Part 15 AM Coverage Capability: Reality Check

[Black_Shire]

Yes, some of the Part 15 FM modulators on the new HD radio receivers (intended to re-transmit the received signal to an existing analog FM car radio) have ranges up to 1/4 mile, which is *far* greater than the range of a Part 15 compliant FM transmitter!

However, the Talking House, TalkingSign, and AM1000 Rangemaster Part 15 AM transmitters have been around for many years and are in widespread use. If they were "out of spec" with regard to the Part 15 AM rules, their manufacturers would have long ago been cited by the FCC. (Ramsey has been raided by the FCC at least once, although the raid(s) was/were in connection with their non-compliant Part 15 FM transmitters rather than their Part 15 AM transmitters.)


-- Black Shire

One thing to keep in mind here is that the interpretation of the part 15 rules is up to the individual field inspector. The violation referenced in the earlier post was regarding an installation with *100'* of ground-lead wire. I'm sure it was apparent to the inspector that this installation was purposefully in violation of the rules. Who's to say if the same inspector would've scrutinized a residential rooftop installation with a 15' lead directly to ground? According to the Hamilton site, such installations have indeed passed an inspection and remained in operation without changes.

Do FCC rules trump the NEC? That really isnt a valid question, considering that it would still be possible to follow code by relocating the transmitter to ground level, or say, using a 1m ground lead, and a 2m antenna. Following the rules of these two regulating bodies is an "and" situation rather than an "or". Both should be taken into consideration for a given installation.

Just because a device is part 15 accepted (i.e. "real-estate" transmitters) doesn't necessarily mean that it is operating within the limits. Read the article in BERadio regarding "part 15" devices on the FM band... Most of them radiate way more than they are "supposed" to. Guess the FCC certification office needs to tighten the slack a bit. NPR is reeling over this, since most part 15 FM transmitters are in the NCE part of the band.

Part 15 transmitters cannot defy the laws of physics. Period. Certainly it can be difficult to calculate the real-world performance of these installations due the the infinite number of variables involved. I was thinkking of this thread earlier this week as I was using an HP signal generator to tune an ATU for an AM facility that I was moving. The generator put *out* 25mW, and the calculated efficiency of the feedline/ATU/ground system/soil conductivity/.225-wave tower was about 76%. This is still more than 10dB higer than a 'ground mounted' part 15. Modulated with 1000Hz tone, I took a drive and set the GPS on the dash. Signal was clear/listenable to about 1km, noisy/somewhat listenable by 2-2.5km, and by 3-3.5km was just barely perceptible or non-existent. I was able to go out to 4km in three directions, and even with the car off was unable to detect the presence of any signal.

 

[rfry]

I was thinkking of this thread earlier this week as I was using an HP signal generator to tune an ATU for an AM facility that I was moving. The generator put *out* 25mW, and the calculated efficiency of the feedline/ATU/ground system/soil conductivity/.225-wave tower was about 76%. This is still more than 10dB higer than a 'ground mounted' part 15. Modulated with 1000Hz tone, I took a drive and set the GPS on the dash. Signal was clear/listenable to about 1km, noisy/somewhat listenable by 2-2.5km, and by 3-3.5km was just barely perceptible or non-existent. I was able to go out to 4km in three directions, and even with the car off was unable to detect the presence of any signal.

The bold face attribute in some of the text in the quote above was my doing. But that original text is an important and contemporary, real-world statement from an unsolicited 3rd party, which supports the conclusions of earlier posts here about the real-world coverage capability of a legal Part 15 AM installation, and the physics on which they were based. And it supports the real-world field strength measurements made in the 1937 seminal study by Brown, Lewis & Epstein of RCA labs -- which to this day are the basis for FCC policy on these matters.

The bottom line? Part 15 AM tx/antenna systems that are truly compliant with the radiation physics defined by Part 15.219 cannot produce consistently useful groundwave field strength beyond a radius of a several thousand feet (best case), such as are needed by the average, cheap, indoor AM receiver and listener. And certainly not for a radius of 3-4 miles, unless the "Part 15" AM installation is non-complaint with Part 15.
//

 

[desert_er]

I have no doubt that the transmitters themselves are compliant, but a legal part-15 facility also requires a legal installation. the legal status of any installation is up to the individual field inspector.

