Hi, Sean. I hope you get a great success in your station. I also establish my own FM radio station recently. My good friend suggest me buy a low power FM transmitter on website: . The seller is a kindly man to provide me with much information about the transmitter. The wireless art is so attractive. I sincerely want to communicated with you about the radio station.
Have a great day.
Louis
Louis, I viewed the website you linked and it appears that these transmitters will require a license to use. Perhaps I missed one which would be OK but remember that in the US the Part 15 rules limit radiated field strength so that about 200 feet of range is expected on FM with unlicensed used of a transmitter.
Neil
Neil, thanks for your tips. The saller said their low power transmitter met the FCC requirement. The moder is CZE-05B. The follow link is its specific information: http://www.fmuser.net/content/?615.html. Please kindly give me some suggestions about it. I bought a low power to experience the attractive wireless technology.
Louis
Louis,
The transmitter in the link could be used in the US under part15 rules but the proper operation depends on the user. FM is difficult because the limit is on the field strength and not on the transmitter power. The 50 mW listed in the specifications will greatly exceed the legal limit if connected to an efficient antenna.
I do not believe that this unit meets FCC certification requirements since it features a standard BNC antenna connector. FCC rules require either an integral antenna or a unique connector which can only be matched to their antenna with which certification was obtained. If certification is important to you then ask them for the FCC identification number. Chances are they do not have one.
That being said, such a transmitter can be legally used if the field strength is limited per the rules. This is usually done by using a short antenna adjusted to give about a 200 foot range on a portable receiver. This is not a very good method of assuring legal operation but it is probably close enough. FM users do this with the kit transmitters which are not certified and there are no problems. Others ignore the limits and receive citations.
My preference is to use AM for part 15 broadcasting since under Part 15.219 the limits are easy for the user to assess, such as 100 mW power input and antenna + transmission line + ground lead length total limited to 3 meters. This typically gives more range than on FM.
The transmitter looks as if it will work for unlicensed broadcasting but you will need to be careful when setting the antenna for the range.
Neil
Hi, Neil. Thanks a lot for your sharing. You mentioned that let it legal depended on the antenna that I connected. So he recommended me to buy this kit: http://www.fmuser.net/content/?616.html. It included a BNC short antenna. Maybe I should make a test of it before I used it. The 200 foot is about 61 meters. I think it can't cover so far with this antenna.
As your suggestion, I consider why the AM transmitter will be hotter for wireless enthusiast in U.S. But I knew few about AM equipment. Are AM very different to FM? I pay more attention on the stereo. Are there lot differences of the audio performance between them?
Glad to communicate with you.
Louis
Yes. FM is easier to set up and use. Just turn on, extend antenna, and set frequency and away you go. Fm has much better sound fidelity and no noise interference. Also signal is not blocked by concrete and steel like AM is.
AM is not near as good as FM and is plagued by all the electrical noise that would make it almost impossible to listen in your home with a weaker signal. Also an AM transmitter is much more involved to set up. To get the distance people get here on the forum you have to have a house with your own property or large backyard to have an outdoor antenna and you have to dig up half the yard to install the buried radial wires. The antenna and loading coil is more complicated too.
Mark
AM is not near as good as FM and is plagued by all the electrical noise that would make it almost impossible to listen in your home with a weaker signal. Also an AM transmitter is much more involved to set up. To get the distance people get here on the forum you have to have a house with your own property or large backyard to have an outdoor antenna and you have to dig up half the yard to install the buried radial wires. The antenna and loading coil is more complicated too..
Well, that is true.. to an extent.. but broadcasting AM is not nearly as bad as you make it sound. First off, if listening just in your home in the general vicinity of your transmitter the sound quality is going to be excellent, and electrical noise will actually be pratically non existent as long as your within say a block radius of your transmitter.. then as you get farther away then electrical noise can become gradually more evident..
As for an AM transmitter being more involved to set up.. Again, that's only partially true.. It can be as simple as applying power, using a basic wire antenna, no ground, set the transmitter on your desk, insert audio and begin transmitting.. With such an install you will most likely exceed the legal range of a part 15 FM transmitter.
Setting up an AM transmitter only becomes an more involved proccess when you decide you wish to improve the performance with a more elaborate install involving a more advanced grounding system and/or antenna system.
If you want to be able to broadcast legally farther than 200 feet (in the US), then choosing AM over FM is a no-brainer.
