The AM HD all digital test, Part I

After reading this article in Radio World it seems the all digital AM testing completed last December was “nearly flawless.” This comes as no surprise considering that WBCN is owned by CBS, also an iBiquity investor.  Could there really be another result?  I think not.  But let us examine the technical aspects of the WBCN test itself.

WBCN is on 1,660 KHz in the expanded part of the AM band.  According to the FCC database, it transmits from a single 90.7 degree tower.  As such, the tower is likely either broad banded already or easily modified to be.  Also according to the FCC database, there are eight other stations licensed to 1,660 KHz, all of which transmit with a power of 1 KW at night.  This eliminates much of the interference issues found on the rest of the AM band.  It can be further noted, the problem with electrical noise is most prevalent below 1,000 KHz.  There is little wonder in the nearly flawless results.

From a technical standpoint, this is about as favorable a testing configuration as can be conceived for AM IBOC.  If AM HD radio did not work under these test conditions, then it would never work at all.  The actual data from the tests has yet to see the light of day and it may never be released.  This is likely due to the same reason the NAB will not release its technical improvement study on AM; we simply won’t understand it.

Near the end of the article someone (it is not exactly clear who) asks the NAB, “why the opacity?” For which the answer given is “to get stuff done.”  There is a fair bit of hubris in that statement.  Is the NAB now the technology decider for the rest of us?  I think not.  Shutting out everyone but a very select few rightly causes suspicion, something that the Radio World article acknowledges.

Accurate, real world testing involves more than using one technically favorable test subject.  In fact, the tests should be run in the most technically challenged environment to present meaningful data points in real world conditions.  Stations like a six tower directional on 580 KHz, or a 190 degree tower with a folded unipole on 810 KHz, or pretty much any class C AM station at night time.  These types of test will represent at least a few of the existing antenna systems and stations.  Will that happen?  It depends on whether the FCC will hold somebody’s feet to the fire and demand meaningful testing.

Much ink has already been spilled by various trade publications debating the future of AM broadcasting.  Most take the position that there are several technical issues which makes AM broadcasting problematic if not downright untenable.  There are indeed some technical issues with AM when compared with FM or IP based audio distribution.  There are also several ways that AM broadcasting is superior to both FM and IP based audio distribution.  The truth is that AM broadcasting’s issues are complex and involve technical, regulatory and operational considerations.

These can be broken down as follows:

  • AM is prone to electrical noise interference
  • AM is prone to co-channel and adjacent channel interference
  • AM has inferior bandwidth and thus audio quality
  • AM has poor signal quality
  • AM has low or no market share

All of these problems conspire to make AM broadcasting unprofitable, or so the narrative goes.  Does all digital AM HD radio really solve any of these problems?  From the WBCN test alone, results are inconclusive.

Transmitting a signal in digital format does not make it immune to noise or interference.  It simply masks the interference until the noise floor becomes too high causing excessive bit errors, at which time the receiver mutes.  Thus, with AM HD radio in a noisy environment, the listener will not hear static, that much is true, they may not hear anything at all.  Is this all or nothing reception an improvement?

AM broadcasting audio bandwidth problems are mostly self inflicted.  AM stations created loudness wars in the 60’s and 70’s, causing splatter and adjacent channel interference on older, cheap diode detector type receivers.  Receiver manufactures responded by limiting IF bandwidths to 3-4 KHz, slightly better than telephone quality.  The industry came up with the NRSC-1 standard which limited AM bandwidth to 10 KHz or less.  For a long while, AM radio receivers remained very poor.  This appears to be changing with newer receivers that are both more selective and more sensitive.  My Toyota has a Pioneer radio which has good bandwidth on AM.  Is it as good as FM?  No, but it is certainly listenable, especially if no other station is playing that style music.

That brings me to programming, which is the real crux of the issue.  Continued in part II.

Three generations of emergency communications

Even before CONELRAD was introduced in 1951, radio broadcasting was a critical part of the emergency communications infrastructure.  The government recognized early on the ability of radio to transmit data and information quickly, over large areas to the general public.  It works when all other systems fail, as demonstrated repeatedly over the years, the last of which occurred during Hurricane Sandy last October.  Massive destruction from flooding in lower Manhattan and shore side Brooklyn rendered the electrical grid, telephone network, the cellular network and the internet out of order.  Fortunately, enough radio stations stayed on the air and people used battery powered AM and FM receivers to obtain information.

CONELRAD poster, circa 1950's
CONELRAD poster, circa 1950’s

CONELRAD served two purposes; first, radio stations either re-tuned their transmitters to 640 or 1240 KHz or switched off the air. Then, each station that was still on the air would transmit for ten minutes, after which, they turned off and the next station in the chain would turn on and transmit for ten minutes. This was designed to confuse the Soviet bombers flying over the north pole on their way to incinerate us. Secondly, the CONELRAD stations were to distribute emergency information during and after said attack.

CONELRAD receiver
CONELRAD receiver

Recently, I found this CONELRAD receiver in a bomb shelter at a radio station. It dates to pre 1963, which is when CONELRAD was replaced by EBS.

