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12v High Power FM Transmitter

CallumA

Jul 22, 2013
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Hi!
I've been having a look at this: http://www.electroschematics.com/19/300w-fm-88-108-mhz-amplifier-tp9383/

It's a 300W FM amplifier running @ 28V. I have 2 questions about it:

1. Will it run on 12V? I don't need too much power so if it would run what kind of power output could I expect?
2. What kind of input power does it want? Is 15W OK? (http://www.eee-lab.com/radio/fm-radio-transmitter/47-hr-fm-t)

If that's not possible, do you have any ideas? I've been searching for half the day for a transmitter and a chain of amplifiers that can output >50W with a 12V (or 24V if there's nothing on 12V) input. The higher output power that's possible the better as long as I can adjust it.

Thanks!
 

davenn

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Sep 5, 2009
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Hi callum

for a 300W transmitter you will need a commercial transmitting licence ( anything over a few 10's of Watts and you will)
the station setup would have to be properly inspected by the authorities to make sure it conforms to commercial broadcasting standards before they would issue a licence
you would have to apply for a frequency. They would then allocate a frequency that isn't going to interfere with other FM band transmissions or reception

hope you have a good bank balance of quite a few $1000 to get set up

even at 15W of that low power transmitter, you would still need a transmitting licence
as its well above the 0.5 - 1W level for experimental work

from a technical POV of that big amp ..... the transistors may be specified for 28V and they may not have stable operation at a lower voltage ... data sheets for the transistors would confirm that.

cheers
Dave
 

CallumA

Jul 22, 2013
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Hi callum

for a 300W transmitter you will need a commercial transmitting licence ( anything over a few 10's of Watts and you will)
the station setup would have to be properly inspected by the authorities to make sure it conforms to commercial broadcasting standards before they would issue a licence
you would have to apply for a frequency. They would then allocate a frequency that isn't going to interfere with other FM band transmissions or reception

hope you have a good bank balance of quite a few $1000 to get set up

even at 15W of that low power transmitter, you would still need a transmitting licence
as its well above the 0.5 - 1W level for experimental work

from a technical POV of that big amp ..... the transistors may be specified for 28V and they may not have stable operation at a lower voltage ... data sheets for the transistors would confirm that.

cheers
Dave

Thanks Dave.

My plan was to not have it running at 300W at max but rather have it variable over some (much lower) range. The 300W schematic only relates to the question of whether I could get it running at a reasonable power on lower voltage.

My issue is I have a large premises with some thick-walled buildings with a lot of internal walls as well as warehouses which I would like to have the FM signal penetrate. I've found it difficult to get very far with a reasonable antenna on a 15W transmitter. I'd also be running far from any FM stations in the area (we get very few here anyway - nothing above 101.1 for example so 108 could be an option). These buildings are also quite far from the nearest built up area.

In the UK we have a regulator Ofcom which investigates only by complaint and as the transmitter would not be reaching far out of the walls and isn't on top of anything else this shouldn't be a problem.

While, strictly speaking, this would not be allowed (I think) no issues should come of its use. What usually happens anyway is they ask the operator to shut down the station before taking any action.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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We already know that the 15W you're transmitting is well above the legal limit in the UK or just about anywhere else for that matter. Aiding you to further exceed power limits would put Electronics Point in legal deep water.

Chris
 

CallumA

Jul 22, 2013
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We already know that the 15W you're transmitting is well above the legal limit in the UK or just about anywhere else for that matter. Aiding you to further exceed power limits would put Electronics Point in legal deep water.

Chris

I'm starting to think just wiring up a load of readily available transmitters from China (through a distributor in the UK for speed) around the place might be the way to go anyway. They're quite cheap in bulk and are probably legal too. As a bonus it could possibly work out cheaper in wiring and then subsequent electricity bills.

I don't need the FM at all this week so it's probably the best time to get it all done.

Definitely don't want to get Electronics Point or anyone on here in any trouble with the mods/admins or anything so maybe the thread should be closed for further comment?

Callum.
 

CallumA

Jul 22, 2013
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Bwahahahahahha.

Sorry.

More legal then. Either way, there's a very low chance it'd be detected as above legal limits outside of buildings anyway if it can even be picked up with a reasonable radio.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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What are you using it for,.. music?

Chris
 

CallumA

Jul 22, 2013
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No, just either silence and then a voice broadcast every now and again - a bit like a more budget kind of announcement system you get in shops with less internal wiring everywhere
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
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When you say "silence" do you mean that you're transmitting a carrier? Or would you only transmit when you have audio.

The carrier on its own (especially at the power levels you're suggesting) would be potentially as disruptive as a modulated signal.

Do you have a network connecting these buildings? You could probably piggyback some VOIP application (or maybe shoutcast) over it.
 

CallumA

Jul 22, 2013
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When you say "silence" do you mean that you're transmitting a carrier? Or would you only transmit when you have audio.

The carrier on its own (especially at the power levels you're suggesting) would be potentially as disruptive as a modulated signal.

Do you have a network connecting these buildings? You could probably piggyback some VOIP application (or maybe shoutcast) over it.

I am broadcasting the carrier so that there is no static after and it just simplifies things.

I think in the end it would just be easier to use a bunch of smaller transmitters of a much lower power inside buildings so that wouldn't be disruptive.

There is a network between buildings however I'm not sure it would be cost effective to have a computer of sorts broadcasting the FM - although the Raspberry Pi can transmit FM and as it's CE marked strictly speaking it's legal here so that could be a good possibility.
 

CDRIVE

Hauling 10' pipe on a Trek Shift3
May 8, 2012
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I am broadcasting the carrier so that there is no static after and it just simplifies things.

Simplifies things! :eek:

It sounds like you're using this like a wireless PA system. Is that what this is?

Large commercial buildings usually have an extensive telephone system with gobs of unused pairs. Have you explored this? I did this in a very large hospital.

Chris
 
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