It also needs to be kept in mind that when transmitters like the rangemaster were sent in for certification, it's doubtful (and would serve no purpose) that there was a ground rod and 35' of ground-lead cable included with the package.

Precedent has already been set on the use of an electrically connected ground lead. If you want your transmitter up high, you can't ground it.

 

[Black_Shire]

You just demonstrated your total lack of experience with Part 15 AM operations when you made reference to groundwave field stength.

Due to the tiny size (in terms of wavelength) of the 3 meter antenna, Part 15 AM operators intent on achieving maximum range use the highest open AM frequencies (1500 kHz or higher) available in their localities because the antenna is much more efficient at the higher frequencies.

Because groundwave propagation is much less effective at the higher AM frequencies, Part 15 AM operators rely on line-of-sight propagation to achieve maximum range. The higher AM frequencies also tend to be less plagued by atmospheric noise and man-made noise, which helps.


-- Black Shire

I was thinkking of this thread earlier this week as I was using an HP signal generator to tune an ATU for an AM facility that I was moving. The generator put *out* 25mW, and the calculated efficiency of the feedline/ATU/ground system/soil conductivity/.225-wave tower was about 76%. This is still more than 10dB higer than a 'ground mounted' part 15. Modulated with 1000Hz tone, I took a drive and set the GPS on the dash. Signal was clear/listenable to about 1km, noisy/somewhat listenable by 2-2.5km, and by 3-3.5km was just barely perceptible or non-existent. I was able to go out to 4km in three directions, and even with the car off was unable to detect the presence of any signal.

The bold face attribute in some of the text in the quote above was my doing. But that original text is an important and contemporary, real-world statement from an unsolicited 3rd party, which supports the conclusions of earlier posts here about the real-world coverage capability of a legal Part 15 AM installation, and the physics on which they were based. And it supports the real-world field strength measurements made in the 1937 seminal study by Brown, Lewis & Epstein of RCA labs -- which to this day are the basis for FCC policy on these matters.

The bottom line? Part 15 AM tx/antenna systems that are truly compliant with the radiation physics defined by Part 15.219 cannot produce consistently useful groundwave field strength beyond a radius of a several thousand feet (best case), such as are needed by the average, cheap, indoor AM receiver and listener. And certainly not for a radius of 3-4 miles, unless the "Part 15" AM installation is non-complaint with Part 15.
//

 

[rfry]

You just demonstrated your total lack of experience with Part 15 AM operations when you made reference to groundwave field stength.

The radiation and propagation of radio waves are governed by natural laws that apply no matter what the application is.

Due to the tiny size (in terms of wavelength) of the 3 meter antenna, Part 15 AM operators intent on achieving maximum range use the highest open AM frequencies (1500 kHz or higher) available in their localities because the antenna is much more efficient at the higher frequencies.

Nothing I have posted has stated otherwise. Note that the antenna system efficiency of 1% that I used in my opening post in this thread can only be achieved by a compliant, ground-mounted Part 15 antenna system at the extreme high end of the AM broadcast band (if then).

Because groundwave propagation is much less effective at the higher AM frequencies, Part 15 AM operators rely on line-of-sight propagation to
achieve maximum range.

The maximum field strength radiated by any vertical monopole always lies in the horizontal plane, no matter how short that monopole is in terms of wavelengths, or what the carrier frequency. Paper 3 at the web page linked below illustrates the physics of the elevated 3-m Part 15 AM system.

You are attributing the better performance of the elevated Part 15 antenna to line-of-sight propagation. But as shown in that paper, it is the result of radiation from wires attached to the Part 15 tx below the 3-m section -- which radiate more r-f than the 3-m section considered to be the complete antenna.

Such an antenna system has a functional length significantly greater than the 3-m length defined in 15.219. That, and not line-of-sight propagation is why such systems "work better."

http://rfry.org/Software & Misc Papers.htm

//

 

[Black_Shire]

*Of course* the radiation from the AC power lead and audio input lead helps in elevated Part 15 AM installations.

The point is that these AC power and audio input leads *are* allowed by the rules, while dedicated single-purpose ground wires are not.


-- Black Shire

You just demonstrated your total lack of experience with Part 15 AM operations when you made reference to groundwave field stength.

The radiation and propagation of radio waves are governed by natural laws that apply no matter what the application is.

Due to the tiny size (in terms of wavelength) of the 3 meter antenna, Part 15 AM operators intent on achieving maximum range use the highest open AM frequencies (1500 kHz or higher) available in their localities because the antenna is much more efficient at the higher frequencies.

