fcc – Engineering Radio

All Digital AM?

I have been reading, with interest, the saga of HD Radio on the AM (AKA Medium Wave) band. First question; if it goes all digital, will we still call it AM? Of course, there are other questions and concerns:

The proprietary nature of HD Radio, AKA MA3 or NRSC-5D as they are now calling it, is problematic. Xperi, the latest patent owner, currently (their word) has agreed to waive licensing fees for AM station owners who install their system. Is this a limited-time deal for early adopters or in perpetuity for all stations?
The NRSC-5D tests on WWFD, Fredrick, Maryland are hopeful, but as I pointed out before, it is one station with a well-functioning antenna system. Many AM antenna systems are defective either in design or due to deterioration. Is the FCC going to start policing the AM band again to cure these self-inflicted wounds?
Of course, the NAB wants zero oversight on the entire adventure. Under their proposal, small ownership AM stations would have a difficult time remediating interference issues from all digital co-channel stations by eliminating any required notification period, as proposed by the SBE.
The NAB also wants to nix a 1 Hz carrier frequency requirement, which would help with both the analog and digital interference issue, saying it would be too expensive. I disagree. In this day of universal GPS timekeeping, it would be easy to implement this on all modern transmitters, especially if they were already installing an HD Radio exciter.
Denis Jackson’s Radio World Article states that reliable coverage can be had out to 0.1 mV/m. This seems very, very optimistic given that ambient electrical noise (non-broadcast related) on the AM band is at very high levels and still climbing. Further, once the all-digital conversion starts, more and more co-channel digital interference will happen, likely cutting down that contour to a great extent. It works now but may not work later. These types of statements seem naive or perhaps disingenuous. Again, WWFD is one digital signal in a vast ocean of analog carriers.

While I am skeptical of some of the statements made in various articles and comments before the FCC, I do believe that converting the Medium Frequency band to all digital will have benefits. The BBC DRM tests carried out in 2007 (The Plymouth DRM long term trial) show that digital on MF can work. DRM has been implemented in various countries with good results.

Getting rid of the hybrid IBOC/Analog is a step in the right direction.

My concerns are the small owners who are still making a go of it on AM. Those guys still doing community radio and serving the public interest. If they choose to wait, are they going to get buried under a digital dog pile and then have to pay the full license fee later? Something like that might be the end for them.

HD Radio in and of itself is not the panacea for the AM band. Other things have to happen to make it work right. The SBE speaks extensively about ambient noise on the MF band. They are entirely correct. In addition, there are many, many AM stations that do not have compliant antenna systems. There are stations operating a DA-2 system full-time on the night pattern. There are stations operating a DA-2 full-time on the daytime pattern and power. There are stations that are supposed to turn off at night, which stay on 24/7. There are stations not reducing power to nighttime levels. The list goes on. Simply putting digital carriers on everything will not reduce station-to-station interference, especially at night.

I am cautiously hopeful that the FCC will look into the ambient noise problem, which simply cannot be over-emphasized. They would also need to re-invigorating the Enforcement Bureau. Since they closed down most of their field offices, it has been kind of a free-for-all out here.

Status of AM revitalization

It has been about five years since the AM revitalization initiative was first proposed by the FCC and about five years since the first rules changes took place. Those rules changes included:

FM translators for AM stations
Allowing stations to use MDCL (Modulation Dependent Carrier Level)
Changing some of the antenna radiation efficiencies requirements
Changing some of the allowable interference towards other stations requirements
Loosening some rules regarding proofs, MOM, nighttime coverage over the city of license, etc

Things that were not addressed:

Receiver quality and technical advances
Ambient noise levels on Medium Frequency (among other) bands
HD Radio or any other digital modulation scheme

Things that were discussed then changed subsequently as a separate initiative:

The main studio rule, which was eliminated for all broadcasting stations

What has been the net effect of these changes? Has any of this revitalized AM radio? The net effect has been approximately more of the same. There have been many stations that have applied for and received licenses for FM translators. Those stations, in most cases that I am aware of, receive some benefit of extra revenue because of this. Stations with carrier power levels of 10-50 KW have taken advantage of MDCL technology to save some money on their electric bill. Nothing wrong with that.

