Help: Ready to put a part 15 am on air, Now what to do next.

[JasonW]

Here are links to two pictures of a Honda "Talking Billboard," .... This is the standard InfoMAX (a.k.a. Talking House) weatherproof outdoor enclosure offered by Information Station Specialists, topped by the standard 8.5' Part 15 AM whip antenna (a CB whip).

The 8.5 foot whip in those photos is a "standard" Part 15 AM whip only if it, plus any other radiating source is 3 meters or less in length. But in these photos it is likely that the tx "ground" terminal is connected to the steel frame of the billboard. As the billboard frame is longer (higher) than the whip, it would radiate more r-f than the whip itself, and certainly mean that the radiating length in this system was greater than 3 meters.

This reality of physics either isn't being recognized, or it is being ignored by ISS (if they support it), "Part 15" operators, and, according to these boards -- even the FCC.
//

The alternative Part 15.219 AM rules (which, unlike the Part 15.209 AM rules, don't involve field strength at all) were written with the full knowledge that tens of thousands of these AM transmitters are used every day by lay people who are not broadcast engineers. Determining Part 15.209 compliance of every one of these Part 15 AM transmitter installations by measuring the field strength would be a logistical nightmare for both the FCC and the transmitter users.

The Part 15.219 limits (100 milliwatt input to the final RF stage, 3 meter antenna + antenna feed line [if any] + ground lead total length, emissions below 510 kHz or above 1705 kHz kept at least 20 dB below the level of the unmodulated carrier) were deliberately set this low so that unknown and unpredictable (to a lay user) factors that enhance the signal strength (even setting the transmitters on metal desks noticeably increases the range through capacitive coupling) will not increase it so much that it will cause interference to licensed stations. Also, the transmitter manufacturers include instructions for finding local open AM frequencies for both day-time and night-time use.

The FCC knows that these AM transmitters (which are mostly used by realtors to advertise houses and other buildings that are up for sale) will sometimes put out stronger-than-usual signals if their outdoor ATU/whip antenna units are mounted on metal buildings or on buildings whose structures contain metal parts such as studs. The very low output power and very small (in terms of wavelength) antenna size ensure that the transmitters won't cause interference even if they're mounted on objects that make good RF grounds. This makes it easier on the FCC (whose regional offices and field agents have far more important things to do) as well as the transmitter users.

-- Jason

 

[rfry]

The alternative Part 15.219 AM rules (which, unlike the Part 15.209 AM rules, don't involve field strength at all) were written with the full knowledge that tens of thousands of these AM transmitters are used every day by lay people who are not broadcast engineers. Determining Part 15.209 compliance of every one of these Part 15 AM transmitter installations by measuring the field strength would be a logistical nightmare for both the FCC and the transmitter users. (etc etc)

Your post includes beliefs and interpretations that many Part 15 AM users seem to depend upon, but certainly they are not based on the technical reality.

I guess we both have had our say on this now. I know the information I posted could cause grief to some readers. Thanks for the non-inflammatory tone of your replies.

Rich

//

 

[JasonW]

The alternative Part 15.219 AM rules (which, unlike the Part 15.209 AM rules, don't involve field strength at all) were written with the full knowledge that tens of thousands of these AM transmitters are used every day by lay people who are not broadcast engineers. Determining Part 15.209 compliance of every one of these Part 15 AM transmitter installations by measuring the field strength would be a logistical nightmare for both the FCC and the transmitter users. (etc etc)

Your post includes beliefs and interpretations that many Part 15 AM users seem to depend upon, but certainly they are not based on the technical reality.

I guess we both have had our say on this now. I know the information I posted could cause grief to some readers. Thanks for the non-inflammatory tone of your replies.

Rich

//

I deal with facts. The FCC does, however, interpret its own rules at times. FCC field agents are also free (within reasonable limits) to make on-site judgements concerning compliance. Depending on the situation, they sometimes go by "the spirit of the law" rather than "the letter of the law." (This is not unusual, because the FCC is a government agency that deals in law, which is often subject to interpretation.) It is a fact that these billboard transmitters have been inspected and found to be compliant by FCC field agents. I can give you two examples right here, one of which even includes the name of the field agent who -twice- inspected and passed the same billboard transmitter as compliant:

[EXAMPLE 1] In 1997-1998, a Part 15 AM billboard transmitter operating on 1570 kHz in Tustin, California (a "Trans-AM," FCC ID. Number DPD624TA100, manufactured by Ultra Sensors, Inc.) was reported to the FCC by local broadcast engineers. On a good car radio, the signal was barely readable at 1/2 mile and was clear within 100 - 200 yards of the billboard. On two occasions, Mr. Paul Oei of the FCC's Compliance and Information Bureau in Los Angeles inspected the billboard station, found that it was using an FCC Type-Accepted transmitter, and declared it legal under Part 15.219.

