AM – Engineering Radio

AM Shut-downs

The big question; how bad is it?

The short answer; Not terrible, not great.

Short summary in a chart:

Service	Licenses Canceled	Licensed and Silent	Comment
Full Power AM	812	105	Since 1991*
Full Power FM	517	88	Since 1991
Low Power FM	502	51	Since 2005
FM translator	1677	138
FM Booster	165	11	Since 1991

Summary of silent and canceled licenses

*1991 was the peak number of AM licenses. It also marks when the FCC record-keeping began tracking the license status of all services.

There are 10,846 full-power FM stations, 8,374 FM Translators, 1,910 Low-Power FM stations, and 373 FM boosters currently licensed as of this writing.

According to the FCC data, the peak number of AM stations occurred at the end of 1991 with a total of 4,985. As of August 2024, there are 4,303 stations. There are 105 AM stations licensed and silent.

AM station licenses are being surrendered to the FCC at an increasing rate in the post-Covid era. I like charts. It is fun to look at raw data sorted in different ways. Fortunately, the FCC’s license management system allows one to search for various categories e.g. “Full Power AM” and “License Cancelled.”

Here is a chart by year of the number of AM station licenses surrendered to the FCC:

Year	Licenses surrendered	States	Comment
1992	1	AR
1993	2	FL, MS
1994	1	GA
1995	0
1996	41	SC, VA, GA, KY, LA, FL, NC, TX, CA, OK, AR, MT, KS, AL, PA, TN, MS, IL, MN, FL, MI, UT, ME, IA	FCC 96-218 rulemaking
1997	33	SC, NY, CT, AR, GA, LA, NJ, AL, VA, FL, ME, AZ, MS, MD, CO, WV, MI, CA, NC, SC, TX, VT	FCC 96-218 rulemaking
1998	9	PA, NC, MO, CA, WV, TX, CT, AL
1999	11	CA, PA, LA, IN, NM, VA, NY, MD, TX, WI
2000	6	FL, CA, VA, WV, PA	Dot-Com crash
2001	12	IA, NC, SC, IA, AR, ND, CA, VA, RI, OK, OH
2002	14	MI, GA, TX, PA, IA, MI, AR, AK, KY, MS, MP (Northern Mariana Islands)
2003	15	CA, AK, MI, PA, MS, ME, CO, GA, KY, AL, CO, VA
2004	34	NC, GA, CO, MS, SC, PR (Puerto Rico), LA, MI, OH, TX, FL, AR, CA, UT
2005	11	TX, GA, CA, AR, IA, PA, MI, OR
2006	16	TX, PA, AR, MI, OR, MS, IL, MN, OK, WA
2007	9	GA, AR, TN, OR, VA, TX, MA, MO
2008	4	FL, MI, PA, AL
2009	7	MI, IL, OK, OR, LA, ID	Sub-prime mortgage crash
2010	7	NY, VA, TX, PA, AL, WV
2011	32	MS, AL, GA, VI (Virgin Islands), MD, MI, AS, TX, AR, IN, FL, TN, SC, NM, IA, NY, PA, LA, VT, NC
2012	25	MS, FL, LA, TX, DE, KY, TN, IN, AL, GA, OH, PA, IL, MS, NC, MI, UT, SC. FL
2013	20	MS, PA, OR, AL, MT, OK, TX, SC, NV, NM, NH, GA, TN
2014	22	SC, CO, AK, AS (American Samoa), IL, AR, PA, RI, GA. IN, MA, MI, TX, NY, MS, WY, AL, MT, VA, LA, MO
2015	21	AR, GA, WI, AL, NE, NV, HI, SC, NY, UT, MO, TN, KY, MA, IL, AR, AL, AK
2016	22	DE, SC, HI, WI, MS, AL, OH, NV, MT, GA, NY, MO
2017	19	NC, KY, CT, MO, GA, IL, TN, WY, NY, CA, OH, NH, PA
2018	18	MD, KY, GA, NC, IL, GA, MS, UT, VA, LA, NY, MT, AR
2019	33	AL, SC, OR, AR, TN, NC, WY, IN, KS, HI, WA, AL, IL, KY, HI, VI, VA, GA, LA, CA
2020	60	MO, NE, FL, GA, LA, ID, TX, MP, AR, AK, KY, IL, AL, NJ, TN, MI, SD, MS, VA, CO, OH, SC, NM, WI, ND, AZ, OR, MD, PA, NV	Covid-19 crash
2021	46	MI, FL, AL, NV, GA, NM, PA, AZ, IN, OH, TX, IA, OR, CA, VA, IL, TX, TN, CA, NC, LA, OR, AZ, MS, SC, WV, WA, PA
2022	21	FL, MS, AR, VA, MT, NY, KY, TN, SC, ME, NC, NM, MO, TX, GA, VT, PA
2023	188	TX, SC, MI, CA, ID, IL, OR, MD, MA, NM, AR, FL, KY, OH, TN, NC, LA, AR, CO, ME, MS, GA, WA, MI, OH, PA, VA, NJ, WI, NY, HI, NH, UT, IN, MT, SC, WV, IN, GU (Guam)	The Great Cancellation of May 4, 2023
2024	35	VA, AL, ME, LA, NC, MO, NY, SC, AZ, IL, NM, NV, WA, FL, TX, IN, WY, WA, KS, CA, MA, OH, NJ, AR, GA, CO, PA, VT	As of August 2024

