Hello everyone. A newbe here to the forum. The FCC rules state that one can leaglly operate a station that covers only a couple hundred feet. My Ramsy FM100b covers about 6 1/2 block circumference. I have at my disposal a one watt upgrade that I have not installed and was wondering since the FCC does not license any stations under 10 watts if it would be safe to do so. I don't want them kicking my door down. This is just a hobby. Not much more than four to six hours of operation once a week... on a weekend... once in a while will run eight. Country/rock variety from pivate collection with time, temp, any nessesary alerting and some PSA's. Have always maintained a private studio for many years before and after 10 years of pro broadcasting. I have aquired a real nice pair of Russco cue masters with Gray Research tone arms. An ITC PDII, two Audi-cords and so on. Dual CD player all through a 10ch console using an AKG condenser mic.
This question was also posted in another thread and I answered it. Here's a copy of what I wrote:
Hello, Paul, and welcome to the forum.
The question of the legality of Part 15 FM operation comes up often and the answer is not simple. The difficulty for a hobby broadcaster is that the limit on FM transmission is based on field strength at a distance (250 uV/m maximum at 3 meters) which is sensible from a technical perspective but is virtually impossible for the hobbyist to measure. Though this field strength relates to the transmitter power, the amount of power which produces this field strength is very low, too low to measure without specialized equipment.
The hobbyist is left with another gauge of compliance which is approximate but which is practical. The FCC has published that a compliant FM operation will produce a range of approximately 200 feet but they did not mention the type of receiver to use. The receiver and antenna greatly affects range.
Many of us interpret this to mean the range would be 200 feet on a portable receiver with greater range obtained with a car radio due to the car radio having a good antenna and a sensitive receiver. Estimates are about 600 to 1000 feet with such a receiver but this is not well documented and has no legal basis.
We can either use a transmitter which is FCC certified or use one which is not and adjust the range (usually by changing the antenna length) to the above guidelines.
A 1 watt amplifier will certainly produce a signal well above the limits and would be risky.
It is regrettable that there is not a better answer since an accurate measurement requires a very expensive field strength meter, yet many of us have used the range estimate and have been on the air for years without trouble. If you make a reasonable effort to achieve this range you should be OK.
Neil
If I'm not mistaken, the FCC states that the range would be 200 feet to an 'ordinary' receiver, whatever that is. As Neil points out, many (including myself) take that to mean a common, household receiver. Car receivers have much greater sensitivity (allowing the range to be greater) and perhaps more important, far greater selectivity (the ability to filter out adjacent channel interference). The common household receiver has poor selectivity, and strong stations in a crowded FM band will bleed over into your frequency, greatly reducing range as well.
Thanks for the respose!... and you know, I kinda thought about that. But still, I do have the transmitter hooked to an GP antenna with the appropriate cable and frequency range applied. cable is cut at 26 feet... antenna is at 22'. Should I discontinue its use and just run off the factory whip? Paul
There are different qualities of common portable receivers......Sangeans are better than average portable recievers as compared to the cheap boombox type. So are older radios like the GE super. So your mileage will vary.
On video of Tom Web at wholehouse demonstrating the range of the wholehouse 2 certified transmitter operating as it comes out of the box on the 50 yard line of a football field with a wind up eton(grundig) radio walked to the end zone 150 feet away still had a perfect signal and I know he could have kept walking back a lot farther before he lost it. And that wasn't the best portable around.
All car radios are much better but unless you are stationary in the coverage area you move in and out of the signal area to fast. So, for the "part 15" hobby it's how you do on a home or portable radio that's important.
Fortunataly, here in Canada I'm not in the jurisdiction of the FCC and the rules here are less strict and allow for greator FM coverage with it's superior audio quality, no electrical interference, and the ability to get signal into places AM can't.
Mark
Paul,
You could use a coax fed antenna mounted anywhere. There are no restrictions on this. What you need to be aware of is that any antenna arrangement needs to produce a field strength less than the limit. Again, this practically means limiting the range of the signal.
Neil