FCC and the PART 15.219

from MRAM 1500 kHz

Know where you're commin' from kint98. Everybody seems to boast 1/2 mile, 1 mile, 2 mile range but as a legal Part 15 I'm certainly puzzled. The FCC pre-defines your field strength on the AM band as not to exceed 24,000 micro volts divided by your freq in kilohertz at a distance of 30 meters from the antenna. So my 1500 kHz transmissions should be no more than 16 microvolts per meter measured at 30 meters from the antenna. Given the efficiency of a legal antenna system, that's about all you're gonna get. I base that on info I've read on other sites.

So let's say I have a fantastic (legal) antenna system and manage to actually radiate a few milliwatts of my signal applied. If I did that I'd be violating the field strength limit even if my transmitter was FCC approved.

There's a lot of things one can do to improve their FCC approved transmitter range. But, more range means a higher field strength and bingo, you're in violation. I was surprised to hear of a supplier of "cadilac" Part 15 transmitters advise someone to add a ground counterpoise system to their antenna. Grounding is a real grey area for Part 15 AM but it would be hard to argue away 60 or so copper wires strung in the air below your antenna as not being part of the antenna.

The key here I think is make sure your output is clean, reduce the harmonics and keep your frequency away from local commercial stations. Don't broadcast foul language and political rhetoric that infuriates people. After all, unless someone is looking for you only the people you tell about your station will be listening. Part 15 is mainly concered with mitigating interference from unlicensed transmitters. If you're not causing interference, most likely no one will notice.

I'm an Advance Class Amateur Radio operator. I have an FCC commercial Radiotelephone General Class license and I've been playing with Part 15 AM since I was 10 years old. I'm 53. And I still love it.

As both of you and I have found, this can get pretty messy when trying to interpret and follow the part 15 rules.

Here's my take on it.

The 200 foot limit is not writtten into law, it is a illustration cited in a public notice on the subject and states the range one can expect.

There are two governing parts of part 15. One is based on field strength alone. The second part can be used in lieu of the field strength limit.

This second part defines the antenna, ground, transmission line, and power input limits. You may operate under either of these rules, and are not required to operate under both, thus if you are compliant with antenna, power, etc., you do not need to observe the field strength limit.

It appears that through clever engineering of antennas some AM broadcasters have legally extended the range of their signals beyond what was apparently the original intent of the FCC rules.

I don't know, but I suspect that they are producing field strengths beyond the limits, but they are legal if following the antenna, etc. limit rules.

I don't have all the part15 numbers before me at present but you can pursue them by reading through the part15 rules which apply to operation in the AM broadcast band.

What do others think?

Neil

(BTW I am an also an amateur operator who got started when I was 14 with part 15 AM and still (46 years later) have fun with it.)

by MRAM 1500 kHz

That's the problem. Everybody has their take on how to interpret the rules. Not to many really know and it's a shame that legal stuff has to be so complicated. After all, most of us are trying to be legal with our Part 15 stations, and for the most part we really think we are.

Well now I've done it. I fired off an email to the FCC for clarification. Is it necessary to satisfy 47 CFR 15.209 (field strength rule) if I've satisfied 47 CFR 15.219 (input power and antenna limits) for an AM band Part 15 operation.

In the FCC document "Understanding Part 15" they state early on that 15.209 (field stength rule) applies to ALL Part 15 transmitters using frequencies above 9 kHz except where special provisions for stronger emissions have been made for specific uses. So they are saying that regardless of other requirements, emission limits still apply.

At least, that's my take on it. Let's see what they have to say. I'll carbon y'all if and when they reply.

Bob

Bob,

If you are able, look at the actual Part 15.215 rule. This part lists alternatives (such as 15.219) to the general field strength limits in 15.209.

I edited this post to include the text:

Section 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.

This is why in my post I said that you can operate part 15 AM under either of these sections and do not have to operate under both.

Since most of us cannot measure the field strength, we operate under 15.219 (as allowed by 15.215) which is the 100 mW/3 meter rule.

Let's see what the FCC says.

Neil

by MRAM 1500 kHz

By golly Neil, I never looked at it that way and I believe you are correct. It will be interesting to see if the FCC replies to my inquiry and to see what they have to say.

Just goes to show why it's always good to have a second pair of eyes look over something for ya.

Now, let's talk about those RF grounds again and how to make them fade into that grey area.

Thanks,

Bob

Yes, that illusive ground. Here's what Keith Hamilton has on his Rangemaster website under Techical/Ground about a ground wire:

There are a lot of questions about whether or not the ground wire is to be included in the FCC 3 meter limit. I have discussed this with the top FCC enforcement official in the DC office. He has told me that the FCC gives the designer latitude to determine what ground is as long as it is reasonable. We have no problem calling the tiptop of your ground wire at the transmitter binding post "ground" as long as you use a massive wire, (#12 or #10) intended for grounded purposes. We do not feel that in this case the Ground cable is included in the 3 meter limit. JimB

That's why I connect my 2 inch "ground wire" to the 20 mast. Naturally I ground the base of the mast for lightning purposes.

WDCX AM1610 Part 15
John
Owner-Operator-Chief Engineer-Program Manager

Hi,

On another board, one of the posters posed the ground question to the FCC and received a reply. The reply said that they do not accept elevated grounds.

Go to Radio-Info.com and look for the post titled "FCC response to Part 15.219 3 meter rule" posted on 1/6/06.