US AM station cancelled licenses since 1992

A couple of things to note; there seems to be a two-year lag between any major economic downturn and a mass surrender of licenses. Covid-19 appears to be the exception. When the shutdowns came, clients canceled their advertising in mass causing a rapid end of already teetering businesses. In 1996, the FCC changed the rules on silent stations, limiting the time allowed to be silent to 12 months, after which the station license was canceled.

In 2023, the FCC performed a bit of housekeeping, canceling 188 AM expired station licenses some of which had been expired for decades. They performed the same thing for the FM band in October.

While every state and territory has at least one surrendered license, some states have more than average. Those tend to be mostly in the south; Alabama, Louisiana, Georgia, Florida, Mississippi, South Carolina, and Kentucky.

differed maintenance, AM transmitter site

Too many AM stations these days are dead men walking. It takes effort to keep an AM station on the air. Maintenance of antenna arrays, particularly directional systems, is expensive. Selling advertising is much more difficult than it is for FM stations. Local programming is expensive. The land under an AM tower is often worth more than the license itself.

4 Tower antenna system, WBNR, Beacon, NY

Land within certain city limits is a ripe target for developers. As more pressure mounts on station owners (taxes, zoning, etc) how long can they last before the inevitable happens?

Then there is the aging audience problem and in many smaller operations, the aging owners problem too.

The transition to digital modulation never happened. There are no AM stations running hybrid (MA1) HD radio. There are three AM stations that I know of that are running the all-digital (MA3) version of HD Radio.

In spite of those things, AM continues on.

Perhaps one reason; AM equipment is fairly simple in design and ease of use. Take away the electrical noise problem and it works well. AM radios are still ubiquitous in most houses, cars, hotel rooms, etc.

Many AM stations now have an FM translator, which is especially helpful if the AM station has to sign off at sunset or greatly reduce power. Some AM stations are simulcasting with full-power FM stations.

Crossed Field Antenna, Courtesy of Wikipedia

Are there any technological developments that would solve some of the issues facing AM broadcasters? More economical yet still efficient antenna designs that save space? A different modulation scheme that is still compatible with full-carrier AM and will work with older receivers (9K5R3E)?

Those question will likely remain unanswered. The FCC has shown no interest in allowing experimentation on the Medium Frequency band.

I Audited the RF Noise in my House

The largest problem facing analog AM broadcasting (and digital Medium Frequency and High Frequency broadcasting) is RF Noise.

Like most people, I have many modern conveniences that make my life easier than previous generations; electric lights, central heat and air conditioning, appliances like vacuum cleaners, microwave ovens, and whatnot. I enjoy the wireless internet, have an LED TV, use LED light bulbs, and get free electricity from my photovoltaic solar system. These devices can contribute to the high levels of RF noise found in most buildings. RF Noise which is the bain of AM broadcasting. Digital modulation schemes use variations in amplitude to transmit data bits. They are not immune to RF noise, they simply mask it better until they don’t.

I thought it would be interesting to isolate the various noise generators that may be present.

To make measurements, I used the Siglent SVA-1032X spectrum analyzer. This unit has a noise floor of -140 dB. My methodology is to turn everything off except the Device Under Test. Set the spectrum analyzer up for a wide band sweep, then narrow the bandwidth on any detected noise. Turn the DUT off to make sure that the noise goes away. Turn the DUT back on to make sure that the noise comes back.

