a few part 15 questions....

[pianoplayer88key]

I have a few part 15 related questions concerning multiple frequencies....

First off... when you guys claim "1/4 mile range", "1 mile range", etc... what exactly does that mean? Is it:
A: how far your signal gets with full quieting (i.e. city-grade signal enough to punch through powerline noise / etc) while you're inside a Faraday cage with a crystal set with its antenna disconnected and a high-power-draw loudspeaker hooked up with its amplifier turned off
B: using a military-grade communications receiver on a boat in the middle of an ocean, with the transmitter the specified distance away, your receiving antenna is a full-wave (or longer) tuned antenna, and you have to use a QRSS spectograph analysis to detect any hint of a signal
C: something in between those two extremes (please specify)


Now, for the main questions....

Under each of the FCC parts cited below, how far does the signal typically go? FYI I'm near Mt Helix area east of San Diego, CA, and there isn't nearly as much manmade noise here as there is in L.A. (For example, on a decent portable AM radio in the daytime, 970 from Coachella and 980 from Los Angeles are at the limits of detectability/identifiability without resorting to the Select-A-Tenna.) Assume I'm using an average to good portable without the select-a-tenna, and want to know its range to where yes there definitely is noise, but the signal is still 100% copyable.
For the ones which specify field strength requirements, what's the typical transmitter power to use when using A: a 1/2-wave antenna, B: no external antenna (just the internal wiring on the device serves as the transmitting antenna, or it's entirely self-contained within the structure of the device)?
In most cases, assume audio is voice/music, amplitude modulated (unless FM is better for a particular application). Monaural sound and a 4.4kHz high frequency cutoff should be assumed. (Optional: also figure stereo, 15kHz audio, if it would significantly affect range)
For the parts that specify field strength based on the frequency of the device, like a couple sections of 15.209, or 15.221, do you get more range at lower frequencies or higher frequencies?

Part 15.209
175kHz: 2400/175 = 13.714μV/m @ 300m (middle of 160-190 band, as alternative to 15.217)
520kHz: 24,000/520 = 46.15μV/m @ 30m (alternative to 15.219 or 15.221 ; other frequencies & their field strengths below:
660kHz = 36.36μV/m
880kHz = 27.27μV/m
1500kHz = 16μV/m
1570kHz = 15.3μV/m
1610kHz = 14.9μV/m
1680kHz = 14.3μV/m

Part 15.217
160-190kHz: 1 watt, 15 meter antenna (rules are a little more specific but you guys should understand what's meant)
Operating frequency would be likely 175kHz

Part 15.219
510-1705kHz: 100 milliwatts, 3 meter antenna (NOTE: 3 meters is 118", not 108")
Likely operating frequencies: 520, 660, 880, 1500, 1570, 1610, 1680

Part 15.221
525-1705kHz: 15uV/m @ 47715/kHz meters. Possible frequencies:
560kHz: @ 85.2m
660kHz: @ 72.3m
880kHz: @ 54.22m
1500kHz: @ 31.8m
1570kHz: @ 30.4m
1610kHz: @ 29.64m
1680kHz: @ 28.4m

15.221b: how does this work? Do they measure it from the farthest point of campus property away from the transmitter? BTW I share a property line with an elementary school, does that mean I could operate under this section by mounting the transmitter on the corner of the fence, assuming i had the school's permission, or mounted the structure on my side of the fence?

Part 15.225
13.553-13.567MHz = 15,848μV/m @ 30m
(13.410-13.553 & 13.567-13.710 = 334μV)
Operating frequency would be 13.56MHz
How much less in dB is 334μV than 15848μV in this case?
for wideband audio (if you're figuring it) assume it would not exceed the 14kHz limit. (whether it's 7 kHz stereo or 14 kHz mono, or is it possible to have 14 kHz stereo SSB?)