Ah.. I should mention that I base those observations on the performance I experience with the SSTran 3000 and the Rangemaster AM transmitters.. I have no familarity with how any other AM transmitters might perform..
That's what I was just about to say.
Me too.
Hi Everyone
I am back was out ill for a little but but now I can get back up here and
talk. Anyways Neil is very correct. FM is really going to be based on
that 250uv at 3 meters away from the antenna.
This is a Chart that can give you an ideal on how far FM will reach
depending on the sensitivity of the radio.
Ok if you are in this chart you will meet FCC requirements.
Realize the best FM receiver I have ever found only had a 1.7uv senstivity.
This is the best receiver,so when you look at this chart then you will know
your real distance I also sugest if you are going for these distances you better
have a good field strength meter that measure in microvolts ,so you can show the
FCC you took readings. This test equipment is quite expensive to take these reading.
Ok for the FM part 15 FM distance chart.
This is the distance from the antenna. **
Meters** Feet** Field Strength reception Area total coverage in all directions
3 10 250uv 314 FT
6 20 125uv 1256 FT
12 39 63uv 4800 FT
24 78 31uv 19113 FT
48 157 15uv 1.8 Acres
96 315 7.5uv 7.2 Acres
192 630 3.8uv 28.6 Acres Special note on this
384 1260FT 1.9uv 114 acres Close to 1/4 mile away.
Realize this really is the limit because I have never found a receiver below
1.7 microvolts sensitivity on FM radio.
768 2520 .95uv 458 acres
1536 5036 .5uv 1830 acres this would be very close
to 1 mile from your antenna and I have never come across an receiver with a
.5 uv sensitivity. This would only be possible with a receiver with
a good yagi or beam type antenna on the receiver out doors on a roof of a home.
Your neighbors would really have to go to alot of effort to hear your station 1 mile
away but it possible with a very good receiver set up.
The average boom box receiver or Car radio is not going to hear you a mile away.
if you look on the chart the 48 to 96 meters is where you are goinng to fall
in with a car receiver.
If the car has a really great antenna and a very expensive receiver you could
possibly get where the chart read 192 meters and 630 ft.
Wow 630 FT not really all that good of coverage at best. Wow AM stations
have a lot better coverage.
Anyways this is reality and FM under part 15 really takes an effort to set up
for the most range legally and also your listeners have to really set up
a good antenna up at their homes to get you.
If you ever seen those really large TV antennas radio shack sold in the old day claiming they could receive TV for about 190 miles. One of this antenna had
about a 125 mile range on FM radio. if your listeners use one of those on
a nice receiver mounted on the roof . Well they may actually get you clear
at 1 mile away or a 1 1/2 miles. This would make up for the receiver sensitivity.
You would still be in accordance with the FCC but the listeners would just
have a set up that goes beond what the FCC thought of.
There you have it. There is some FM transmitters that are FCC certified to
transmit 250uv @ 3 meters and the antenna is already mounted on the transmitters.
These run from about $250 to around $450.00 . I have priced them.
output power on these transmitters is about 1 milliwatt going into a antenna
at an exact length so the transmitter will not emit more than the 250uv @ 3 meters.
50 mw will get you fined big time because you would have to have an antenna of
almost no length at all.
Almost all FCC approve FM part 15 transmitters do not exceed 1 mw output.
This is how small the signal really is.
I hope this helps out some.
special note this is a really good receiver on FM radio.
Sangean ATS-803A This receiver has a 4 microvolt sensitivity on FM Radio.
So it should be possible to here your signal close to 630 FT away on this radio.
The range of your FM signal really relies on how good of a receiver the person
uses. Also if the person uses a good outdoor FM antenna on a nice stereo receiver
this improves your chances of being heard.
Here is a bit more detail on the subject of Part 15 FM systems.
A rated input sensitivity of 1.7 µV for an FM receiver is the r-f voltage needed across its antenna input terminal impedance to produce a certain signal-to-noise ratio in its audio output waveform. So that sensitivity rating is not the field intensity in µV/m that is needed at its receive antenna.
For example at 107.9 MHz, a typical "whip" receive antenna about 30" long needs an arriving field intensity of about 5 µV/m to produce 1.7 µV across the typical 75 ohm impedance at the antenna input terminals of the receiver.
Below is a graphic showing the free space fields for an FCC-legal Part 15 FM system (the red line in the graph) and several others. The power needed to radiate the maximum legal field is extremely small: 11.43 nanowatts (0.000 000 011 43... watts). Systems operating with transmitter powers of even 1/10 mW (and above) can produce fields far above the FCC limit for Part 15 FM unless their antennas radiate almost none of that power.