The first thing I noticed; there is more noise during the daylight hours than at night. This is interesting. I thought it might be coming from my solar system, which uses individual inverters for each panel (so-called microinverters). These are wired to 240 VAC but have an internet gateway device that is in the house and communicates with the inverters using a power line data scheme. It turns out this was a minor contributor below the AM broadcast band.

By process of elimination, here are things that were not contributing to RF noise on Medium Frequency (AM band):

Cable Modem (Motorola MB7420 DOCSIS 3.0)
Router/WiFi gateway* (Netgear R6700v2)
GB Ethernet Switch (Netgear TLSG116E)
Dell Desktop PC’s (three models)
Dell Laptop PC (two models)
Android phones (two models)*
Phillips 4K LED large-screen TV (5PFL5604/F7)
LG LED computer monitor (24MK430H-B)
Refrigerator (Frigidaire FFTR1835VSD)
Stove (GE BP63D W1WH)
LG washing machine (WM3400CW)
LG clothes dryer (DLEX4501)
Bosch dishwasher (SGV68U53UC)
Dehumidifier (GE APEL70LTL1)
LED light bulbs (Sylvania 9W Ultra LED)
Generic incandescent light bulb
Furnace (fancy controller)
Furnace burner motor**

*These are intentional RF emitters

**The furnace burner motor made a small broadband RF signal on startup, likely the igniter which uses an electric arc. Once the unit was running, there was no further RF emissions noted.

The yellow line is the peak hold, the magenta line is the 100 sweep average and the cyan line is the minimum peak hold. I live out in the sticks; there are no streetlights, no stoplights for miles, the nearest cellphone site is four miles away, and houses are spaced far apart.

First, I measured the noise with everything turned off. I then turned things on one by one, noting any changes in the spectrum. For the list noted above, this is the way it looked.

These are a few things contributing to RF noise levels on the MF band.

We have cheap Chinese grow lights to start seedlings for our vegetable garden. We were using these during the daytime hours to augment the low sunlight in early spring. I initially thought this was coming from the solar system. The interference was making a massive noise hump between 750 and 957 KHz. The brand of growlight is BestVA B-1000 LED which was purchased from Amazon.

Next, somewhat surprisingly, the LG computer monitor on my desk was creating a pretty decent rise from 1120 KHz to 1700 KHz. I have three LG computer monitors, this is the newest only this one creates any RF noise.

Then, pretty much every florescent lamp (compact or full-length tube) created a broadband noise increase across the entire MF band and well into HF.

The vacuum cleaner makes a little bit of broadband RF noise when near the receiver. However, you cannot hear the radio when the vacuum is running, so that does not seem to matter.

None of these are surprising. However, I was more surprised that many other electronic devices are not contributing to RF noise in my house.

A little bit about data over power line or power line communications. Searching for power line data can be a bit tricky. First, there is this large voltage 60 Hz (plus harmonics) waveform to deal with. Secondly, there are many different protocols and many different frequencies. I narrowed down my solar system by listening to my Kenwood R-2000 below 300 KHz. Some noise went away when I completely disconnected the inverters. I don’t know the exact frequency, the protocol, the modulation type, etc. But there is something.

Data Over Power line is popular with home automation systems, it can be used to extend Ethernet LAN, and some power companies are using it to control substation equipment, smart power meters, and/or to function as an ISP for their customers. I have heard some HF users complain about BBPL, but I have not experienced it for myself.

The Nautel J-1000

I Finished up this installation of a J-1000 in Brookfield, Connecticut for Nossa Radio. That is a Portuguese broadcaster that owns three other stations in the US.

These Nautels are fairly simple affairs; a controller and two RF amps with incumbent power supplies.

Nautel AM-RF and AC mains surge suppressor

Be sure to install the surge suppressor that comes with the transmitter.

The J-1000 is replacing the 43-year-old Harris MW-1A which will function as a backup. Like all new transmitter installations; some things must be done to complete the job.

Harmonic measurements out to about the 5th or 6th harmonic need to be documented and compliant with NRSC-2 (AM mask requirements). Although NRSC-2 measurements are required, I don’t see how they can enforce that specification after AM HD radio came into being. Nevertheless, it was measured and passed. With the station carrier power of 680 watts, I used the RF monitor port on the back of the transmitter to make the measurement. Otherwise, I would need to find an empty field somewhere 1 KM away and stand in the middle of it to reduce all of the electrical noise.

