Setting new precedent for outdoor Part 15, From Keith Hamilton

[rfry]

In the past, the FCC recognized new and pre-existing construction. Under this interpretation of the rules, they would not have considered the water tower as part of the ground. But, they would count a new tower that one built specifically to broadcast.

This belief has been posted before, but as far as physics and practical experience are concerned -- there is little to no difference in the radiation possible from a pre-existing metallic structure such as a water tower, flagpole, or billboard/building frame believed to be a Part 15 AM "ground," and a new one of equal dimensions.

All such structures so used can radiate, and may result in an unlicensed system that is functionally non-compliant with 15.219(b).

Just to repeat again that people are free to install and operate whatever they wish, at whatever FCC risk they wish to accept. The only goal/agenda in this post is to offer some provable, technical points to assist in such decisions.

RF

 

[Flying-Dutchman]

Hi Rich,
I have never been a part 15er. I owned full power FM commercial
stations.
The man who provided the above info, posted by me was the
Engineer In Charge of the FCC Field Office in Chicago. He is the
one who said he did not count pre-existing construction. I must
add though, he has been retired for 20 years now and is no
longer able to cut anyone a break.
I thought his interpretation was fair. But, this interpretation
now appears to be history.
And, I don't think any of my businesses would have been threatened by some guy with a part 15 device.
Low Power AM might bring a little excitement back to the dying
AM broadcast band.

 

[Hamilton]

I said the AM1000FIL was found to be effective, because this was the first finding by agent Nguyen, he later reconsidered that finding.

I don’t see this as any “disaster” for part 15 at all, all the FCC said is the they did not find the filter used, in that configuration, (Ken C) “effective”.

Not a big deal….


I am working on a new more effective design for the AM1000FIL.

I agree about Part 15 not being a threat to full power broadcasters, I can’t see how a transmitter that can run all day off a 9 volt transistor radio battery could be considered a threat to a full powered FCC licensed station.

 

[edarmsttrong]

I agree about Part 15 not being a threat to full power broadcasters, I can’t see how a transmitter that can run all day off a 9 volt transistor radio battery could be considered a threat to a full powered FCC licensed station.

Ask the NAB lobbyists about this one...

It's simple. If the FCC doesn't want you on the air, your not on the air.At any power level.
Welcome to the land of the free and the home of the brave!

 

[druidhillsradio]

Low Power AM might bring a little excitement back to the dying
AM broadcast band.

Well said.

 

[Ermi Roos]

As I recall earlier on-line discussions about this subject, it was said that the FCC tests at Ken Cartwright's transmitter site were intended to compare the field strength with the ground lead disconnected to the field strength with the ground lead and Hamilton's filter in place. The logic was that if the system with the filter does not produce much more field strength than with the ground lead disconnected,the filter is proved to be effective.

The recent letter Ken Cartwright received from the FCC does not say anything about the field strength with the ground lead disconnected. Instead, comparisons were made with the ground lead installed with the filter and without the filter. Apparently, the OET, which evaluated the test data taken by the agent, did not think that the filter attenuated enough to negate the antenna gain increase resulting from mounting the transmitter on a 40-foot tower. Perhaps the OET Laboratory staff also realized that the so-called "ground lead," which is connected to the transmitter case, is not the only path to ground from the transmitter. There are also RF paths to ground from the audio and power cables.

It's too bad that the OET did not publish a technical report with field strenght measurements to explain their decision in detail. Without a report, the best we can do is read between the lines.

 

[Flying-Dutchman]

Every time we have a new president in the White House, we find a
change at the FCC. There is a new interpretation of the rules. I
think under this current administration we may be able to get more
sympathy for low power radio.

Let's face it. When the FCC type certified the Rangemaster, they
knew darn well that nontechnical people were going to buy it and
use it to run low power radio stations.

The rule that the Rangemaster was certified under is exempt from
field strength measurements. And, people are being cited who had
every intention of being legal.