Nothing I have posted has stated otherwise. Note that the antenna system efficiency of 1% that I used in my opening post in this thread can only be achieved by a compliant, ground-mounted Part 15 antenna system at the extreme high end of the AM broadcast band (if then).

Because groundwave propagation is much less effective at the higher AM frequencies, Part 15 AM operators rely on line-of-sight propagation to
achieve maximum range.

The maximum field strength radiated by any vertical monopole always lies in the horizontal plane, no matter how short that monopole is in terms of wavelengths, or what the carrier frequency. Paper 3 at the web page linked below illustrates the physics of the elevated 3-m Part 15 AM system.

You are attributing the better performance of the elevated Part 15 antenna to line-of-sight propagation. But as shown in that paper, it is the result of radiation from wires attached to the Part 15 tx below the 3-m section -- which radiate more r-f than the 3-m section considered to be the complete antenna.

Such an antenna system has a functional length significantly greater than the 3-m length defined in 15.219. That, and not line-of-sight propagation is why such systems "work better."

http://rfry.org/Software & Misc Papers.htm

//

 

[rfry]

*Of course* the radiation from the AC power lead and audio input lead helps in
elevated Part 15 AM installations. The point is that these AC power and audio input leads *are* allowed by the rules, while dedicated single-purpose ground wires are not.

Part 15.219 limits the radiating length/height of Part 15 AM antenna systems to three meters. Period.

Using one or more radiating conductors which functionally increase that permissible 3-m radiating length is non-compliant with 15.219, whether or not those conductors serve an additional purpose such as conveying audio or power or a "lightning ground" to an elevated Part 15 AM transmitter/antenna system.

People looking for loopholes might be glad to accept your beliefs. But physics proves otherwise, and could result in consequences for them with the FCC.
//

 

[Neil E.]

*Of course* the radiation from the AC power lead and audio input lead helps in elevated Part 15 AM installations.

The point is that these AC power and audio input leads *are* allowed by the rules, while dedicated single-purpose ground wires are not.

Maybe not. The rules do not mention these leads and to say that they are allowed is conjecture just as is my interpretation that they need to be included in the length limits.

If you consider my previous comments regarding the effect of these lines and the intent of the rules I trust you will agree that they have to be included in the tally of the total length of the antenna, transmission line, and ground lead since they contribute to radiation. Just labelling a wire a "dedicated" ground does no more to change its function than painting it purple.

With this in mind, it is probably unlikely that an inspector will get perturbed about the power line and audio cables but I think if they did they would have a techinical basis.

Neil

 

[Neil E.]

Addendum to my previous post.

With this in mind, it is probably unlikely that an inspector will get perturbed about the power line and audio cables for a desktop installation but I think if they did they would have a techinical basis. The situation is different with "elevated" transmitters since the length of the power and audio lines cannot just be considered a "little more" wire.

Neil

 

[Black_Shire]

If that were true, FCC Certified Part 15 AM transmitters such as the Talking House, TalkingSign, and AM1000 Rangemaster would not be sold with AC adapters that have 6 foot power leads, nor would the Talking House and TalkingSign be sold with microphones that also have 6 foot leads, for a total of 12 feet of conductors per transmitter *besides* the 3 meter wire antenna.

The AM1000 Rangemaster uses a 600 ohm balanced audio line that is specified in the instructions simply as being as long as is necessary to reach the transmitter.

The manufacturers of these three FCC Certified Part 15 AM transmitters must either have ALL bribed the FCC official in charge of Part 15 compliance to "look the other way," OR they must have compromising pictures of that same FCC official walking out of a hotel naked with a billy goat, OR...all three transmitters comply with Part 15.219 *with* their 6 foot power leads and 6 foot microphone leads.

In short, the FCC has either been fooled or defrauded into certifying *THREE* different illegal Part 15 AM transmitters (*SIX*, counting the two earlier versions of the Talking House and LPB's AM-2000 transmitter, all of which also have 6 foot or longer power leads [18 feet in the AM-2000's case] and microphones with 6 foot or longer leads [18 feet in the AM-2000's case]), OR...all six transmitters are compliant with Part 15.219.