[EXAMPLE 2] In the Stockton, California area, a Part 15 AM billboard transmitter (see it here at www.netfeed.com/~jhill/1610.htm ) was broadcasting on 1610 kHz. Looking at the pictures, it was an InfoMAX (a.k.a. Talking House) unit with the transmitter in a weatherproof cabinet at the base of the billboard and the ATU/whip in a weatherproof enclosure up on the billboard. It could be heard 3 - 10 miles up and down the highway from the billboard. (While this is unusual, it is not unheard-of for well-designed Part 15 installations in areas with good ground conductivity.) It was reported to the FCC, who took field strength readings and were apparently satisfied that the installation was legal, because they took no further action.

When they formulated the Part 15.219 rules, the FCC was fully aware that the transmitters or their outdoor ATUs would be DC-grounded to all kinds of conductive objects and that some of them could act as effective counterpoises or even radiate as the other half of a de facto dipole. It is a "happy accident" that the metal billboards help to boost the signal strength, but FCC field agents don't get excited about these or other installations as long as (1) the transmitters are either FCC Type-Accepted or FCC-Certified and (2) there is no evidence of a blatant attempt to dramatically increase the signal strength (such as using a 1/4 wavelength counterpoise wire that is connected to nothing at its far end). In installations other than this, the very low power and very small antenna size keep the signal from causing interference even if the field strength does exceed the Part 15.209 limit. 0.1 watts can only go so far...

-- Jason

 

[rfry]

[EXAMPLE 1] In 1997-1998, a Part 15 AM billboard transmitter operating on 1570 kHz in Tustin, California (a "Trans-AM," FCC ID. Number DPD624TA100, manufactured by Ultra Sensors, Inc.) was reported to the FCC by local broadcast engineers. On a good car radio, the signal was barely readable at 1/2 mile and was clear within 100 - 200 yards of the billboard. On two occasions, Mr. Paul Oei of the FCC's Compliance and Information Bureau in Los Angeles inspected the billboard station, found that it was using an FCC Type-Accepted transmitter, and declared it legal under Part 15.219.

Two points here. (1) The distances you report are not greater than can be expected for a good 100 mW Part 15 AM tx with a resonant antenna system total radiating structure of 3 meters, or even less. (2) FCC acceptance/certification of the tx itself means nothing if it is being used with an antenna/ground lead+conductor having a radiating length greater than 3 meters.

[EXAMPLE 2] In the Stockton, California area, a Part 15 AM billboard transmitter (see it here at www.netfeed.com/~jhill/1610.htm ) was broadcasting on 1610 kHz. Looking at the pictures, it was an InfoMAX (a.k.a. Talking House) unit with the transmitter in a weatherproof cabinet at the base of the billboard and the ATU/whip in a weatherproof enclosure up on the billboard. It could be heard 3 - 10 miles up and down the highway from the billboard. (While this is unusual, it is not unheard-of for well-designed Part 15 installations in areas with good ground conductivity.) It was reported to the FCC, who took field strength readings and were apparently satisfied that the installation was legal, because they took no further action.

"Apparently" is a loaded descriptor. Please provide your proof that this is true. And was this coverage true for the typical home listener, or only for those with very sensitive receivers such as automotive receivers, with good antennas, and listening locations with no overhead wires, power line noise and/or other interference, and a vested interest in promoting such coverage claims and expectations for Part 15 AM systems?

When they formulated the Part 15.219 rules, the FCC was fully aware that the transmitters or their outdoor ATUs would be DC-grounded to all kinds of conductive objects and that some of them could act as effective counterpoises or even radiate as the other half of a de facto dipole.It is a "happy accident" that the metal billboards help to boost the signal strength, but FCC field agents don't get excited about these or other installations as long as (1) the transmitters are either FCC Type-Accepted or FCC-Certified and (2) there is no evidence of a blatant attempt to dramatically increase the signal strength (such as using a 1/4 wavelength counterpoise wire that is connected to nothing at its far end). etc

You write as if you are an absolute authority on the thought processes and intent of the FCC. But aren't your statements just subjective beliefs and concepts, and not the "facts" you have claimed to deal with in the first sentence of your last post?

The real facts for Part 15 AM as written in 15.219 say that (1) 100 mW is the maximum DC input power to the final r-f stage in the transmitter, and (2) the total length of the radiating structure cannot exceed 3 meters. Physics tells us that using a 3-meter radiator on top of a billboard, tower, flagpole, or rooftop with a long "ground lead + ground wire" exceeds that 3-meter radiating length. THOSE are the facts that Part 15 operators need to consider, if they want to comply with Part 15 as it is written.