It is time to get a new opinion on this matter from the FCC in
Washington. Someone being cited for mounting a Rangemaster
to a pre-existing structure is just ridiculous. It's a part 15 device.

 

[Jay Peninger]

Any organization which has to create and enforce policy including our FCC generally try to leave a fair amount of gray area because it allows them to cast a larger net when they go fishing for violations and they know for the most part the average person isn't going to challenge their authority.

 

[Flying-Dutchman]

Anyone remember those plans and kits for little part 15 AM transmitters
back in the 1970's. The instructions told you to ground to a cold water
pipe in your home.

OK. You measured the ground wire to the water pipe. You were
not expected to know the length of the water pipe above ground
because the pipe did not count. It was pre-existing construction.

 

[radioman148]

Anyone remember those plans and kits for little part 15 AM transmitters
back in the 1970's. The instructions told you to ground to a cold water
pipe in your home.

OK. You measured the ground wire to the water pipe. You were
not expected to know the length of the water pipe above ground
because the pipe did not count. It was pre-existing construction.

Hell, I ran a part 15 in the early 60s. I ran about 250 ft of bell wire wrapped around my house that I bought at the hardware store. The transmitter was a knight kit from Allied radio. I used a 4 channel mono mixer--2 turntables & a webcor reel tape recorder. Never worried about a ground wire. Got out about a half mile and had alot of fun. I was 12--14 years old.

 

[rfry]

...Apparently, the OET, which evaluated the test data taken by the agent, did not think that the filter attenuated enough to negate the antenna gain increase resulting from mounting the transmitter on a 40-foot tower. Perhaps the OET Laboratory staff also realized that the so-called "ground lead," which is connected to the transmitter case, is not the only path to ground from the transmitter. There are also RF paths to ground from the audio and power cables.

However an unlicensed, elevated Part 15 AM transmitter needs no path to ground in order to have a functional radiating structure greater than the 3 meter length permitted by Section 15.219(b). All it needs is a minimum of one conductor (other than the 3-meter whip) to produce higher field strengths than a typical earth-mounted configuration.

Any conductor(s) whether used for DC power, program, or "ground" that are attached to the r-f ground terminal or chassis of the elevated transmitter become one arm of a dipole antenna together with the 3-m whip -- even though such conductors connect to nothing at all at their opposite end(s) !

The link below leads to a NEC analysis of this, showing that an elevated vertical dipole 13 meters long whose lower arm tip is located 3 meters above a perfect earth, and is series fed 3 meters below the top has a gain that is ~18 decibels greater than a typical, ground mounted monopole (other things equal) -- even though that elevated system has no connection to an earth ground, whatsoever.

That ~18 dB gain is the equivalent of using a transmitter with ~63 times more power than the typical power possible from an earth-mounted system that is functionally compliant with 15.219.

http://i62.photobucket.com/albums/h85/rfry-100/OCF_Dipole_No_Ground.gif

RF

 

[Hamilton]

Rich,
That is just not a practical , statement, in our unit none of the control signals connect directly to the RF ground.
You should be confirming theory speculation with hard field experimentation.

 

[rfry]

Rich,that is just not a practical , statement, in our unit none of the control signals connect directly to the RF ground.

Even when/if true, whatever single conductor or conductors in series as are connected to the transmitter r-f ground terminal does/do not need to be connected to an r-f ground at the opposite end, in order for that conducting path to add to the radiation efficiency of the antenna system.

In fact, the opposite end of the conductor attached to the tx r-f ground terminal in the NEC model I linked to is not physically connected to anything, yet that antenna configuration has much higher gain than an earth-mounted monopole that functionally meets 15.219(b).

RF

 

[Flying-Dutchman]

The rule that the Rangemaster was type certified under says absolutely
nothing about the length of audio wires or power supply leads. And, field strength is irrelevant. This rule has enabled boy scouts, teachers, kids, and the handicapped to tinker. The rule was really designed for nontechnical people.

These people are not hurting us. We do not need further restrictions
on part 15.

