April 2014
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Part 15 Broadcasters

I am utterly amazed at the lengths that some people will go to to get on the air. Where there is a will, there is a way.  Part 15 refers to FCC Part 15 rules, which cover unlicensed operation. Such things as wireless microphones, cordless phones, garage door openers, WIFI, other intentional and unintentional RF generators like computers.  Subpart C deals with low power, unlicensed broadcasting.

There are several rules regarding unlicensed Part 15 broadcasting, the most often cited rules are 15.209, 15.219 and 15.239, which sets the signal strengths allowed for various frequencies.  For the FM band (88-108 MHz), the signal strength requirements are very straight forward;  it is 150 250 µV/m measured at 3 meters from the antenna. This results in about 200 foot radius from the radiator or antenna reception distance.  Slightly more can be gained by broadcasting in mono.

For the AM band (530-1,700 KHz) there are several different measurement criteria.  First, FCC 15.209 states that the signal strength for an unlicensed medium wave station shall not exceed the value of (24,000/F(KHz) which varies from a maximum 45 µV/m at 530 KHz to a maximum 14 µV/m at 1,700 KHz measured 30 meters from the antenna.

Medium Wave broadcasting lends itself well to power line transmission, also known as carrier current.  There used to be many carrier current college radio stations in the country as it was a very easy way to broadcast to a limited area without the expense of a license and large transmitter.   There are still some carrier current stations out there, but many have gone dark.  For carrier current stations, the signal strength requirements can be found in FCC 15.221, which states:

(a) Carrier current systems and transmitters employing a leaky coaxial cable as the radiating antenna may operate in the band 525–1705 KHz provided the field strength levels of the radiated emissions do not exceed 15 µV/m, as measured at a distance of 47,715/ (frequency in kHz) meters (equivalent to Λ/2Π) from the electric power line or the coaxial cable, respectively.


(b) As an alternative to the provisions in paragraph (a) of this section, intentional radiators used for the operation of an AM broadcast station on a college or university campus or on the campus of any other education institution may comply with the following:
(1) On the campus, the field strength of emissions appearing outside of this frequency band shall not exceed the general radiated emission limits shown in § 15.209 as measured from the radiating source. There is no limit on the field strength of emissions appearing within this frequency band, except that the provisions of § 15.5 continue to comply.
(2) At the perimeter of the campus, the field strength of any emissions, including those within the frequency band 525–1705 KHz, shall not exceed the general radiated emission in § 15.209.

Finally, there is Part 15.219, which states:

(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.

Thus, there are several different ways to look at Low Power AM (LPAM) broadcasting.  In all cases, LPAM stations are not to be employed on the same frequency of an licensed AM station within its protected contour.  Part 15.219 appears at first to be contradictory to 15.209 which sets a specific signal strength value.  On reading the FCC’s recent NOUO and NOVs it appears the 15.219 is an exception and is left deliberately ambiguous, somewhat cryptically noting:

Another exception for some transmitters operating in the 510 kHz to 1705 kHz band is found in 47 C.F.R. S: 15.219. Specifically, Section 15.219(b) of the Rules states “the total length of the transmission line, antenna and ground lead (if used) shall not exceed 3 meters” (see 47 C.F.R. S: 15.219(b)).

From FCC EB-FIELDWR-12-00001143

Thus, from a technical and legal standpoint, which criteria will an FCC inspector use if they are looking at a possible violation with an unlicensed LPAM station?  In at least one case, it appears to be up to the inspecting officer.

With a well designed 3 meter (9.84 feet or 118 inches) vertical antenna and good ground system, it is very likely that a 100 mW station, particularly on the upper part of the AM band, could carry up to a mile or so, depending on the local ground conductivity.  There are several cases where multiple LPAM transmitters have been chained together, creating a SFN (Same Frequency Network) which covers a significant geographical area. This is a video showing two LPAM transmitters synchronized in Sioux Falls, SD.

Pretty amazing considering all the power lines and such.  Then of course, there is this, which shows that they might not be operating at 100 mW after all.  I don’t know at which point they began operating above the legal threshold, perhaps that video was taken during legal operation.

Even so, it is a very interesting concept, when one considers using a battery, solar panel, wireless LAN bridge and an AOIP device such as the Barix Extreamer to connect transmitters. There is one particular FCC certified transmitter that allows external synchronizing from a GPS source or by chaining the units together on a RS-485 buss. I have spent several days driving around and listening to static on 1,700 KHz, much to the annoyance of my wife and children.