As to your previous post about ISS installations, please note the response below that I received today from the ISS Product Manager when I asked for clarification about your posted statements. I did not identify you as the "poster."

Poster: Information Station Specialist's ACTIONS *fully* support my earlier
posts. They continue to install Part 15 AM transmitters on metal billboards
(Honda recently used the "talking billboards" in one of their ad campaigns),

ISS: We do not install the systems.

Poster: and ISS offers weather-resistant metal transmitter enclosures that
are bolted to the billboards to form good ground connections.

ISS: The chassis of the enclosure is not connected to the RF ground in any
way. Nor do we make provision for such.

Poster: Cadillac uses these "talking billboards" rather often in their
"Radio Cadillac" ad campaigns, and they've done so for at least ten years.

ISS: Not sure, but we don't think we've ever sold anything to the Cadillac
division.

Poster: If the FCC really cared about this, they would have long ago shut
down every "talking billboard" Part 15 AM station and raided Information
Station Specialists, just as they've raided Ramsey Electronics several times
for selling non-compliant Part 15 FM transmitters. /QUOTE

ISS: We have heard from a some of our clients that their systems were
inspected. They passed.
//

 

[JasonW]

R. Fry wrote:

<Two points here. (1) The distances you report are not greater than can be expected for a good 100 mW Part 15 AM tx with a resonant antenna system total radiating structure of 3 meters, or even less. (2) FCC acceptance/certification of the tx itself means nothing if it is being used with an antenna/ground lead+conductor having a radiating length greater than 3 meters.>

Agreed, on both points. Remember, though, that these billboard transmitters have been in use for many years and have a track record of not causing problems, provided that FCC Type-Accepted or FCC-Certified Part 15 AM transmitters are used in the installations. Like any government regulatory agency, the FCC often acts (or refrains from acting) on the basis of precedents.

<"Apparently" is a loaded descriptor. Please provide your proof that this is true.>

The web site itself is the proof. If the FCC had shut down the 1610 kHz billboard transmitter in the Stockton area, the site owner would have reported it.

<And was this coverage true for the typical home listener, or only for those with very sensitive receivers such as automotive receivers, with good antennas, and listening locations with no overhead wires, power line noise and/or other interference, and a vested interest in promoting such coverage claims and expectations for Part 15 AM systems?>

The site owner was a proponent of the then-proposed Low-Power FM (LPFM) service. As he indicated on the web site, he was listening to the billboard transmitter on a stock AM/FM car radio in a 1995 model Saturn car. It's possible that the signal was unintentionally conducted along power lines or telephone lines running beside the road, which could have given him the incorrect impression of a large omni-directional range. (My Talking House transmitter barely gets out two blocks due to the poor local soil conductivity, yet it achieves ranges of up to 1/2 mile when I lay the whip antenna on my living room floor, parallel to the power lines outside. This increased range *only* occurs under and next to the power lines.)

<You write as if you are an absolute authority on the thought processes and intent of the FCC. But aren't your statements just subjective beliefs and concepts, and not the "facts" you have claimed to deal with in the first sentence of your last post?>

The FCC is a federal law enforcement agency, albeit one with an unusual and highly specialized jurisdiction. Having relatives who are in law enforcement (including a cousin who is a federal magistrate) and having personally dealt with the FCC myself gives me insight into how they think.

Several years ago I spoke with the Anchorage FCC office regarding setting up community radio stations in a few remote arctic Inuit villages, using Talking House Part 15 AM transmitters with 1/4 wavelength Folded Marconi antennas and full-size radial systems to overcome the poor local soil conductivity. They said that they had no objections, since the 0.1 watt signals originating hundreds of miles away from the nearest other settlements couldn't possibly cause interference even by skywave propagation. They likened it to walking around nude outside at 3 AM. Although that would break the public nudity laws, no crime is committed if no one sees the "bodily display." That is also the FCC's attitude toward the billboard transmitters--"no harm (no interference), no foul."

Remember, the FCC's goal in this area is *not* to maintain certain field strength values, but to *prevent interference.* The various field strength limits, power output limits, and antenna size limits in the various frequency bands are only means to achieving that end (preventing interference), and the values were chosen to "err on the side of caution." But if there is no interference even when those limits are occasionally exceeded, there is (to them) no problem.

<ISS: We have heard from a some of our clients that their systems were inspected. They passed.>

I rest my case...


-- Jason

 

[rfry]

Remember, the FCC's goal in this area is *not* to maintain certain field strength values, but to *prevent interference.* The various field strength limits, power output limits, and antenna size limits in the various frequency bands are only means to achieving that end (preventing interference), and the values were chosen to "err on the side of caution." But if there is no interference even when those limits are occasionally exceeded, there is (to them) no problem.

