mar Fri 02, 2018 7:50 pm 
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I love the simplicity of it. From the time I was in the fifth grade, I've played with simple transmitters. FM was always intimidating to me, so the simpler, the better.

Dare4444, since you are new here, welcome to the forum. I appreciate your contributions.


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 Post subject: Re: Super Simple FM transmitter
PostPosted: Mar Fri 02, 2018 9:26 pm 
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Dare4444 wrote:
Range would be less than 50 meters with a 1/4 wavelength antenna.

That may or may not be legal. The only way to make sure that it is legal would be to conduct a field intensity survey using a calibrated FM field intensity meter such as a Potomac FIM-71. Doing so requires some experience (I have done such surveys for commercial FM stations).

Commercial Part 15 FM transmitters are restricted to using the manufacturer's supplied antenna. For anyone operating a Part 15 FM using anything other than a commercially built transmitter and antenna the burden of proof of proper operation is on the operator.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: Super Simple FM transmitter
PostPosted: Mar Sat 03, 2018 2:33 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 3938
Location: Cortez, Colorado
Give it 10 years, there may be no AM or FM. If Iheart can't make money from radio, and they go bust, I doubt anyone will buy the stations, and they'll go off the air or have to be subsidized.


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 Post subject: Re: Super Simple FM transmitter
PostPosted: Mar Sat 03, 2018 3:23 pm 
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Location: Roanoke, VA
iHeart can't make money from radio because they have constantly cut local personnel to try to increase profits. They have been getting their butts handed to them in markets like mine where locally owned stations that are less profit-hungry, locally staffed, and locally programmed are delivering a local product. Radio listeners are not stupid - they can tell the difference between a station that serves the local audience and has jocks that they can see around town, and one that is a clone-programmed jukebox staffed by jocks from who knows where.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html


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 Post subject: Re: Super Simple FM transmitter
PostPosted: Mar Sat 03, 2018 11:54 pm 
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Location: SoCal, 91387
Dale H. Cook wrote:
For anyone operating a Part 15 FM using anything other than a commercially built transmitter and antenna the burden of proof of proper operation is on the operator.

Given that, as long as the transmission range is constrained to be within their specification, the xmtr would be legal. Practically speaking however, as long as no one complains, it's good. if I transmit 150 feet out, but the nearest neighbor is 300 feet away, I'm breaking strict guidelines but harming no one.

_________________
\\\\\\\\\\\\\\\\\\\\\\\\He Who Dies With The Most Radios Wins//////////////////


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 Post subject: Re: Super Simple FM transmitter
PostPosted: Mar Sun 04, 2018 1:04 am 
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fifties wrote:
Given that, as long as the transmission range is constrained to be within their specification, the xmtr would be legal.

That specification is a given field intensity at a given distance, and the only way to know that is to measure it with a calibrated field intensity meter.

Enforcement Bureau is on the warpath for pirates. I would advise those operating Part 15 FM to be wary and to be certain that they are in compliance.

Dale H. Cook, Radio Contract Engineer, Roanoke/Lynchburg, VA
http://plymouthcolony.net/starcityeng/index.html


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