Reflections of these signals from the earth and from buildings in the area of the transmit and receive antennas can produce net fields at some locations that can be as much as twice as great as for a free space path. But in other locations they might be only ~1/10 as great as the free space path. This effect often is easy to notice when listening to a weak FM broadcast station on a car radio, where the audio has short intervals of high noise/distortion as the car changes its location by as little as five feet (sometimes called "picket fencing").
There are two considerations for this, for Part 15 FM systems:
1. If the field intensity that the FCC measures is in a location where the fields are higher than the legal free-space value, they might conclude that the transmit system was non-compliant even though it was not.
2. If an unlicensed operator judges the amount of power being radiated by the performance of an FM receiver at a location where the fields are lower than the legal free space value, it might lead to excess radiated power -- and draw attention to that operator.
Hi Rich
You are very correct on everything you say. I was just showing what
I went by. I had a very expensive Field strength meter at one time that you
programed in that you were testing. Say you were on 100Mhz then you had the field
strength meter tuned to 100mhz. It also had the antenna set up at the correct length
so you would get the most accurate reading of what your transmitting antenna
was radiating. I sold this meter off,but I found it not worth spending thousands
of dollars just to find out I had 250uv @ 3 meters from the antenna.
Yes you are correct on the power ratings of the transmitter. I found FCC
certified FM transmitter that would only radiate 250uv and the antenna was built
coming out of the transmitter. The antenna was very small ,but the transmitter
was rated at 1 mw,so the antenna had to be very small to make sure that it would
not over radiate. That transmitter sold for around $500.00,and I still have the
name of that transmitter somewhere. It came in stereo or just plain FM.
They really sugested using just plain FM bacause the Stereo signal would drop out
fast at any distance from this transmitter. Also I found myself having to place
this transmitter into a weather proof box because the antenna was just a telescopic
type you find on small FM receivers. Really not an impresive antenna,but it
would not allow more than 250uv to be radiated. I ran power and audio cabels
to the transmitter in this weather proof box that kept the transmitter dry.
I ounted it up high on a mast and had pretty good results,but I really found
going with AM signal was much better. Also you are not limited by the
field strength on the AM bands. You are only limited by the performance of the
transmitter and the quality of antenna you use.
Yes it alot more work to lay ground radials and build a higher effient antenna but
I have found AM signal with part 15 far exceed that of the FM under part 15.
Part 15 FM is really good if you live in a city area in the country like I am
it cannot serve as a good station beacause you will not reach a listing audiance.
I will stick with AM part 15 because it works better for me.
My sugestion if you are going to do FM part 15. buy the best field strength meter
you can get. Take reading at 3 meters from your antenna on all sides of your antenna.
That means north,south ,east,and west. Make sure when you are 10 ft from your
antenna that you do not get a reading above 250uv. 10 feet not that far from your
antenna and you can get good readings. Make a log record the time ,date of when
you did this and keep a weekly log of this. Make sure you label what test equipment
you used to measure the field striength. The Good meters are FCC certified and also
make sure you have a calibration date on your meter.
Believe me if your power log is up to date and you can show the FCC you were trying
to keep good receords of your station radiated power this will be taken in
consideration when something comes up in question.
I know because I did this for large radio stations also.
Please know that field strength meter will not be cheap ,so realize what you are
getting into if you really want to keep in accordance with part 15.
Richard chart is very good.
Thanks
Hi Rich
You are very correct on everything you say. I was just showing what
I went by. I had a very expensive Field strength meter at one time that you
programed in that you were testing. Say you were on 100Mhz then you had the field
strength meter tuned to 100mhz. It also had the antenna set up at the correct length
so you would get the most accurate reading of what your transmitting antenna
was radiating. I sold this meter off,but I found it not worth spending thousands
of dollars just to find out I had 250uv @ 3 meters from the antenna.
Yes you are correct on the power ratings of the transmitter. I found FCC
certified FM transmitter that would only radiate 250uv and the antenna was built
coming out of the transmitter. The antenna was very small ,but the transmitter
was rated at 1 mw,so the antenna had to be very small to make sure that it would
not over radiate. That transmitter sold for around $500.00,and I still have the
name of that transmitter somewhere. It came in stereo or just plain FM.