Your statements again assume that you know what the FCC is thinking on this topic, and that it is different than the words in Part 15. If what you write is true, why doesn't Part 15 reflect that? The rules could say something like, "Any radiated power may be used as long as it causes no interference." But the rules do not permit that, and those operating and/or suggesting to others to operate as if they did are clearly at risk.

<ISS: We have heard from a some of our clients that their systems were inspected. They passed.> I rest my case...

Of course the configurations that were inspected were not stated. They could have been for the InfoMAX version with the short wire antenna, and not using an elevated, over-length antenna.

The ISS response to your statements shows that your other claims about them were incorrect.
//

 

[JasonW]

It doesn't matter who installs the billboard Part 15 AM transmitters, be it ISS or other firms. The long-term continued operation of billboard AM transmitters across the USA with no problems other than occasional FCC inspections refutes your assertions about their being illegal.

The FCC's word is the final word regarding the tranmitters' legality, and since they don't shut down these billboard transmitters their word obviously disagrees with yours. If you don't like it that's your problem, not theirs (or mine).

Now go run along and play with your antenna modeling software.


-- Jason

 

[rfry]

Very good. You've told people your opinion of how much you think they can exceed Part 15 FCC limits without getting gigged.

I've told people about the limits given by Part 15 according to the laws of physics.

So both limits have been given, and now people can make their own decisions about how they want to operate.

//

 

[SUPERCASTER]

Ground conductivity in a radially grounded monopole antenna plays a very important part in AM broadcast ground wave propagation, as opposed to higher frequency antennas used primarily to transmit sky waves.
If the current in 2 opposite legs of a ground radial system were oppositely phased by the presence of dirt and currents exactly cancelled there would be no effect on the RF signal and therefore no reason for the radials. Ground resistance, in effect, would be infinite, and the radials ineffective.
There is nothing in dirt that makes electrons or currents change phase or behave stangely as you claim. The earth (dirt) behaves as a conductor just as any other conductor such as copper.
The links to illustrations you created with your software don't seem to shed any light on the mysterious phase reversal effects you claim for dirt.

 

[rfry]

There is nothing in dirt that makes electrons or currents change phase or behave stangely as you claim. The earth (dirt) behaves as a conductor just as any other conductor such as copper. The links to illustrations you created with your software don't seem to shed any light on the mysterious phase reversal effects you claim for dirt.

But I haven't been writing about radials buried in dirt. Please re-read the thread. The antenna system I'm describing is mounted totally above the earth, for use on the upper floors of an apartment building (which is what started this whole thread). It doesn't USE a "ground connection" buried in the dirt, and it shouldn't HAVE one. It operates similar to a "ground plane" antenna such as more commonly used at VHF and above, but with much less efficiency.

I didn't write that the currents in the two halves of the elevated horizontal wire had reversed phase. That is your statement. What I wrote is that the net field radiated from the horizontal wire was ~ zero -- and it is, because even through the instantaneous r-f currents in the two halves of the horizontal wire are equal and in phase, they are flowing in opposite (compass) directions. THAT is why the net radiated field from the horizontal wire is zero.

The NEC-2 surface pattern plot that I linked to earlier in this thread verifies this fact. Note there that the complete antenna model including the horizontal wire are elevated above the flat "grid" structure in the graphic, which flat grid is the earth. As you can see, there is/are no metallic conductor/s between the antenna wires and the earth.

If this post doesn't clear up this subject for you, I suggest you consult a few antenna engineering textbooks for more detail.

//

 

[SUPERCASTER]

Implying ignorance and insulting others is not very useful and reflects poorly on someone, such as youself, claiming to be a professional. Doctors, lawyers, engineers, scientists and others often disagee, but can have a discussion without becoming disageeable. If you are a professional, as you claim, you should start behaving as one.

 

[rfry]

Implying ignorance and insulting others is not very useful ...

Sorry you took it that way. My original posts are made in a low-key, informational manner, and only get more direct as necessary to get their original content understood.

Normally I would use a private message for such followups, but AFAIK, the Radio-Info board provides no means for this.

If you send me your email address, maybe we can do this in the future. Mine is rfry at adams.net

//

 

[SUPERCASTER]

Implying ignorance and insulting others is not very useful ...

Sorry you took it that way. My original posts are made in a low-key, informational manner, and only get more direct as necessary to get their original content understood.

Normally I would use a private message for such followups, but AFAIK, the Radio-Info board provides no means for this.

If you send me your email address, maybe we can do this in the future. Mine is rfry at adams.net

//

Thanks for your message. Perhaps I misinterpreted the tone of your post.