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Keep in mind the real rules for Part 15 FM

M

Mid West Clubber

Guest
Im not on here to be smart... i used to run RF my self,.,, but those of you that are getting like a quarter mile to one mile from FM,, you are illegal and could get caught,,, its easier for the FCC to find a part 15 than it is to find a 5000 watt pirate. I know a guy who thinks he is legal using a Ramsey 25 B, but he gets out a quarter mile, so its not legal... the maximum for a REALLY maxed out TX is the 40 DBU contour ends at 10 feet, and may drift up to 200 feet detectable... My Sirius and Ipods have Part 15 TXs I have bought for them, and they barely trvavel to the antenna at the back of the car,, and they still have static. SO be safe and be careful out there... MWC REGARDS.... Im definately pro part 15 and even pro pirate,, I just dont want anyone getting busted.. My own brother radiates 20 watts on AM 530,, cant tell you were,, and the signal does indeed fade out 2 houses down,, but its still illegal, and he wont listen to me.
 
I have a friend in the same situation. He has one of the Ramsey kids and in the car i can pick it up just over 3 miles away. I was lucky enough to pick up a Potomac FM field intensity meter and I plan on doing a surprise visit outside his house. I know when he sees what the meter reading is that it will give him the required slap on the side of the head to realize what he's doing is not smart.

It's pretty much a given if your Part 15 FM is going much farther than your own yard than it's probably not legal.
 
I used to have a Sirius Visor unit years back when they had supper charged Modulators,, and it was able to be picked up a half mile away.. Not far enough to really get any listeners or anyone to notice,,, but far enough for the FCC to notice... These days I broadcast exclusively on the internet cause I think part 15 is a waste,, its not powerful enough to get noticed and be noticed at the same time.. Part 15 isnt even considered an intentional radiator. Im not knocking anyones hobby ,, Part 15 AM can get out to maybe detectable at one mile with a Range Master,, that could build an audience if its promoted and the exact right format is used,, but technically even part 15 AM will only go 2 city blocks....

Part 15 fm other than personal use up to 10 feet is all together useless.
 
Maybe you mean that Part 15 AM and FM are not considered to be broadcasting, which is true. They are certainly considered to be intentional radiators.
 
If 100uV/m is required to get just the slightest possibility of a hint of a trace of a QRSS CW carrier on FM, then in my opinion that is one extremely deaf radio! I don't know what the natural (non-manmade) noise floor is in the FM band, but I think receivers should be sensitive enough to detect audio and trip the stereo decoder to within less than about 6dB or so of that level, assuming you're using the supplied antenna.
Being closer to reality, my Tecsun PL-380's manual states an FM sensitivity spec of less than 3 microvolts at 30dB SNR. If my assumption that approximately every halving of field strength voltage approximates to a reduction of 6dB, then I would expect a signal to reach the noise floor (0dB) at around 93.75 nanovolts or so. In practice, due to line-of-sight and interference issues, and a broken off antenna segment, it doesn't seem to be that sensitive.
Even if an FM receiver only had a sensitivity of about 1 microvolt, I would think the signal could still be heard at almost a half mile or so, although by then a ham might report it as maybe a S1 or S2. (That's if my guess that doubling the distance means halving the field strength voltage is correct.)
Now, if my assumption that electric field strength voltage halves with a doubling distance is wrong, I would like to know.
 
tfcwings said:
...Now, if my assumption that electric field strength voltage halves with a doubling distance is wrong, I would like to know.
Click to expand...

That assumption is correct for far-field radiation in free space, but not necessarily over a terrestrial path.

The bigger consideration here is that once the r-f signal in an FM receiver falls below the threshold of its AM limiters, then the audio S/N drops quickly. So the audio noise in a receiver rated for 3 µV* at 30 dB S/N (in monaural only, no doubt) does not have a linear change with a change in r-f voltage.

Probably most people wouldn't listen very long to audio with an S/N of 6 dB, and that could occur in your Tecsun PL 380 or a similar receiver for r-f input levels of less than 1 µV or so.

* That is the sensitivity spec at the r-f input terminals of the receiver, not the field intensity of the arriving FM signal. A short, monopole whip antenna with a poor r-f ground such as used on these Tecsun radios has a rather high "Antenna Factor." This means that the field intensity in µV/meter arriving from the FM station needs to be quite a bit larger than the sensitivity spec of the receiver.

RF
 
Do what you want,,, Ive done it myself at much higher power,,, both legal,, and not so... Its just that I read that Part 15 must die down to 40 DBU at 10 feet... its on the fcc site.,.. Yeah I know the FCC sucks,, but thats what it says.
 
40dBu in field strength is 100 uV/m--right? 10 feet is about two inches more than 3 meters, which is the distance from the antenna at which a maximum field strength of 250 uV/m is allowed. This would be the 48 dBu level. The FCC seems to be saying that the actual field strength is expected to be 8 dB less than the allowed limit. The manufacturer will have to allow some margin to be sure not to exceed the limit, but 8 dB is a bit much.

If 100 uV/m is the actual field strength of a certified transmitter at 3 m, the 3 uV/m level should be at around 100 m.
 