Part 15.227 and 15.235
26.96-27.28MHz & 49.82-49.9MHz = 10mV/m @ 3m
TX Power with 1/2 wave Antenna? also with no antenna?

Part 15.239
88-108MHz = 250μV/m @ 3m
TX Power with 1/2 wave Antenna? also with no antenna?

Part 15.249
902-928MHz, 2.4-2.4835GHz, 5.725-5.875GHz = 50mV/m
24-24.25GHz = 250mV/m
TX Power with 1/2 wave Antenna? also with no antenna?

Yeow! That's a mouthful/earful/whatever you wanna call it

Ok, ok, so here's another one maybe David Eduardo could answer it...
Is 10mV/m the minimum signal level for full quieting in an office or factory in, say, downtown Los Angeles, or what is that 10mV/m minimum signal (on AM broadcast) you refer to? And what's the equivalent for rural, less noisy locations?

Richard Fry, I understand you frown upon part AM transmitters mounted atop a tall metal pole, basically. What about AMs mounted on the ground with a ground radial system? Also would that radial system need to be buried, or could I just lay it across the ground?

 

[LibertyNT]

I just go off on how far i can get it without it completely fading out.
With a Walkman and a Car Radio and a S350 DL

Personally I would Bury the wires.. But i don't think you'd have to

 

[rfry]

I have a few part 15 related questions concerning multiple frequencies.

Comments on some of them...

For the ones which specify field strength requirements, what's the typical transmitter power to use when using A: a 1/2-wave antenna etc

For the upper end of the AM broadcast band the maximum legal field intensity under 15.209 is produced by an effective radiated power (ERP) on the order of 10 nanowatts (0.000 000 01 watts), regardless of the radiator used.

For the parts that specify field strength based on the frequency of the device, like a couple sections of 15.209, or 15.221, do you get more range at lower frequencies or higher frequencies?

This depends on the local noise level, and of course, the amount of interference from licensed stations. Generally the noise level is worse at lower frequencies, but whether of not the higher field strength allowed for lower frequencies can give better reception will depend on the receiving system, noise and interference.

Part 15.239 88-108MHz = 250μV/m @ 3m. TX Power with 1/2 wave Antenna? also with no antenna?

The maximum field is generated by a 1/2-wave dipole radiating 11.43 nanowatts (0.000 000 011 43 watts). Using no antenna would radiate no power, except for incidental radiation from the transmitter itself, depending on how well it was shielded and connected to r-f ground.

Is 10mV/m the minimum signal level for full quieting in an office or factory in, say, downtown Los Angeles, or what is that 10mV/m minimum signal (on AM broadcast) you refer to? And what's the equivalent for rural, less noisy locations?

Terman's Radio Engineers Handbook (1943) shows the following as "Required Field Strength" for acceptable AM broadcast station reception in areas of their primary coverage:

City business or factory areas.... 10-50 mV/m
City residential areas...... 2-10 mV/m
Towns (2,500-10,000 population)..... 2 mV/m
Towns (under 2,500 population)..... 0.5 mV/m
Rural -- all areas during winter, northern areas in winter.... 0.1-0.5 mV/m
Rural -- southern areas during summer..... 0.25-1.0 mV/m

Of course the electrical noise level in the home was much less in 1943 than it is now (SCR light dimmers etc).

Note that a legal system using 15.209 could not produce even the minimum fields shown above unless well within 30 meters from the radiator. According to the FCC, using 15.219 should give roughly comparable results.

Richard Fry, I understand you frown upon part AM transmitters mounted atop a tall metal pole, basically. What about AMs mounted on the ground with a ground radial system? Also would that radial system need to be buried, or could I just lay it across the ground?

All I have ever posted about this subject is that elevated Part 15 AM systems almost always have long conducting paths to r-f ground, which mean that functionally they are non-compliant with 15.219. It doesn't matter to me if anyone uses this configuration -- that's up to each user. My purpose is to inform, not to judge.