The NRSC-2 mask is mainly a function of High-Frequency limitation in the audio processor—certain transmitters, like the aforementioned MW1A did make some contributions to out-of-tolerance measurements.

The antenna is a skirted tower that has many other services colocated on it. At the top is WRKI.

Driving away from this site, I would have to agree with the predicted contour map above, at least on the highway. I think it may be a bit different driving around in town.

WKIP; removal of the taller tower

This is the original tower for WKIP, but not the original antenna. It was put up circa 1960 or so and like many towers from that era, has hollow legs. Thus, after 60 years or so, it is deteriorating from the inside out.

This was part of a two-tower directional array. It is odd that a class C station on 1,450 KHz would have a directional antenna at all. Even stranger still, it was directional daytime, non-directional night, both at 1,000 watts. The reason for such an odd situation; the station was co-owned with WGNY in Newburgh and the daytime coverage contours would have overlapped without a directional array. The taller tower is 215 degrees tall with top loading. During the daytime, the pattern goes to the North and it covered very well.

Vertical Bridge, the tower owner, decided it was time to replace the aging structure with a monopole. They are completing the project this summer. Our part is to move WKIP to the shorter tower and put up a temporary FM antenna for the translator. Once the project is completed, WKIP will operate from the shorter tower (which is 85 degrees) permanently, getting rid of the now unnecessary directional antenna on a class C channel. The translator antenna will move back to the monopole, once it is put up.

Problems… Yes, we have a few of those…

First, the short tower had a broken guy wire. Actually, the guy wire was fine, but the lowest grip connecting to the equalizing plate was rusted through. It is fortunate that this was discovered because the upper guy wire was getting ready to let go too. Northeast Towers was able to replace all of the grips on that set of guy wires and re-tension the tower. They did a full investigation of all of the other anchors prior to any climbing. This is in a swamp, which has flooded several times over the last few years.

Tower #2, guy wire repaired, Scala FMVMP translator antenna mounted

Next, the temporary FM translator antenna was hung on the tower. It was thought that the 3/8 sample line from the old AM sample system could be used as a temporary transmission line for this system. Unfortunately, that line turned out to be 75-ohm cable TV drop line and was not suitable for transmission of VHF. We had about 600 feet of leftover 3/8 sample line (Cablewave FCC 38-50J) from a decommissioned AM site, so we used that instead. It has quite a bit of loss on VHF, however, for temporary use, it will work.

Next, it seems this black rat snake had taken up residence in the ATU cabinet. The bottom of the ATU was full of mouse nests going back many years. One of our employees dutifully cleaned out the mouse nests unknowingly under the watchful eyes of this snake. Only after he was done, did he see the snake coiled up on the disused current meter shunt. There was a mild freakout for several minutes, but the snake left on his own and we got back to work. The black rat snakes are helpful to have around, but perhaps best if he stays outside of the ATU. We will seal up the entryway for the coax, which seems to be where all the critters are coming in.

This Kintronic Isocoil was mounted to the back of the ATU with unistrut. Even though this is a temporary installation, I have found that sometimes temporary things can last much longer than anticipated. Besides, it was easier than trying to use pressure treated 4 x 4 lumber.

Next, we measured the ATU with the fancy machine (Agilent E5061B network analyzer). In theory, the ATU input should be 50 ohms to match the incoming transmission line. No, instead it was 38 Ohms -j20.

So, a little bit of a retune was required. With the fancy machine, we were able to get it to 52 ohms -j9 or so. This is good enough for now, there will be numerous cranes in the air and the station has an STA to run at 250 watts for the project’s duration. After the new monopole is up, we will measure the base impedance of the tower and tune up the ATU for 50 ohms and then return the station to full power at 1 KW.

Smaller crane, used to assemble the larger cranes

The old tower coming down:

Top section and top loading wires separated

Two cranes were used; one to hold and lower the tower section, the other to lift two tower workers to cut away the sections. The tower was deemed unsafe to climb, therefore it had to be removed like this. It was also unsafe to drop because of the proximity to the studio building and the other tower, which is being retained.

You get the idea. These tower sections and guy wires were cut up and put in a scrap metal dumpster. They will be recycled into something else.

Now, they will work on removing the old tower base and putting up the monopole. Once that is done, we will tune up the AM on the short tower and get it back to full power.