Neil

Here's the deal. As part of the FCC Certification process a manual is required as part of the submission process. The installation instuctions clearly state the antenna and ground mounting details including roof mounting with a long ground The Hamilton Part 15 Transmitter is certified. Case Closed.

WDCX AM1610 Part 15
John
Owner-Operator-Chief Engineer-Program Manager

by MRAM 1500 kHz

Ok. So we all are concerned by the antenna system ground wording of Part 15.219. As John stated, the FCC included the installation instructions as part of the certification which allows for elevated ground connections (wonder what the definition of that is.) So it would seem to be OK according to that at least for the RangeMaster.

My question: If I choose to operate under Part 15.209 and can accurately determine my field strenght to be in compliance, am I not restricted to the 100 mw / 3 meter rule? Ok, Ok, you may get more field strength (signal) under 15.219 but I'd love to see how a larger antenna coverage pattern would compare even at a lower field strength. I have an engineer friend that works for a local radio station who'd verify my signal to be compliant.

If nothing else, my transmitter could be in here rather than out there.

Hi,

mram1500, if you can certify by measurement that your field strength does not exceed the limits specified in part 15.209 then you are operating under that rule. You can run any power you want with any antenna you want as long as the field strength at 30 meters is legal.

For John, I think the FCC requirement for submission of manual is to insure compliance with the requirement that the manual includes the required statement regarding part 15 devices. If you know that they are evaluating the installation and operating instructions, I will be interested in knowing this.

I have stated before that the only defensible definition of the point of grounding is where the wire goes into the dirt. Ask an electrician where your home power system is grounded. Ask a radio engineer where his antenna is grounded. Ask an amateur radio operator where his station is grounded (mine is grounded at the electrical service entrance ground stake). Ask lightning where ground is...I don't think it is the top of the tree that was struck.

More important to this post, ask yourself why the FCC would limit the ground length. My answer is that the ground lead above the dirt radiates a signal and the FCC knew this when they intended to limit the range of part 15 AM transmitters. Why then would they allow any ground scheme such as a 20 foot mast which increases the field over what they intended?

In summary, why do you think it is called ground?

Neil

No matter how massive an exposed conductor is used to connect the tx chassis of an elevated P 15 AM tx and ~3-m radiator above it to the ground plane at/in physical earth -- that conductor will radiate.

True r-f ground conditions don't exist anywhere along the length of a conductor that is not buried. The DC resistance of that conductor when measured end-end may be just milliohms, but the r-f impedance presented to the tx will be greatly different -- and that is the issue here.

The r-f current flowing through that conductor leading to the ground plane easily can generate more field strength than the 3-m "antenna" above it. Radio-frequency current flowing through a conductor is the basis by which all radiators (antennas) function.

Believing that such a conductor is "ground" doesn't change the fact that it really isn't an r-f ground, it only leads to the r-f ground.

Engineering analysis shows that, in fact, the conductor leading from an elevated Part 15 AM tx to its connecting point at the surface of the earth is part of the radiating structure of such an antenna system. Therefore that entire conducting path IS the "ground lead," and operationally it is part of the antenna length defined by 15.219(b).

by MRAM 1500 kHz

Rich,

Excellent post. And Neil, if that's the case, I'm gonna try it!

I've been reading up on the EH-Star antenna. Similar to a cross-field antenna, it's a short, fat dipole that uses cylinders rather than wire or tubing for the radiators. The theory is a little complex and hard for old school to accept but many Hams claim fair to good results. If it works, it would be of great benefit to AM broadcast stations as it is a very low profile antenna.

A big problem they had was RF on the outside of the coax shield. The big controversy was the claim that the coax shield was actually where the antenna was radiating most of its signal. Because of that either a choke (made of several turns of the coax itself) or a ferrite bead balun is placed very close to the antenna to stop or greatly reduce the RF from radiating off the coax.

The next step was to feed the antenna in a balanced configuration rather than unbalanced. They claim that this eliminated the RF on the coax problem just as does feeding any dipole antenna using a balun.

My question: Do we know of any Part 15 systems that have tried anything similar to an EH-Star antenna? Not necessarily that antenna but perhaps a center loaded dipole that could be fed in a balanced configuration. That should pretty much eliminate the RF on the feedline if the theory works for short, fat dipoles.

Bob

Since I started this Ground thread with a quote from Keith Hamilton's Rangemaster manual, I'd just like to point out again what is said there. No arguments as to what a true earth ground is. What is said is that the Chief FCC Enforcement Officer in Washington DC says that they give some LATITUDE here and accept the ground to be at the transmitter if a wire size #12 or #10 is used. Sort of a gift from the FCC if you show yourself to be a good fellow. It's known that some local inspectors don't allow the ground wire at first glance, so I keep a copy of this paragraph from Keith's website printed out to show Washington's view should an inspector show up. One other point. Keith continues on his site with instructions to keep the ground wire away from all other metal, ie, use standoffs if the transmitter is on a metal mast or tower account, for, as he puts it, the ground wire needs to develop some impedence. This surely is another radiator, yet he's been certified by the FCC. Phil at SSTRAN has told me that some of his customers have requested the FCC to inspect their setups using his mast grounding plans and they passed with no problem. I work part time for a local 1000 watt AM station, just celebrated my 50th anniversary there in Nov., and must say that the FCC needs to spend its time policing such places more than they need to worry about some poor fellow radiating 100mw a few blocks up the street. JimB