what to knoo

It depends on how far from the antenna you are getting that reading.

Good car radios have sensitivities (their ability to hear signals) of under 2uv - and you'll get some quieting with that.  But it takes a field strength of about double and a bit that to induce a 2uv signal (assuming a 1 meter antenna).  So you require a field strength of around 4-5 uv/m to hear a signal.

If the legal field strength limit is 250uv/m at 3 meters, then you can do the calculations to determine at what range (line of sight to the antenna) you can expect to receive a signal on that car radio.

At 6 meters, you'll have a field strength of 125uv/m.  At 12 meters, 62.5 6v/m.  Etc.

So at 96 meters, you'll have a field strength (again, line of sight) of about 7.8uv/m and at 192 meters, just a little under 4uv/m.  That corresponds to a range of between 315-630 feet, with quieting, maximum.

You should be able to hear your signal a bit further if you're willing to accept some noise.  And a longer car radio antenna will get you even more range.  However, any obstructions between your transmitter antenna and your car radio antenna will degrade the field strength, and you'll get less range.

You should also recognize that the typical consumer radio will have a sensitivity much less than a car radio (less selectivity as well, that is, the ability to reject strong signals on adjacent frequencies).  So your range will be less there as well.

It doesn't matter what kind of antenna you have at the transmitter side, this is the kind of range(s) you can expect if it produces a legal field strength.  You're really limited at the transmitter side.

On the receive side, a potential listner can do a few things, particularly in the home.  You can put up an outside antenna that is directional and point it at the transmitter.  You can invest in a very sensitive FM tuner (some of the older, vintage ones have incredible sensivity and selectivity).  But this would not be a casual listener, as these options will cost a bit of money.

After all these back and forth messages, I have come to believe that Luis wants a yes or no answer.

Yes you can or no you can't.

What we have done is pile detail containing many "if this than that" and "unless this not that" kind of complicated suggestions, only managing to confuse the situation.

My attempt to simplify the answer is to say... Luis, "maybe."

I think I can simplify my answer, although I believe it was important to show the math and physics behind the ranges stated.

It doesn't matter what antenna you use for FM.  If you stay within the Part 15 legal field strength limit, you will get 100-200 feet range to an ordinary consumer radio, and upwards of 600-800 feet range to a car radio, depending on its sensitivity.  That's it.  You won't get a mile range, or 5 miles range, and be legal.  I believe that those facts have been reiterated several times and I don't know how much clearer they can be stated.

If he wants upwards of a mile range or even a bit more, Luis should look at Part 15 AM or Carrier Current.

I'll try to answer this more accurately. 0.0000000675uV/m at 3 meters from antenna is WAY lower than the legal limit.

In fact 0.0000000675uV/m is so small that it's practically non existant.

But your question dosen't specify whether the 0.0000000675uV/m is at 3 meters from the antenna or not.

Maybe you can ask the question again and be more specific.

Mark

The unit of measure "UV/M' used in the opening post might have been incorrect.

If the correct unit of measure is watts, then the value 0.000 000 0675 watts (67.5 nanowatts) is getting close to the power needed by a center-fed 1/2-wave dipole to produce an FCC-compliant 250 µV/m field 3 meters from that dipole, in free space.

Actually 67.5 nanowatts is about 5.9X more power than needed to produce a 250 µV/m field 3 meters away from that dipole.  It would produce a peak field of about 607 µV/m three meters away from that dipole.

Maybe the bigger issue here is that very few unlicensed "Part 15" operators have the test equipment needed to accurately measure these powers and/or field strengths.  So if one wants to comply with Part 15 FM, it might be better to buy an FM transmitter with its integrated antenna that is FCC-certified as compliant with Part 15, and use it without modification.

We often hear the advice of ensuring compliance by using certified transmitters, but advice from the manufacturers can point in another direction.

At C.Crane's FAQs page for their FM transmitter it says...

"In open environments with minimal radio noise, the range of an FM transmitter can be easily increased by attaching a length of wire to the telescoping whip antenna of the FM transmitter. In our experiment, we attached a 31-inch length of wire to the whip antenna of an FM transmitter using an alligator clip (Any wire will work. Any clip that secures the wire to the transmitter's antenna will work)."

There's even a picture of a clip-lead attached to the telescopic antenna.

The manual for my Wholehouse 2.0 says "The higher and longer an antenna is the better the transmission will be."

My Scosche FMT4/FMT4R Transmitter includes settings for 87.7 and 87.9 MHz, frequencies outside of channels recognized in the rules.

All three of these are certified.

In Reply #8 above, Carl Blare posted: We often hear the advice of ensuring compliance by using certified transmitters, etc.

UNMODIFIED FM transmitters and their supplied antennas that are FCC-certified under Part 15.239 have a good chance of being compliant with Part 15.239.

Regardless of the source of the advice in the first two two quotes given in Mr Blare's Reply #8, it requires a change with respect to the supplied transmit antenna for those devices -- to a configuration that almost certainly was not the antenna configuration that was tested and submitted to prove FCC compliance for those devices.

Such antenna changes can produce increased fields/coverage from those devices, which may exceed the limits of Part 15.

A logical conclusion from historical FCC citations shows that unlicensed operators in the AM/FM broadcast bands wanting to comply with Part 15 are themselves responsible to do so, regardless of the "certified" hardware, its antenna configuration, and/or the frequency it uses.

hey how about carrier curent am? how much power could iuse?and whats a good range from a carrier am transmiter?

Carrier Current is a wonderful Part 15 method of reaching out on the electric lines to homes in the area.

The one and only company that makes and sells equipment for carrier current is Radio Systems, and by contacting them they will be able to describe how to set it up and how far it will reach.

http://www.radiosystems.com/lowpower.html

but will they allow me to use it in my church or my studio??

luisrosado, the happy good news is that carrier current is absolutely allowed under FCC Rule # 15.221.

I myself have built a carrier current radio station using old equipment that is no longer sold, but which I bought second-hand and repaired.

One of our members, station8, has just compiled a whole batch of documentation about carrier current, which is posted at

http://thealpb.com

But you will need new gear, so contact Radio Systems.

I spoke to radio system they told me is not legal to use the transmitter at my church