Accepting the former supposition (that the FCC was fooled or defrauded *six times* into certifying illegal Part 15 AM transmitters) requires a level of belief that borders on total gullibility. The only remaining possibility is that all six of these Part 15 AM transmitters received their FCC Certifications because they do, in fact, comply with Part 15.219--power leads, audio leads, and all. You can believe whatever you want, but these transmitters (*with* their power and audio leads) are all Part 15 compliant and legal whether you like it or not.


-- Black Shire

*Of course* the radiation from the AC power lead and audio input lead helps in
elevated Part 15 AM installations. The point is that these AC power and audio input leads *are* allowed by the rules, while dedicated single-purpose ground wires are not.

Part 15.219 limits the radiating length/height of Part 15 AM antenna systems to three meters. Period.

Using one or more radiating conductors which functionally increase that permissible 3-m radiating length is non-compliant with 15.219, whether or not those conductors serve an additional purpose such as conveying audio or power or a "lightning ground" to an elevated Part 15 AM transmitter/antenna system.

People looking for loopholes might be glad to accept your beliefs. But physics proves otherwise, and could result in consequences for them with the FCC.
//

 

[Black_Shire]

The radiation from the transmitters' power cords and audio leads is so weak that I suspect they have RF chokes to block most of the signal that would otherwise flow into them, which could explain why these leads aren't mentioned in the rules.

I know the designer of the TalkingSign Part 15 AM transmitter, and I'll ask him about this.


-- Black Shire

*Of course* the radiation from the AC power lead and audio input lead helps in elevated Part 15 AM installations.

The point is that these AC power and audio input leads *are* allowed by the rules, while dedicated single-purpose ground wires are not.

Maybe not. The rules do not mention these leads and to say that they are allowed is conjecture just as is my interpretation that they need to be included in the length limits.

If you consider my previous comments regarding the effect of these lines and the intent of the rules I trust you will agree that they have to be included in the tally of the total length of the antenna, transmission line, and ground lead since they contribute to radiation. Just labelling a wire a "dedicated" ground does no more to change its function than painting it purple.

With this in mind, it is probably unlikely that an inspector will get perturbed about the power line and audio cables but I think if they did they would have a techinical basis.

Neil

 

[Neil E.]

Black Shire,

This is just speculation on my part but maybe these certified transmitters were certified under part 15.209 where the lengths and power are not specified.

Another thing you might be interested in is to search the FCC database by using the FCC ID number on these units. I have done this on some of my wireless thermometers and the report to the FCC and, even in some cases, the schematics were posted.

Link here:

https://gullfoss2.fcc.gov/prod/oet/cf/eas/reports/GenericSearch.cfm

I did this for the AM1000 but the information is apparently not available or is held as confidential.

If you talk to the TalkingSign designer, please let us know what you find. I think that will be interesting to all of us.

Neil

 

[carlvenorden]

Check out the sstran. www.sstran.com.
I build the antenna for it, and it is such an excellent tx system I'm surprised it wasn't mentioned!
With semi-good conductivity, and a clear channel at the high end of the band, a 2 mile signal is not unexpected. More is very possible too.

I understand the technical aspects of what is being said, but a legally installed part 15am will do a pretty good job in a fair field...........and you are really operating with a lot less than 1/10th of a watt.
Pretty darn good for the noicy world of AM today.

 

[Tom Wells]

I again suggest the viability of an expanded tank circuit, where L and/or C are physically large.

As is it not adressed as a possibility in the rules, it may offer a legal use of something larger than the 3m.

I am considering a horizontal plate capacity hat, with L vetically to attic.

 

[desert_er]

Given that the price is so attractive, I'd like to pick up one of the SSTRAN units to play with. I've seen that there is a modification posted on the website to match it into a base-loaded antenna; I wonder what the component values would be to get a 50-ohm output (or what the "stock" impedance is)? It'd be interesting to try some different matching network / antenna combinations to see what gave the best performance.

Too bad the rangemaster has the matching network built in... the carrier-sync capability of that unit would allow a phased array with multiple transmitters if you had the real-estate available.

I hope I didn't come off an an opponent to part 15 experimentation in my previous posts. On the contrary, I think it's quite unfortunate that the rules for milli-power broadcasting are as stringent as they are. I do, however, think that it is important to follow the law of the land, and hope that fellow experimenters keep in mind that their 'interpretation' of the FCC rules will always be trumped by the 'interpretation' of the field inspector, should a given installation garner the attention of the authorities (which is more likely if you start 'competing' with licensed broadcasters). It will be interesting to see if precedent ever gets set on *buried* ground radials. Unless you're on the seashore, ground losses are going to be nearly as much a limiting factor as the electrically short radiating element. The radials don't radiate per-se, but your effieciency could increase drastically. A circuit similar to the "MFJ artificial ground" might also be something fun to experiment with.