There are several sources of information regarding LPAM broadcasting:

Those are just a few, if you know of others, leave them in the comments.  One thing to note:  If you are going to broadcast LPAM, make sure that you can demonstrate compliance with either 15.209 or 15.219.  Any type of unlicensed station that broadcasts with a regular schedule  over significant coverage area will be noticed.

If you are a licensed broadcaster and are concerned that a legally operating Part 15 station is going to cut into your market share, you are simply doing it wrong.

The FCC LPFM plan

FCC moves ahead on a couple of different fronts in the LPFM battle.  Cliff notes version:

  1. The 2003 translator filing window question.  The FCC has more or less stuck with it’s plan to keep a minimum number LPFM channels available in the top 150 markets.  This also includes a 50 application limit for the country and no more than one application per market per applicant.  Where conflicts occur, translator applicants get the chance to demonstrate how their application would not preclude LPFM opportunities.
  2. Modifies (eventually eliminates) the May 1, 2009 cut of date for cross service (AM to FM) translators.
  3. The establishment of new LPFM allocations under the criteria of disregarding the third adjacent channel contours.
  4. More stringent requirements for local programming and ownership, especially as a determining factor for mutual LPFM applications.
  5. Allows LPFM stations to own translators.
  6. New class LPFM is established; the LP250.  The 250 watt LPFM stations are designed mainly for areas outside of top fifty markets or for previously licensed LP-100 stations that want to upgrade provided the minimum separation contours are met with existing stations.

The FCC has included the proposed rule changes as appendix A of FCC 12-28.  Standard FCC comment and reply windows apply.

Looks like things are moving along pretty fast.  Others have speculated at a filing window sometime later this year, I’ll not do that.

Local Community Radio Act

The President has signed the reconciled bill into law, it will be published to the national register.  FCC Chairman Julius Genachowski promises “swift action” to get the new rules in place.   If this law leads to a bunch of new, live local community radio stations springing up across the country then it is a welcome thing.  With all the rumbling in congress about cutting public radio funding, LPFM may have some big shoes to fill.  I have to admit, I am generally a supporter of public radio, however they have gotten off track (full of themselves) in the last few years.

There are many different requirements placed on the FCC by the LCRA to thread the LPFM needle around translators and full power FM stations, so it may take a little time to craft new LPFM rules, however, I’d expect to see a filing window sometime in 2011.

If you are considering a LPFM station and are eligible for a license, take a peak at Prometheus Radio Project, which has a wealth of information about LPFM station building.

If you need a good engineer to file paperwork, specify equipment, consult about transmitter locations, towers, antennas and so forth, drop me a line.  You can find my info and contact information in the About section.

Future of AM radio

It is clear to me that radio is changing, in some ways it is changing for the better, in many ways it is changing for the worse.  In spite of many bad business decisions made by over priced MBAs, large consolidated radio groups seem to be hanging on, if only by their finger nails.  It is very likely that the investment banks, who have the most to loose, are not interested in seeing their loans written off in a bankruptcy proceeding.  As we all know, the consolidators that paid multiples of 15 to 16 times cash flow for stations, way over extended themselves.  There is no hope that values will ever return to those levels, so the banks are now in the radio business.

Sure, the banks are not the owners of record, and the FCC never would consent to transfer all those licenses to so many investment banks. However, they are calling the shots, making “suggestions” on how best to run things.  Offering perhaps a 1/4 percent reduction in an interest rate if the expenses can be reduced below a certain level.  Unfortunately, for the communities like Ellenville, NY, their local radio station means nothing to the banker living in Manhattan.  It is a number, and more than likely, a negative number on a spreadsheet.  It means nothing to the group owner in San Antonio, other than some miscellaneous real estate assets.  Same can be said for all the radio stations in the Hudson Valley if not the entire country.

Why is this important?  I mean, who really cares?  The apparent answer is no one seems to care.  Local news, or what used to be local news such as town board meetings, high school sports scores, police blotter, and all of the many other small town things do not get the hearing they used to.  Town boards; well if no one shows up for the meeting to pass the new zoning laws, so be it.  School boards; sure, raise the taxes, most home owners will just pay the new higher amount and not say anything.  It is for the children, after all.  Seems that the local constabulary is spending more time at the Dunkin Donuts than out walking around checking doors?  Thats the way it goes.  With the demise of local newspapers, detailed in a previous post, who is keeping an eye on things? Who lets the community know when something doesn’t pass the smell test?

