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Hello all,
There is a really interesting thread on this board under the title “FCC and the PART 15.219”. I believe many of the questions can be answered by reading the following excerpts from the FCC part 15 rules as revised Sept. 2005. To help you, I have copied parts below. They are not complete but cover the essentials.
Section 15.209 Radiated emission limits, general requirements.
(a) Except as provided elsewhere in this Subpart, the emissions from an intentional radiator shallHello all,
There is a really interesting thread on this board under the title “FCC and the PART 15.219”. I believe many of the questions can be answered by reading the following excerpts from the FCC part 15 rules as revised Sept. 2005. To help you, I have copied parts below. They are not complete but cover the essentials.
Section 15.209 Radiated emission limits, general requirements.
(a) Except as provided elsewhere in this Subpart, the emissions from an intentional radiator shall
not exceed the field strength levels specified in the following table:
Frequency Field Strength Measurement Distance
(MHz) (microvolts/meter) (meters)
_______________________________________________________________
0.009 – 0.490 2400/F(kHz) 300
0.490 – 1.705 24000/F(kHz) 30
1.705 – 30.0 30 30
30 – 88 100 ** 3
88 – 216 150 ** 3
216 – 960 200 ** 3
Above 960 500 3Section 15.215 Additional provisions to the general radiated emission limitations.
(a) The regulations in §§ 15.217-15.257 provide alternatives to the general radiated emission
limits for intentional radiators operating in specified frequency bands. Unless otherwise stated, there are no restrictions as to the types of operation permitted under these sections.Section 15.219 Operation in the band 510 – 1705 kHz.
(a) The total input power to the final radio frequency stage (exclusive of filament or heater
power) shall not exceed 100 milliwatts.
(b) The total length of the transmission line, antenna and ground lead (if used) shall not exceed 3
meters.
(c) All emissions below 510 kHz or above 1705 kHz shall be attenuated at least 20 dB below the
level of the unmodulated carrier. Determination of compliance with the 20 dB attenuation specification
may be based on measurements at the intentional radiator’s antenna output terminal unless the intentional
radiator uses a permanently attached antenna, in which case compliance shall be demonstrated by
measuring the radiated emissions.
Section 15.221 Operation in the band 525 – 1705The formatting for 15.209 got a little messed up but it is readable. I hope this helps.
Neil
Total posts : 45366by MRAM 1500 kHz
Yes, that thread has been through a few needles by now.
You have done exactly what I was preparing to do; cut out all but that which pertains to the AM broadcast band. Thanks for posting the excerps for those who have yet to read Part 15. I’ve read it enough times but it seems to take on different meanings depending on how you look at it.
A good example is the issue of RF grounds. Everyone seems to have heard a different interpretation. Some sound very convincing but the FCC has the final say when they show up. Of course, from what we’ve seen even they have differing opinions on the subject.
I was pleased to see that you interpret 15.209 as I have, that you can use any power level and any antenna you desire IF you can insure that your field strength does not exceed the calculated value specified by that rule. I’d love to try a longer vertical with a nice ground system and see if the coverage pattern smooths out. Maybe an antenna like that new Kenstar low profile that was recently approved for commercial AM stations.
I’d put up with a little less signal for one that covers more evenly.
Bob
Total posts : 45366[quote=mram1500]
I was pleased to see that you interpret 15.209 as I have, that you can use any power level and any antenna you desire IF you can insure that your field strength does not exceed the calculated value specified by that rule. [/quote]
__________Part 15 AM field strength 30 meters from the tx antenna permitted by 15.209 ranges from about 44 uV/m at 540 kHz to 14 uV/m at 1,700 kHz.
BUT the field strength generated at that distance by a Part 15 system under 15.219 is much higher than that (see my following analysis).
+ + +
Below are some calculated values for field strengths at several distances from the Part 15.219 compliant r-f system described there.
These calculations are based first on a NEC-2 analysis to determine the FCC efficiency for the antenna, and then using that value with the FCC’s propagation curves for the frequency and ground conductivity, to determine the distances to the contours shown. This is a proven process which applies even at these low powers.
DATA:
Frequency = 1700 kHz
Applied Power = 80 milliwatts (~output power of Part 15 AM tx)
Radiator = 3-meter total length including the conducting path from the tx chassis to the ground plane (antenna is ground-mounted)
Antenna System RF Resistance, Loading Coil plus Ground = 10 ohms
Ground Conductivity = 8.0 mS/m (typical value)
Radiation System FCC Efficiency = 21.12 mV/m at 1 mile for 1 kW appliedRESULTS:
Field Strength > Distance
2 mV/m > 0.09 miles (good signal)
1 mV/m > 0.18 miles (fair)
0.5 mV/m > 0.34 miles (noisy)
0.05 mV/m > 2.5 miles (very noisy)This information should assist anyone wanting to know the approximate coverage capabilities of a legal Part 15 AM r-f system, as described.
Total posts : 45366Rich and all,
Thanks for running the simulation. I have wondered how the two “rule modes” compare.
From your table there is a tremendous difference. Though your table doesn’t include 30 meters (.019 mile) one can infer that the field strength is much greater than 14 uV/m, and that a decent signal will exist at about 1000 feet from the antenna.
Too bad we have the antenna limitation. For example cell phones operate in the hundreds of mW. range (variable with a max about 600mw if I recall) but do so with a decent antenna and can be heard by the tower for miles. Same for 250 mW 2 meter ham handhelds.
Neil
Total posts : 45366(radio8z): Too bad we have the antenna limitation. For example cell phones operate in the hundreds of mW. range (variable with a max about 600mw if I recall) but do so with a decent antenna and can be heard by the tower for miles. Same for 250 mW 2 meter ham handhelds.
___________Radiator efficiency is part of it, but other issues also are in play. Electrical noise is much lower in the cellphone and 2-meter ham bands, and the modulation techniques also are very important — especially with the digital modulation technology used by many cellphone services.
Some digital modulation schemes need only 1/100th as much radiated power as analog systems, and still offer quite a bit of protection from co-channel interference (including multipath distortion).
Total posts : 45366Hi Rich,
Yes, I was comparing apples to oranges but just wanted to illustrate that 100 mW. or so is not such a low power under the right circumstances.
For those who are interested, I have read accounts of hams operating QRP (low power) on 160 meters (1.8 MHz.) with 100 or so mW. and with appropriate antennas (vertical masts if I recall, 60 feet or so) have been heard 180 miles away. They were using some sort of ultra low bandwidth digital modulation. I don’t remember the details but I recall the bandwidth was about 1/2 Hz.
Narrow bandwidth gives an advantage when the signal is extremely weak and is used by NASA for space probes. At NASA frequencies the noise is proportional to the square root of the bandwidth (among other things), so small bandwidth improves the S/N ratio. The signal from the Pioneer Probe used a bandwidth of 10 Hz. Morse code takes more than that.
Neil
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