EBS encoder/decoder
EBS encoder/decoder

EBS or the Emergency Broadcast System was a refinement of CONELRAD in several areas.  EBS used a two tone attention signal to unmute receivers and alert the public that something important may be happening.  Initially designed as a national system to warn of an impending attack, in later years it was also used by state and local governments to warn of other emergencies like weather, etc.

The current system is EAS or Emergency Alert System.

CAP compliant EAS
CAP compliant EAS

The Emergency Alert System was an advancement of the EBS in several areas.  Using SAME protocol in the message headers allowed stations to automate alert message relays.  This was driven by the desire for unattended operation.  The use of SAME also allowed many different types of messages to be filtered by alert type and area.  Each EAS unit also had an internal voice recorder.  All of this was upgraded in 2011 with the introduction of CAP, which would take email messages and generate computer voice alerts to be sent out over the broadcast stations.

Three generations of emergency communications equipment found at one facility.

The main problem with EAS CAP is it violates the engineering principle of KISS (Keep It Simple, Stupid).  It is an overly complicated system that relies on the internet, e-mail servers, the public telephone system and other infrastructure that may not survive natural or man made disasters, enemy attack or other disruptions.  Even something as simple as a national test proved to be problematic in 2011.

For a real emergency information network, the idea of WGU-20 has some merit.  Two or more well positioned medium to high powered LF stations could serve as a PEP distribution network and reliably cover the entire country.  With such a system, every broadcast station, cable head end and NOAA radio transmitter could monitor the LF stations directly, thus replacing most of the over the air daisy chain and or FEMA leased lines.  The advantages of LF is that it is fairly immune to HEMP, it goes a long way reliably, can have multiple redundant transmitter sites located within secure areas like military bases and uses time proven technology.  That would be a real, cold war solution.  But no, let us instead rely on a hodge podge of ISPs, TELCO leased lines, 3/4G wireless networks, SMS, satellite links, e-mail servers and the like, because: Hey!  It’s the digital age, we don’t need none of that stinking broadcasting crap.

Opportunity

My son and daughter are playing ice hockey this winter. Which means that every Saturday morning I have to get up very early and haul them off to the rink for practice and a game.  It is actually a lot of fun because I love watching them play.  Having played a certain version of pond hockey in my youth, it brings back good memories.

In any case, last week, after they finished their game and changed out of their hockey gear, my son wanted to watch the older kids play.  Thus, we sat down in the bleachers for a few minutes to watch the 12-15 year olds play against a traveling team.   Most hockey leagues are mixed, that is to say girls and boys playing on the same team.  Not to put too fine a point on it, but the girls can be decerned not only by their pony tails but also the pink stake laces or pink hockey gloves.  I also noticed that the girls seem to play a more cerebral version of the game, which is a joy to watch.

Not soon after we sat down, a fast break play developed at mid ice.  It was truly a thing of beauty.  A player from the home team intercepted a pass from the opposing team and took off down the ice.  She was followed closely by another player from her own team.  As they crossed the opposing red line, the other team closed in.  I watched the lead player move fast toward the goal then fake out the goalie, lifting her stick oh so much as she made the shot.  The goalie was completely fooled and dove for the non-existing puck, which was left on the ice for the following player, who neatly scooped it into the goal under the goalie’s leg.  It was over in a flash of white jerseys and pink laces.  I thought to myself; these are kids are great!  You do not have to watch an NHL game to see good hockey and sometimes the so called “professional” sports is overrated anyway.

Which got me to thinking about LPFM.  How many budding journalists, play by play announcers, DJs and presenters are out there waiting for an opportunity to show their stuff?  An opportunity that they may never get because most commercial and many public radio stations are locked into an increasing automation loop.  Locally originated programming is constantly being cut and replaced by satellite syndicated formats and or out of market voice tracking.  It is truly a shame, because the strongest leg that terrestrial radio can stand on is localism.

LPFM can be that opportunity to return radio to its community of license.  It will not be easy, clearly the rules were written to prevent LPFM from ever competing with commercial or even public radio stations.  Restrictive power levels, odious interference rules, and limited fund raising capability will keep all but the true believers and perhaps ignorant souls from attempting for a license.  It will be hard, but not impossible and the true believers will make a go of it.  The October 15th, 2013 filing window will very likely be the last opportunity for community organizations to establish a local radio station.  After that, the remaining spectrum crumbs will be divided between translator aggregators to create ever larger networks of mostly redundant content.

Terrestrial radio may well go through an evolutionary change.  As more and more broadcasters are finding out, once a license is owned, there is a great deal of expense in operating a station.  Things like employees and office supplies can be cut, however; towers need to be maintained, transmitters and antennas need to be replaced periodically, electricity bills must be paid, etc.  The larger the station, the more operating costs are involved.  Another serious economic downturn like 2008 and the crazy train will be off the rails.  The inexpensive to operate, volunteer run local LPFM may indeed be the last radio station(s) standing.  I have heard many decry this type of station as “amateurish” or “not professional.”  Here is what can happen if you give a bunch of amateurs a free hand:

Good stuff.  Big picture stuff.

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.

Or

(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.