As for radials, recently John Reed at the FCC OET e-mailed me this comment (quoted with permission):

"If you attach your ground lead to a drainpipe, billboard, or other structure, that structure becomes part of the ground lead and is included in the 3 m limit. Similarly, if you install a ground plane or otherwise change the ground efficiency."

Everyone is free to use or reject this information as they see fit.

//

 

[Hamilton]

This is the official FCC policy:

The 3-meter combined length specified in Section 15.219(b) refers to the length of all radiating elements. Attaching the ground lead to an unshielded radiating object, or the addition of a ground screen, will cause the effective length of radiating elements to exceed 3 meters, in violation of Section 15.219(b).

 

[Bongwater]

I have a few part 15 related questions concerning multiple frequencies....

First off... when you guys claim "1/4 mile range", "1 mile range", etc... what exactly does that mean? Is it:
A: how far your signal gets with full quieting (i.e. city-grade signal enough to punch through powerline noise / etc) while you're inside a Faraday cage with a crystal set with its antenna disconnected and a high-power-draw loudspeaker hooked up with its amplifier turned off
B: using a military-grade communications receiver on a boat in the middle of an ocean, with the transmitter the specified distance away, your receiving antenna is a full-wave (or longer) tuned antenna, and you have to use a QRSS spectograph analysis to detect any hint of a signal
C: something in between those two extremes (please specify)


Now, for the main questions....

Under each of the FCC parts cited below, how far does the signal typically go? FYI I'm near Mt Helix area east of San Diego, CA, and there isn't nearly as much manmade noise here as there is in L.A. (For example, on a decent portable AM radio in the daytime, 970 from Coachella and 980 from Los Angeles are at the limits of detectability/identifiability without resorting to the Select-A-Tenna.) Assume I'm using an average to good portable without the select-a-tenna, and want to know its range to where yes there definitely is noise, but the signal is still 100% copyable.
For the ones which specify field strength requirements, what's the typical transmitter power to use when using A: a 1/2-wave antenna, B: no external antenna (just the internal wiring on the device serves as the transmitting antenna, or it's entirely self-contained within the structure of the device)?
In most cases, assume audio is voice/music, amplitude modulated (unless FM is better for a particular application). Monaural sound and a 4.4kHz high frequency cutoff should be assumed. (Optional: also figure stereo, 15kHz audio, if it would significantly affect range)
For the parts that specify field strength based on the frequency of the device, like a couple sections of 15.209, or 15.221, do you get more range at lower frequencies or higher frequencies?

Part 15.209
175kHz: 2400/175 = 13.714μV/m @ 300m (middle of 160-190 band, as alternative to 15.217)
520kHz: 24,000/520 = 46.15μV/m @ 30m (alternative to 15.219 or 15.221 ; other frequencies & their field strengths below:
660kHz = 36.36μV/m
880kHz = 27.27μV/m
1500kHz = 16μV/m
1570kHz = 15.3μV/m
1610kHz = 14.9μV/m
1680kHz = 14.3μV/m

Part 15.217
160-190kHz: 1 watt, 15 meter antenna (rules are a little more specific but you guys should understand what's meant)
Operating frequency would be likely 175kHz

Part 15.219
510-1705kHz: 100 milliwatts, 3 meter antenna (NOTE: 3 meters is 118", not 108")
Likely operating frequencies: 520, 660, 880, 1500, 1570, 1610, 1680

Part 15.221
525-1705kHz: 15uV/m @ 47715/kHz meters. Possible frequencies:
560kHz: @ 85.2m
660kHz: @ 72.3m
880kHz: @ 54.22m
1500kHz: @ 31.8m
1570kHz: @ 30.4m
1610kHz: @ 29.64m
1680kHz: @ 28.4m

15.221b: how does this work? Do they measure it from the farthest point of campus property away from the transmitter? BTW I share a property line with an elementary school, does that mean I could operate under this section by mounting the transmitter on the corner of the fence, assuming i had the school's permission, or mounted the structure on my side of the fence?