It's become quite popular on the Engineering board to post audio clips from various FM processing combinations. I'd be interested to hear a recorded clip of the received audio of a legal part 15 AM at given distances past, say, 2 or 3 km, with some details on the installation.

 

[rfry]

Unless you're on the seashore, ground losses are going to be nearly as much a limiting factor as the electrically short radiating element. The radials don't radiate per-se, but your effieciency could increase drastically.

To elaborate, a good r-f ground is possible even in soils with poor conductivity by using the classic "broadcast" system of 120 buried radials each at least 1/4-wave long. The r-f resistance of such a radial system generally is two ohms or less, compared to an r-f resistance of 20 ohms or more for an 8' ground rod (or even several connected together), a "water pipe" ground and similar.

The ground conductors need to be physically located where they can most efficiently collect the r-f currents induced in the earth by antenna radiation, and return them to the system with minimum loss. Those currents enter the earth out to a least 1/4 wavelength from the vertical radiator.

The radiation efficiency of a MW monopole vertical antenna is the ratio of its radiation resistance to the sum of all r-f resistances in the antenna system. The ground system resistance is the biggest of those by far in a typical Part 15 setup. Even at 1700 kHz the radiation resistance of a 3-m radiator is barely 1/10 of an ohm, so it is clear why the r-f resistance of the ground system should be minimized (with consideration for r-f bandwidth).

A very good r-f ground means that the signal is being "launched" from the antenna system with nearly the highest possible efficiency (other things equal). Once launched it will be subject to propagation losses, and for a given antenna site nothing much can be done to reduce those.

//

 

[Black_Shire]

Gerry Herlinger, the designer of the TalkingSign www.talkingsign.com Part 15 AM transmitter, kindly answered my query about AC power & audio input leads on Part 15 AM transmitters as regards their FCC certification. Here is his reply:


First, let's contemplate the original intentions of the the FCC ruling:

They wanted to allow AM transmitters which could never compete or interfere with any commercial broadcast - that's
why they only allowed 100mW of power and ridiculously short antennas for the frequencies involved. The antenna, transmission line and ground was devised to make sure that it was kept that way and even if some lattitude was allowed in this area, the final outcome for performance was still guaranteed to be poor. Proof: during my development, I set the transmitter to the same as a commercial station. The range of my transmitter was 1 metre!!

People don't seem to understand the AGC characteristics of AM receivers. If a channel is completely clear, the receiver will increase its gain rather like our hearing when it's quiet. Thus the phrase "you can hear a pin drop." If a low power transmitter is turned on, then yes, you will get good range. At this point, people start complaining that something must be wrong or illegal with the transmitter and start looking for illegalities in the set up.

The argument of parasitic help from AC adapter cords and audio leads is no different from assistance from nearby electric power lines, fences etc. We all know you don't have to be physically connected for benefits. BUT, these transmitters are so feeble, that for commercial purposes, thay almost don't cut it!

That's why this issue becomes a legal/political animal and that if you follow the FCC rules: antenna + transmission line + ground = 3m, then all is OK. You are correct: the legalities make no mention of audio leads, AC adapter leads etc.

If you read about the FCC allowance on Hamiltons site re: grounding, you can see that the FCC agents do seem to allow "longer grounds" for safety reasons. I bet this is in part due to their concern that a lawsuit could result if an ungrounded of poorly grounded outside transmitter was struck by lightning and entered into a home and hurt or
killed somebody - after all, the US is famous for lawsuits. If these guys stuck to their rules to the letter, then surely this would never be allowed, but it is.

In answer to your question: yes I have an RF choke in line with the power - but it does not stop the signal very much. I did have to use a grounded AC adapter of the switching type because it had a common mode filter to prevent switching frequencies from being conducted onto the line. For class B conducted emissions, they look at frequencies from 450kHz to 30MHz and these have to be within certain limits. You cannot use a regular AC transformer type wall adapter with these transmitters if they are close to the transmitter like the TalkingSign. I can only assume that Hamilton's transmitter was tested with the transmitter far away from the wall adapter - that's why he can use a cheapo type adapter. BTW, the Talking House wall adapter is an AC transmformer type with special filtering added in for the same reason.