For stations that use a directional antenna, proofs of performance and other DA matters with the FCC have become slightly easier. Medium Frequency (MF) directional antennas are very large, require a lot of land, are expensive to build, license, and maintain. I know of several stations which have downgraded from a class B station with a directional antenna to a class D station with a single tower and greatly reduced nighttime power. Those downgraded stations certainly benefit from an FM translator.

I have heard from more than one AM station owner who says after four years, they are going to “turn in their AM license and just keep the FM.” I am sure that they are not informed regarding translator rules. Perhaps, however, the FCC will allow this in the future; a sort of back-door commercial low-power FM station classification.

The AM band zenith occurred in November of 1991 when there were 4990 licensed AM stations in the United States. As of June 30, 2018, the total stands at 4633. That is a decline of 357 stations. There are currently 90 AM stations listed as silent. That represents a decline of approximately 9 percent or less than 1/2 of one percent per year.

The last number of AM stations actually transmitting HD Radio that I found was approximately 110, which differs from the iBiquity (and FCC) number of 240. The FCC database includes stations that are currently dark or stations that were transmitting HD Radio at one time but have since turned it off. Either way, it is a small percentage of licensed stations. As of this time, AM HD Radio appears to be a non-starter. In other parts of the world, Medium Frequency DRM seems to be doing well. The difference seems to be that the DRM operation is all digital and the digital carriers have a much higher power level than that of the hybrid AM HD Radio being used here.

Of those 4633 standard broadcast stations, approximately 260 belong to iHeart radio, Cumulus owns approximately 120 and Townsquare owns approximately 80. That accounts for 460 stations. The remaining 4000 or so stations currently on the air are owned by medium-sized corporations or individual owners. The reason for the distinction; I have noticed that large corporate owners tend to concentrate resources and effort on those licenses that will make the best return, e.g. FM stations. Of course, there are a few exceptions to that trend, often in major markets.

Of those 4000 or so remaining AM stations, most seem to be treading water. They are making enough money to stay on the air. There are a few AM stations that are doing remarkably well. Those are the ones with primarily local content. The vast majority of AM stations are running some type of syndicated talk. News/talk and sports radio are the two most common formats. Conservative news/talk seems to be the bread and butter. Liberal news talk has been tried, but none have succeeded.

Last May, the Supreme Court overturned the Professional and Amateur Sports Protection Act of 1992. That federal law prevented gambling on outcomes of professional and college sports games. With the overturn of that rule, individual states can now legalize sports betting. It will be interesting to see what states allow legalized sports gambling and whether that has any effect on the various sports radio formats. I can see where individuals and odds makers may want to get good inside information regarding team dynamics and so on. The sports network that can furnish such information may be in a good position to carve out a niche.

Music can and does sound good on AM when it is done correctly. There is a great misconception that AM fidelity is poor. That is not necessarily so. There are a good many AM receivers these days that have much better bandwidth than the previous generation receivers. I am noticing that car radios in particular sound much better. Yes, there are still problems with electrical noise and nighttime interference. There are still technological improvements that can be made for analog AM on the receiver side.

In summary; the revitalization efforts have benefited some AM stations in some areas. The truth is, that many AM stations have been let go for so long that there is no saving them. Other AM stations that are still viable are making a go of it. In nautical terms; there is six feet of water in the hold, the pumps are working and the ship is not sinking… for now.

The side mounted FM antenna

In an interesting development, the FCC has taken notice of some pattern distortion from the side-mounted FM antenna of KFWR, Jacksboro, Texas. For those, like myself, not familiar with Texas Radio, that is in the Dallas/Fort Worth market. The crux of the issue is co-channel interference to KCKL in Malakoff, Texas. These two locations meet the spacing requirements in 73.207 (215 km). The issue is with the side-mounted ERI antenna and what appears to be intentional pattern optimization.