The truth is this. My next door neighbor could put a low power AM
on and I would not even know it unless he told me. Why? I haven't
heard any good programing there in years. So, I no longer use the
AM band.

Maybe, if someone put something interesting on AM some of us would
have a reason to tune in. If not, AM will soon be dead.

 

[Ermi Roos]

R. Fry is correct that the far end of what we call the "ground lead" does not have to be connected to ground, or to anything else, in order to radiate. Even without an NEC simulation, it is pretty obvious that this is true. The 3 meter "antenna" and the ground lead form a vertical off-center dipole. Both sides of the dipole will radiate whether the connection to ground is present or not. The dipole radiation is appreciably higher, however, when the ground lead is connected to ground than when it is not.

 

[rfry]

R. Fry is correct that the far end of what we call the "ground lead" does not have to be connected to ground, or to anything else, in order to radiate. ...

Many posts define the "ground lead" as only the short conductor connecting the r-f ground terminal or chassis of a transmitter to another conductor assumed to be "ground."

But a functional r-f ground does not exist at the top of the long, vertical conductor that the short "ground lead" of an elevated Part 15 AM transmitter typically connects to -- even though that long conductor is connected to a functional, r-f earth ground at the bottom using ground rods, a water pipe, or buried radials.

The resistive path from the top of that long wire to earth potential may be near zero ohms for the flow of direct current, but it is much greater than zero ohms for radio frequencies. The reason for that is related to the fact that this long conductor is radiating those radio frequencies.

This means that the long wire together with the short wire connecting it to the transmitter at the top constitute the complete ground lead -- which can result in an installed system that is functionally non-compliant with 15.219(b).

RF

 

[rfry]

That is just not a practical , statement, in our unit none of the control signals connect directly to the RF ground.

Keith, just wondering what the resistance/impedance is between the r-f ground terminal and the "GND" terminal of the AM1000. If it is very low then connecting an external wire to either of those points might give nearly identical results.

In your installation guide (link below) you recommend connecting the shield of the audio and power cables to the terminal on the transmitter marked GND.

This means that r-f current could flow along the outside of the shield, which would radiate even if nothing was connected to the r-f ground terminal of the transmitter.

Would you mind giving us your analysis of this?

http://www.am1000rangemaster.com/ExpandedInstallGuideforInstaller_3_10bw.pdf

RF

 

[Flying-Dutchman]

I don't think the FCC would allow Richard Fry to operate under
this part 15 rule. Doubt they'd let me use it either. This is
an exception for use by your average Joe.

God does not treat us all the same. Neither does the FCC. This
rule is clearly designed for non-technical people. Furthermore,
it is silent concerning the length of audio and power supply leads.

An FCC inspector goes to the home of a 16 year old boy. He says,
"You're in compliance son. Have fun! Keep it clean."

Same set up at Mr Fry's house or my home. "Hey! You have a
field strength meter and technical knowledge. You can't use that
rule. You are in violation. You can explain to Washington why you
should not pay $10,000."

OK. Average Joes have an FCC privilege that is denied to Rich and me. The privilege entitles them to have an ERP in the AM broadcast
band that is much lower than the ERP of my cordless telephone.

 

[Ermi Roos]

If that is true (I doubt it is), it may explain why Ken Cartwrigtht isn't allowed to use Section 15.219. He's no ordinary Joe. Just listen to his stream. It is very professional. He is a former radio personality, and he was a Radioman in the Navy.

I will grant der fliegende Hollaender that those who should know what they're doing might get more scrutiny from the FCC than "ordinary Joes."

 

[rfry]

If that is true (I doubt it is), it may explain why Ken Cartwrigtht isn't allowed to use Section 15.219. He's no ordinary Joe.

Ken Cartwright and everyone else should be able to use Section 15.219.

The FCC problems arise when operators do not understand and properly apply 15.219, but think and/or hope that they do. Of course, some may know that they do not meet Part 15, but are not concerned about it.

Obviously there is nothing inherently "wrong" or illegal about using unlicensed AM/FM transmitter systems that actually meet the FCC Rules applying to them.

RF