Part 15.225
13.553-13.567MHz = 15,848μV/m @ 30m
(13.410-13.553 & 13.567-13.710 = 334μV)
Operating frequency would be 13.56MHz
How much less in dB is 334μV than 15848μV in this case?
for wideband audio (if you're figuring it) assume it would not exceed the 14kHz limit. (whether it's 7 kHz stereo or 14 kHz mono, or is it possible to have 14 kHz stereo SSB?)

Part 15.227 and 15.235
26.96-27.28MHz & 49.82-49.9MHz = 10mV/m @ 3m
TX Power with 1/2 wave Antenna? also with no antenna?

Part 15.239
88-108MHz = 250μV/m @ 3m
TX Power with 1/2 wave Antenna? also with no antenna?

Part 15.249
902-928MHz, 2.4-2.4835GHz, 5.725-5.875GHz = 50mV/m
24-24.25GHz = 250mV/m
TX Power with 1/2 wave Antenna? also with no antenna?

Yeow! That's a mouthful/earful/whatever you wanna call it

Ok, ok, so here's another one maybe David Eduardo could answer it...
Is 10mV/m the minimum signal level for full quieting in an office or factory in, say, downtown Los Angeles, or what is that 10mV/m minimum signal (on AM broadcast) you refer to? And what's the equivalent for rural, less noisy locations?

Richard Fry, I understand you frown upon part AM transmitters mounted atop a tall metal pole, basically. What about AMs mounted on the ground with a ground radial system? Also would that radial system need to be buried, or could I just lay it across the ground?

It's figures, facts and nagging questions like these that create the reason for medical marijuana...just to keep your head from exploding....

 

[Hamilton]

Here are some plain English responses to some:

I call range the distance at which you can get a listenable signal with a good quality (auto) radio, there may be a little static, but the signal will be comfortable to listen to.

15.219 I can tell you the higher freqs tend to be better.

15.221 Actually it would be the closest point, you can allow this limit to be exceeded outside your border.

Ground radials can just be laid on the ground.

 

[cgbrock]

I'm ignorant. Is a "ground screen" different than "buried ground radials"?

 

[Hamilton]

Seems what they mean by "ground screen" is an above ground (not in the dirt) metal radiator of some sort.

 

[Neil E.]

Seems what they mean by "ground screen" is an above ground (not in the dirt) metal radiator of some sort.

How about we don't ask for a clairification on this? It would also be best that we stop speculating on this among ourselves.

Neil

 

[phatdaddy]

Here is something to keep in mind regarding ground systems.....A ground radial system's function is to gather the earth currents induced by the antennas near field and return said currents to the transmitter's common point, thus completing the antenna "circuit". If the ground system is mounted above the earth, the RF return currents flowing through the radials back to the transmitter common point have the propensity to radiate because they are not shielded by being buried in the ground. If the ground radial system is buried in the ground, any radiation created by the ground return currents is shielded by the surrounding earth and does not contribute noticeably to the system's overall signal strength. It's time to stop whipping this dead horse and move on.

The bottom line on station inspections is this....it's up to the individual inspector and how he interprets the latest FCC inter-office memos and the Part 15 rules as they apply to your particular installation. He will ultimately have to make the decision "is this operator trying to game the system or is he trying to stay within the intent of Part 15"? The inspector's answer to this question will determine whether you get a citation or not.

In other words...use a little common sense. If you have your rig on top of a 50' telephone pole with an unshielded / unfiltered ground wire running down the length of the pole, it doesn't take a broadcast engineer to figure that you're trying to game the system and you'll most likely get a love letter from the FCC field office. Is your rig ground mounted with a buried ground system? If so you probably won't get out for two miles (which wasn't the intent of Part 15 in the first place), but you probably won't get a citation either.