In my opinion, the levels allowed for intentional radiators for unintentional radiators are way too similar.
For an unintentional radiator, I would prefer that the maximum signal allowed be about 90dB or more below the lowest naturally-occuring noise level (whether it's atmospheric noise in the wintertime when there's no thunderstorms within several thousand miles, or some other type of natural noise), when measured on the INSIDE surface of the exterior cover of the device/cable/whatever is radiating the unwanted RF.

As for an intentional radiator... What could I use to cover an area like this (or at least the marked property) with a rock-solid signal from a single non-directional transmitter? The property boundary is marked by the four light green corner angle lines, and the would-be transmitter site is marked with a light blue arrow. There's a scale in the lower left, but the property dimensions are about 250 feet east to west, and about 90 feet north to south. Would it be possible to have a signal that overloads a Tecsun PL-380, PL-310, Grundig G8, or other comparable radios within about 25 feet of the transmitting antenna (with a reading of about 98,25 or so)? Or, what about having it strong enough within the property to be desensing the aforementioned DSP based portable radios, indicating 50,00 +/- 100kHz of the frequency, at the farthest point on the property away from the transmitter, or at least indicating something like 87,25 to 90,25 there? Or is that level not possible? Also would part 15 FM, AM, or ~13.56MHz be better for maximum legal coverage?
 
a part 15 FM should easily cover that.
My FM goes about 300 useful feet.
I've found mine starts to fade about 172 feet away on one direction
about 300 ft in the other.
On the 172 side it clears up some a 200 feet then abruptly cuts out at 472 feet.
The farthest Ive gotten my station was 1080 feet,
but this was on a strange rainy day where my signal
was unusually strong, and it wasn't really listenable
at that distance just noticeable.
 
tfcwings said:
In my opinion, the levels allowed for intentional radiators for unintentional radiators are way too similar.

For an unintentional radiator, I would prefer that the maximum signal allowed be about 90dB or more below the lowest naturally-occurring noise level (whether it's atmospheric noise in the wintertime when there's no thunderstorms within several thousand miles, or some other type of natural noise), when measured on the INSIDE surface of the exterior cover of the device/cable/whatever is radiating the unwanted RF.
Click to expand...

That is a physical impossibility.

All electronic devices generate noise, even passive devices like resistors which generate thermal noise. Except for a crystal radio, RF devices must contain an oscillator of some kind (i.e. generate an RF signal at a high enough to function) for a circuit to work properly. And even the diode in a crystal set will generate some noise, probably way higher than you're talking about.

Proper shielding (rare in consumer electronics, I'll grant you) will reduce noise from these devices, but even then, it's not perfect.

I agree that most electronic equipment generates too much noise, but don't waste your breath complaining to the FCC about it. The Unwashed Masses don't care if they can't hear anything but a loud-and-clear AM station (if they're listening to AM at all), and there are probably hundreds of millions of borderline (at best) devices like PCs and CFLs out there in the world.

Really, only a few hundred thousand people out of 300 million care (mostly AM station owners and hams operating on HF). The average consumer's TVs and FM radios aren't being interfered with, and neither are their PCs or phones. So they don't care about noise on the AM band. The FCC won't respond until there is a complaint. It has happened in years past, especially about things like light dimmers interfering with AM radio, but I don't know about any recently.
 
Test lab reports for certified Part 15 FM transmitters are published on the FCC web site. Some manufacturers (including C Crane) have decided not to publish their test lab results, maybe to avoid unfavorable comparison to competing manufacturers. Manufacturers have the right to redact sensitive competitice information from the reports. Field strength has to be below the 48 dBu limit over the entire FM band. Some channels of a transmitter produce higher field strengths than others. The requirement not to exceed the 48 dBu field strength limit anywhere in the FM band can cause some channels to produce a fairly low output.

For units for which the field strength results have been published, I've seen measurements just below the 48 dBu limit, and other results even below the 40 dBu level. I now think that 100 uV/m, and even lower, is a possible field strength at 3 m for a certified Part 15 AM transmitter. Maybe that is why the FCC chose the 40 dBu signal level in its analysis.
 
The FCC won't respond until there is a complaint.

That is absolutly untrue. We had an instance in the neighborhood where I live where we had a faulty lightning arrestor on a power pole. Tampa Electric made one visit and incorrectly blamed a source in someones house. The noise by the way, obliterated the upper portion of the AM radio band 2 blocks away from the suspected source.

The only way we got Tampa Electric back out to solve the problem was sending an email to the Tampa Enforcement Office stating that it was impossible to hear AM radio in the neighborhood. Two days after the email, I received a call from Tampa Electric's Quality Assurance Department telling me that they would be back out and that "emails were flying all over the place."

Guess what? they fixed it. :)
 
druidhillsradio said:
The FCC won't respond until there is a complaint.
That is absolutly untrue. ... The only way we got Tampa Electric back out to solve the problem was sending an email to the Tampa Enforcement Office stating that it was impossible to hear AM radio in the neighborhood. Two days after the email, I received a call from Tampa Electric's Quality Assurance Department telling me that they would be back out and that "emails were flying all over the place."
Click to expand...

Just curious... wouldn't the email to the Tampa Enforcement Office be considered a complaint?

If so, had the Enforcement Office been working on the Tampa Electric problem before they received the email?

If not, it looks like the FCC needed the email (complaint) before they did anything, so maybe the statement you opened with is not absolutely untrue?
//
 
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