20 Watt FM Transmitter

[radiorobert]

I am wondering how much distance I will get out of a 20 watt transmitter with a standard antenna attached?

It will sit up about 20-40 feet off the ground.

The best I have been able to figure is about 10 miles TOPS on a car or large stereo system.

Otherwise good-strong coverage 2-3 miles?

Thanks

 

[Goat Rodeo Cowboy]

Your question is just bubbling over with issues and what-if's.

What is "a standard antenna"...? Are you talking about horizontal polarization only, or are you going with an antenna that splits the power into both vertical and horizontal.

Are you talking about a set up with conservative, industry-standard specs for a transmission line with minimum possible power loss in the line, or are you doing what some of the pirates and Part 15 people do and just run some kind of minimal cable.

If you are following the chatter about LPFM, you will find that 100 watts from an antenna 100 feet above ground may get you 5 miles.

I'm not sure how 20 watts and 20 to 40 feet above ground is going to get any 10 miles of coverage.

There is a website from Communications Research Centre Canada that can give you some starting ideas on coverage based on your local terrain. (Even though it is based in Canada, it has the data for topography of the United States.

Once you create maps with this site, you still have to deal with the question: how much signal does it take to drive a car receiver or large stereo system: 60 dBu? 50 dBu? 34dBu?

 

[TomT]

Find your elevation above sea level at Topozone or from a downloaded topo from USGS. 40 feet is about 12 meters. Assuming 20 watts into 50 feet of 1/2 inch foam cable into a circularly polarized single bay antenna your ERP will be about 9 watts.

Then use this to calculate your AHAAT for each direction:

http://transition.fcc.gov/mb/audio/bickel/haat_calculator.html

Then for each radial you can use this program to find your distance to a particular field strength contour:

http://transition.fcc.gov/mb/audio/bickel/curves.html

70 dbu is in-house listening, 60 dbu typical car radio, 50 dbu good fringe listening--on average.

Have fun.

 

[Radio-X]

with a 15w xmitter hooked up to one of those collapsable 5/8 antennas mounted 50' on a roof...got about 3-5 miles as the crow flies to static in hilly terrain. It would stop on 'seek' on a radio within sight of the building (about 1/2-3/4 mile)

So, given the slightly lower height and greater power, I'd think you will get 2-3 miles of listenable range. But it depends...

Radio-X

 

[radiorobert]

Thanks for the replies.

We were looking at standard horizontal polarization for antenna. I believe we are going to at least have to go to 100 watts or more. But we have immediate access to a 20 watt as a quicker start which is why I am asking. We would need to get almost the full 20 to make it count. anything below 15 won't cut it. Especially with the background RF and numerous metro signals in or near our area. My preference would be 250 watts at minimum. If I had my 'way' we'd be no less than 1000watts.

I am invovled with a non-profit looking to start up a station locally here in our community or possibly a larger neighboring community. I think we are going to have to go for something bigger than an LPFM or educational style license. We may have to uprgade to the big leagues which will take more money and time.

We have also considered pooling and going in as an investment as a full commercial operation.

Alot of open ends right now which may or may not ever materialize.

We are in the VERY early stages.

 

[Goat Rodeo Cowboy]

I am invovled with a non-profit looking to start up a station locally here in our community or possibly a larger neighboring community. I think we are going to have to go for something bigger than an LPFM or educational style license.

If you go for for NCE educational style license, you are not limited to low power. You may have trouble finding an open channel in your area. And just like the LPFM thing, you have to wait until the FCC gets around to having an application window.

I trust that you are looking around you to see if there is an existing NCE that is having hard times and might be open to acquisition or merger of interests. Sometimes church groups who have an NCE find it has become a financial burden. They might be willing to part with a station and take a multi-year promise of some time on Sunday mornings as payment or partial payment for the station.

 

[radiorobert]

I am invovled with a non-profit looking to start up a station locally here in our community or possibly a larger neighboring community. I think we are going to have to go for something bigger than an LPFM or educational style license.

If you go for for NCE educational style license, you are not limited to low power. You may have trouble finding an open channel in your area. And just like the LPFM thing, you have to wait until the FCC gets around to having an application window.

I trust that you are looking around you to see if there is an existing NCE that is having hard times and might be open to acquisition or merger of interests. Sometimes church groups who have an NCE find it has become a financial burden. They might be willing to part with a station and take a multi-year promise of some time on Sunday mornings as payment or partial payment for the station.

Yes, we are doing and going to be doing our due diligence as we move forward. There are some existing options in the area who we are thinking of approaching in regards to current operations. The appliacation period is what we are also preparing for to have our ducks in a row when it comes around.

 

[w9wi]

Are you in the U.S.?

 

[TomT]

Reality check:

1. After the last window for NCE apps, there is very little chance of getting a new NCE license unless you are in the middle of a desert.