They really sugested using just plain FM bacause the Stereo signal would drop out
fast at any distance from this transmitter. Also I found myself having to place
this transmitter into a weather proof box because the antenna was just a telescopic
type you find on small FM receivers. Really not an impresive antenna,but it
would not allow more than 250uv to be radiated. I ran power and audio cabels
to the transmitter in this weather proof box that kept the transmitter dry.
I ounted it up high on a mast and had pretty good results,but I really found
going with AM signal was much better. Also you are not limited by the
field strength on the AM bands. You are only limited by the performance of the
transmitter and the quality of antenna you use.
Yes it alot more work to lay ground radials and build a higher effient antenna but
I have found AM signal with part 15 far exceed that of the FM under part 15.
Part 15 FM is really good if you live in a city area in the country like I am
it cannot serve as a good station beacause you will not reach a listing audiance.
I will stick with AM part 15 because it works better for me.
My sugestion if you are going to do FM part 15. buy the best field strength meter
you can get. Take reading at 3 meters from your antenna on all sides of your antenna.
That means north,south ,east,and west. Make sure when you are 10 ft from your
antenna that you do not get a reading above 250uv. 10 feet not that far from your
antenna and you can get good readings. Make a log record the time ,date of when
you did this and keep a weekly log of this. Make sure you label what test equipment
you used to measure the field striength. The Good meters are FCC certified and also
make sure you have a calibration date on your meter.
Believe me if your power log is up to date and you can show the FCC you were trying
to keep good receords of your station radiated power this will be taken in
consideration when something comes up in question.
I know because I did this for large radio stations also.
Please know that field strength meter will not be cheap ,so realize what you are
getting into if you really want to keep in accordance with part 15.
Richard chart is very good.
Thanks
Originally answered a question from Louislau about his question about AM and FM.
Here's the thing...I'm in Canada and I forget about the difference between here and the US. Here in Canada FM is the way to go and here's why. First of all, I grew up with AM radio. I have an AM transmitter here(the spitfire) which works good and I gave a review of this on an earlier post.
I miss AM radio. But, AM never was in the past so full of electrical noise like it is now. And those compact florescent bulbs will be the death of AM in you house. If you have a radio plugged in to a/c AM is unlistenable...even the 50,000 watt local stations can't get clean reception if your surrounded by hydro. When there's a power outage..WOW!...great AM!!
Now for the technical details...in Canada the BETS-1 rules for unliecenced use for AM&FM differ from the US. It's better here. For FM, it's 100uV/m at 30 meters(100yds) from the antenna. So at 100 yds. away there's still a good signal for quite a distance still beyond that. This is enough to cover a whole small town or a decent size neighborhood like where I am in Toronto to get to a lot of residences...with a clean, high fidelity, noise free signal. As Artisan radio has pointed out on a receiver like a car radio or hi-fi receiver with sensitivity of under 2.5 uv a listenable signal can be heard a Kilometer to a mile away! And FM gets into houses and apartments a whole lot better because FM goes where AM doesn't. Just go into a store in a mall and see if there's any AM reception and then try FM and take note.
Now for AM...BETS-1 says not 100mw into final but here it's field strength...250uV/m at 30 meters(100yds).
More signal strength than FM...But...if you want to get more coverage than the indoor length of wire and water pipe ground you have to be fortunate enough to own your own property where you can install the outdoor set up...loading coil, 10 foot mast, and dig up the lawn to bury long wires in the ground. And hope someone doesn't steel or vandalize your antenna. And keeping in mind that AM doesn't go where FM does. Anywhere past a few houses away from you the signal will be weak in any house or building and no one will listen through the noise. Especially if using just indoor set up. I realized that transmitting on AM wouldn't get me any listeners, no one listens to AM or can't in their apts. or houses. Also with your HI-FI go to AM and see how it sounds.
One of the station Id's I have is a bit about now you have the music you grew up with in noise free good fidelity. And at night....forget it!! your station won't get through the interference.
A transmitter here in Canada also has to be tested and approved by Industry Canada to even be able to legally be used.
Only 2 transmitters are...Decade and Wholehouse.
The decade is set to BETS-1 and the wholehouse 3 is great! with extended antenna not stock, it get's the field strength allowed here nicely. IC certification # is on product.
The CCrane maybe...doesn't have IC certification.
Kits can't be Certified because it's subject to the builder.
In conclusion, in Canada You have enough allowable signal strength on FM to go the better way.
Only disdvantage is on AM there's way more space on the dial to go while FM is very crowded especially in southern Ontario.
Mark