Receiver tuned to local AM station playing good sounding music

Receiver tuned to local AM station playing good sounding music

A small AM radio station can be made profitable, just not at the margins expected by the big boys.  There is a niche for perhaps 1 KW or 5 KW non-directional station with it’s own real estate that is not in too bad shape can be turned into a community radio station.  Those type stations are fairly low maintenance, most have some type of PSRA and PSSA to keep them on at least during drive times if they are daytimers.  Others have minimal amounts of night time power.  Almost all of them cover their city of license, even with small night time powers.

I have been looking into good quality AM radio receivers and there are a few out there which are not too expensive.  Most GM car radios and older Chrysler radios have good AM radios.  A group formed to promote AM radio, ensure that auto makers install radios that are at least as good as their older versions, work with manufactures to make better small table top receivers and such would go a long way to improving the unjustly bad reputation that AM broadcasting has received.  Further, working with the ARRL (amateur radio) to reduce and keep noise levels from things like BPL and other noise making technologies that do not comply with current FCC regulations would also help.  It is true that our environment has become electrically noisier, one might not be able to listen to the 50 KW clear channel station 500 miles away, but the local station should come in well enough to enjoy, especially if the programming is good.

FM radio is becoming over crowed with translators, adjacent channel HD radio interference, LPFMs and whatever else can be shoe horned into the band.  The quality of FM is set to decline precipitiously in the next few years.  It seems that with the right combination of good local programming, good receivers and radio station owners/operators that are not looking to get listed on the NASDAQ, small AM stations could survive, if not thrive on the business that the big stations turn away.

There are a number, a small number, of stations already doing this.  As long as there is free local news and free quality programming, people will listen, no matter what band it is being broadcast on.  Free trumps paid any time, any day.

WOVV, Ocracoke, North Carolina

Community radio station WOVV signing on:

They are not there yet, according to their web site, anticipated sign on is not until spring of 2010.

Remember when all radio stations were community radio stations?  The CNN report now calls this “old-style radio.”  It is sort of funny how these little radio stations, built mostly by volunteers with donated money, get it. A radio station is supposed to be about community service. It is sad that broadcasters with both the means and methods to reach these isolated people have ignored them.  Because, you know, there is very little money in community service.

About community radio

Because of this post, I have received some e-mail asking why I am against community radio.  I am not.  In fact, I support community radio.  I think that community radio done well is a wonderful tool in our democracy, giving a voice to those that are watching government.  It also promotes other locals interests, events, music, etc.    I would like to see more failing stations bought by community broadcasters and turned into something that is a public trust and responsive to the local population.

What I was trying to get at in the previous post was that over crowding the FM band with more and more small signals will degrade it.  There is no ifs, ands or buts, removing third adjacent protections on the FM band will increase the noise floor.  This will lead to more interference on the average FM radio, which will lead to more people getting fed up and tuning out.

Here is why:  You cannot change the laws of physics.  FM transmitters have output filters that attenuate side band energy, that is to say, energy transmitted on 1st, 2nd and 3rd adjacent channels.  A 50,000 watt FM station on 100.3 MHz will have side band energy on 100.1, 99.9 and 99.7 MHz as well as 100.5, 100.7 and 100.9 MHz.  Due to the limitations on the components used to construct those filters, they can only be designed with the accuracy of the components used.  In other words, most electrical components have a tolerance given in percent, example +/- 10%.  That means that the value of the component will change, usually because of heating.  Therefore, output filters cannot be constructed to limit emissions to only the main channel and say one adjacent channel, they would drift off frequency.

Also, creating a brick wall filter that cuts everything off at the second adjacent channel will cause distortion of the RF signal on the main channel.  With analog AM and FM transmitters it cannot be done.  Digital transmissions are another story, but that is not what we are talking about here.

That is an engineer’s point of view.

One other thing about adding hundreds more LP FM signals.  There should be something that stipulates most (say >50%) of the programming be locally originated.  Recorded for later playback is fine.  Having thousands of LP stations broadcasting the same syndicated shows or running voice tracked automation 24/7 would be a recreation of the AM band as it currently exists.  If you want to listen to that, then it already exists, help your self.  I, on the other hand, would like to avoid the AMization of the FM band.

That is all.



Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

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