2. So, as a practical matter, you will be looking at applying for an LPFM if and when the window opens.

3. The fCC has a channel finder:
http://www.fcc.gov/encyclopedia/low...gn=a99742107a-TRI_04-13-2012&utm_medium=email

Another source is Rec Networks: http://home.recnet.com/lpfm

4. LPFM transmitters must meet different standards than equipment used by other stations.
Believe only P-Tek, Bext and Nautel make equipment that is approved & will actually work.
Save your pennies--best unit is the Nautel VS-300, about $5K.

However, a good antenna is not expensive--look at SWR's CP antenna for around $600.

5. New regulations for towers over 20 feet will be a major expense. I have over $3K in various expenses on a 195 ft. tower--without turning a single shovelful of dirt. You may wish to secure a lease on an existing tower, or arrange to put a short mast on a tall building. Or build a bergfried.

 

[Nostalgia]

AAAAAARRRRGGGGH RadioRobert, are ye a pirate???

There is not (to my knowledge) a licensed FM service that would license a 20 watt transmitter (not counting translators since he is apparently wanting to originate programming, not relay it). There is the 10 watt LPFM (being phased out) and the 100 watt version subject to all the comments already made by others. Is the 20 watt transmitter that you have FCC type accepted for any particular service? I have visions of strange third-world transmitters from E-Bay floating around in my head! Of course, as w9wi has asked and remains unanswered- are ye in the good ole USA??

Wanna get into the radio biz and serve your community now? Read my post in the Community Radio forum "why does community radio have to be LPFM" and then look around your area for a small AM that the owner would (happily) part with for a reasonable price and you are good to go! Good Luck. aaaargh....

 

[radiorobert]

AAAAAARRRRGGGGH RadioRobert, are ye a pirate???

There is not (to my knowledge) a licensed FM service that would license a 20 watt transmitter (not counting translators since he is apparently wanting to originate programming, not relay it). There is the 10 watt LPFM (being phased out) and the 100 watt version subject to all the comments already made by others. Is the 20 watt transmitter that you have FCC type accepted for any particular service? I have visions of strange third-world transmitters from E-Bay floating around in my head! Of course, as w9wi has asked and remains unanswered- are ye in the good ole USA??

Wanna get into the radio biz and serve your community now? Read my post in the Community Radio forum "why does community radio have to be LPFM" and then look around your area for a small AM that the owner would (happily) part with for a reasonable price and you are good to go! Good Luck. aaaargh....

No not a pirate.

Just doing some research. I highly doubt the one I have seen is FCC accepted anyway. This would seem to be a ruled out option now the more research I do.

Yes, we are in the U.S.

The AM option has been discussed as well. The desire is to first rule out FM. Thanks for the info though. I will check out your post.

 

[andydallas]

when you start talking about a 'small' commercial station, you will be shocked at the amount of money you will spend, even if the station was given to you (it won't be)

Suddenly you are responsible for everything from public files to properly working emergency alert, to logging everything under the sun, then of course we have things like ASCAP/BMI/SESAC,,,you would be smart to get someone 'in your corner' in the industry that can help you look at this,,radio sounds like a lot of fun and a great way to help the community,,and it can be, but its also an industry closely regulated by the Federal Government,,,which means there are large checks to be written.

LPFM is a good alternative, you will find it is designed more for groups like yours and will take away a lot of the headaches

 

[BobOnTheJob]

LPFM is a good alternative, you will find it is designed more for groups like yours and will take away a lot of the headaches

and a lot of the revenue as well.

 

[Chuck]

LPFM is a good alternative, you will find it is designed more for groups like yours and will take away a lot of the headaches

and a lot of the revenue as well.

LPFM actually stands for "Low Power, Forget Money." Been there, done that.

 

[AnyHuman]

Transmitters are sold online for pretty cheap nowadays... I have one with 0.5 watts and a straight rod dipole antenna, gets me about 3 blocks in all directions with a great signal if no buildings in the way.

 

[Kelly A]

LPFM actually stands for "Low Power, Forget Money." Been there, done that.

Definitely this. There are an increasing number of more silent, or non-starting LPFM's than successful ones. Assuming you could, starting an LPFM now, would be similar to opening a new restaurant during the pandemic. In other words; bad idea.

 

[rfry]

A point that some may want to consider here is that legal, unlicensed use of the FM broadcast band in the US is limited to a transmit system producing no more than a 250 µV/m field at a distance of 3 meters in any direction from the transmit antenna (FCC 47 CFR §15.239). The normal, useful reception range of such a signal by a typical FM receiver is less than 300 feet.

For perspective, a 250 µV/m, free-space field is produced by a transmit power of about 11.4 nanowatts (0.000 000 011 400 watts) radiated by a 1/2-wave, center-fed dipole.

 

[kwthom]

🤷‍♂️

Nothing has substantially changed in a decade.