From the FCC order to show cause:

ERI’s president, Mr. Thomas Silliman, acknowledging that KFWR’s antenna “was mounted in a favorable direction, but… has not been directionalized and therefore is legal.” Mr. Silliman adds that the custom lambda tower at the top of the new KFWR tower was specifically designed for operation at KFWR’s frequency of 95.9 MHz, and that the tower’s lattice structure is “repetitive at the half wave of the specified FM frequency.” Thus, “if one picks a favorable mounting position on the tower, every element in the array sees the same favorable mounting result. Mr. Silliman also states that vertical parasitic elements are used to make the vertical radiation pattern “more circular” and reduce the vertically polarized gain to the east. In a subsequent pleading, ERI elaborates that its computed values “are relative to an RMS measured field of 1.0.” Mr. Silliman concedes that the mounting of the antenna on a certain tower face constitutes “pattern optimization,”arguing later that this is a common practice used by all antenna manufacturers, but states that it is the ERI’s policy “not [to] increase the directivity of the antenna pattern.”

The FCC concludes that the directionality of the side-mounted antenna, in this case, is clearly intentional. The radiated power towards co-channel KCKL was calculated to be 274.5 KW, which is in excess of the 100 KW limit, and orders KFWR to reduce TPO from 25 KW to 9.1 KW.

We have lots of these out in the field:

Side-mounted Shively 6810 antenna. WSPK, Mount Beacon, NY

In fact, I believe the majority of our FM stations use side-mounted antennas. Some of them are mounted to a leg and some are mounted to a face. Usually, I try to place the antenna on the tower so that the bays are facing the desired audience. This information is given to the manufacturer when ordering the antenna so that proper mounts can be furnished and the mounting distance between the tower and antenna properly calculated. That is about the extent of any “optimization” that is allowed.

As the FM band gets jam-packed with FM signals, this may become more of an issue in the future, particularly around dense signal areas around major metropolitan areas.

Filing an STA

FCC rules stipulate that when a station is operating at variance from its licensed parameters for more than 10 days, Special Temporary Authority (STA) is required. The reasons for requesting an STA are varied but could include things like:

Damaged transmission equipment
Loss of transmitter site or building use
Loss of tower
Eviction
Facilities upgrade or renovation
Natural disaster

The loss of the transmission tower at WUPE-FM falls into one of those broad categories. Thus, we have filed an STA with the FCC for temporary transmission facilities while a new tower is being constructed. Since the old tower is completely lost, we specified a new tower location, new height above average terrain (HAAT), new ERP, and environmental certification. To gather that information, several steps were needed:

Obtain a new tower location. This was done with a GPS receiver and verified on itouchmap.com. Once the NAD83 position was obtained, it needed to be converted to NAD27 for the FCC filing. The FCC has a conversion tool on its website.
HAAT calculation is fairly simple, use the HAAT calculator tool on the FCC website. For this, the antenna radiation center height Above Mean Sea Level (AMSL) is needed. Using a topographical map, find the ground level AMSL, convert it to meters, then add the radiation center height above ground level (AGL).
The Effective Radiated Power (ERP) calculation is also simple; Transmitter Power Output (TPO) minus system losses (transmission line and antenna gain). It is easiest to do this in dBm, e.g. convert the TPO from Watts to dBm, then add or subtract the gain or losses in dB, and convert the final product back to Watts.
The environmental statement is slightly more tricky. Basically, the filer is certifying that the STA complies with all environmental regulations including OET-65 (RF exposure limits). Since the temporary antenna is significantly lower than the original, some investigation is required. For this, there are two methods to demonstrate compliance; ground measurements with a NARDA meter, or RFR worksheets which are a part of the broadcast station renewal form, FCC-303s.

I have taken the RF worksheet sections out of the 303s and separated them into the FM RF Worksheet and the AM RF Worksheet. These worksheets are not effective for large tower farm-type sites where there are too many variables and RF contributors to be accounted for. The calculations on the worksheets are not conclusive, however, if the facility in question falls under the limits, it is generally accepted as being in compliance. Taking ground measurements with a NARDA meter is the definitive method for determining RFR compliance. Since this is a relatively simple site, the worksheet calculations should be sufficient.

The worksheet calculations show that the RFR is within both the controlled occupation limits and the uncontrolled general population limits.

The position of the new temporary pole was verified on itouchmap.com:

It is never good to be operating at a varience from licensed parameters without notification of the FCC. Such things could lead to fine or other problems for the broadcaster.