No, I don't have any filtering on the audio jacks - it never came up in the labs tests because it is not a required part of the tests.

Cheers,
Gerry


-- Black Shire

Black Shire,

This is just speculation on my part but maybe these certified transmitters were certified under part 15.209 where the lengths and power are not specified.

Another thing you might be interested in is to search the FCC database by using the FCC ID number on these units. I have done this on some of my wireless thermometers and the report to the FCC and, even in some cases, the schematics were posted.

Link here:

https://gullfoss2.fcc.gov/prod/oet/cf/eas/reports/GenericSearch.cfm

I did this for the AM1000 but the information is apparently not available or is held as confidential.

If you talk to the TalkingSign designer, please let us know what you find. I think that will be interesting to all of us.

Neil

 

[Black_Shire]

I again suggest the viability of an expanded tank circuit, where L and/or C are physically large.

As is it not adressed as a possibility in the rules, it may offer a legal use of something larger than the 3m.

I am considering a horizontal plate capacity hat, with L vetically to attic.

I don't know if your typical FCC field agent would go along with that, *but* it would be perfectly legal under Part 15.209 ( www.part-15.org/fcc/part15/15-209.htm ), which goes by field strength unlike Part 15.219. As long as it didn't exceed the field strength limit, it would be FCC-kosher. Here are the Part 15.209 rules:


CATEGORIES


Subpart C -- Intentional Radiators - §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:


------------------------------------------------------------------------
Measurement
Frequency (MHz) Field strength distance
(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 3
------------------------------------------------------------------------
** Except as provided in paragraph (g), fundamental emissions from
intentional radiators operating under this section shall not be
located in the frequency bands 54-72 MHz, 76-88 MHz, 174-216 MHz or
470-806 MHz. However, operation within these frequency bands is
permItted under other sections of this part, e.g., §§ 15.231
and 15.241.


(b) In the emission table above, the tighter limit applies at the band edges.

(c) The level of any unwanted emissions from an intentional radiator operating under these general provisions shall not exceed the level of the fundamental emission. For intentional radiators which operate under the provisions of other sections within this part and which are required to reduce their unwanted emissions to the limits specified in this table, the limits in this table are based on the frequency of the unwanted emission and not the fundamental frequency. However, the level of any unwanted emissions shall not exceed the level of the fundamental frequency.

(d) The emission limits shown in the above table are based on measurements employing a CISPR quasi-peak detector except for the frequency bands 9-90 kHz, 110-490 kHz and above 1000 MHz. Radiated emission limits in these three bands are based on measurements employing an average detector.

(e) The provisions in §§15.31, 15.33, and 15.35 for measuring emissions at distances other than the distances specified in the above table, determining the frequency range over which radiated emissions are to be measured, and limiting peak emissions apply to all devices operated under this part.

(f) In accordance with §15.33(a), in some cases the emissions from an intentional radiator must be measured to beyond the tenth harmonic of the highest fundamental frequency designed to be emitted by the intentional radiator because of the incorporation of a digital device. If measurements above the tenth harmonic are so required, the radiated emissions above the tenth harmonic shall comply with the general radiated emission limits applicable to the incorporated digital device, as shown in §15.109 and as based on the frequency of the emission being measured, or, except for emissions contained in the restricted frequency bands shown in §15.205, the limit on spurious emissions specified for the intentional radiator, whichever is the higher limit. Emissions which must be measured above the tenth harmonic of the highest fundamental frequency designed to be emitted by the intentional radiator and which fall within the restricted bands shall comply with the general radiated emission limits in §15.109 that are applicable to the incorporated digital device.

(g) Perimeter protection systems may operate in the 54-72 MHz and 76-88 MHz bands under the provisions of this section. The use of such perimeter protection systems is limited to industrial, business and commercial applications.

[54 FR 17714, Apr. 25, 1989; 54 FR 32339, Aug. 7, 1989; 55 FR 18340, May 2, 1990; 62 FR 58658, Oct. 30, 1997]





Authority: 47 U.S.C. 154, 302, 303, 304, 307, 336, and 544A.


Source: 54 FR 17714, Apr. 25, 1989, unless otherwise noted.


-- Black Shire