General – Engineering Radio

Hurricanes

I have been reading about WWNC Asheville, North Carolina in the aftermath of Hurricane Helene. That is an AM station on 570 KHz (5 KW DA-N) owned by iHeart Media. They have been simulcasting on all of the local iHeart signals in the area and according to WRAL-TV, have been the only source of information for people who have been cut off in the mountainous areas.

While the power is out, wired telephone service is down, cellphones and mobile data are unavailable, AM radio still gets through. Yes, FEMA has satellite phones and can work with commercial wireless providers to re-establish wireless networks and connectivity. However, it often takes them days to react and weeks to get on site.

Stations like WWNC that stay on the air during disasters are vital resources to their communities. The fact that they remain on the air requires planning and forethought. Emergency power at both the transmitter and studio is the most important and most expensive thing. After that, backup programming feeds and sources, secure shelters for personnel, food, water, and even spare clothing. Having experienced several of these events; Bill Ruck in his Radio World letter said it best, Engineers need to take care of themselves.

That means not taking excessive risks during the event, eating properly, and getting adequate sleep. Lack of sleep can lead to poor decision-making processes, making matters worse.

Sometimes transmitter sites are inaccessible or completely destroyed. Having a plan ahead of time to get some signal on the air is always a good idea. Sometimes an area is so severely impacted that there is no normalcy. Things that we take for granted are simply gone. I found the best way to deal with this is to take a step back, take stock of the situation, if you can find others who are working on disaster relief, coordinate with them, come up with a plan, then proceed carefully and be ready to adapt as the situation requires.

The next Hurricane; Milton, is taking a line towards Florida.

The Hurricane Watch Network will be active tonight at 14.325 or 7.268 MHz starting at 5 PM EDT for Amateur Radio operations and Shortwave Listeners.

WX4NHC is the Amateur Radio station for the Hurricane Warning Center. They have useful information preparedness, information gathering, and post-disaster response.

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.

Generator Replacement

This Onan 30OEK propane-powered generator has been in service for 39 years at a transmitter site where the power goes out often. It has a lot of hours on it. The hour meter stopped working about 15 years ago, but the hours back then were 1097.

In addition, the main shaft seal started leaking oil about 10 years ago, creating an oily blowback mess every time the generator ran for more than a few hours. The block heater went bad, the battery charger overcharged then exploded the battery splashing sulfuric acid all over the housing and engine block.

The last power outage was the final one. It ran for a few hours then faulted. When the local engineer tried to restart it, it was never able to get to speed and was misfiring badly. Below appeared a large and spreading puddle of engine oil.

As this station is one of the major money makers for the owner, a replacement generator was obtained.

Cummins RS50 50 KW Propane powered generator

This is larger than the old generator. The good news; now the AC can be put on the generator to keep the room cool. In the past, the backup cooling fan was used when on generator power, which sucked dirt, bugs, and pollen into the room.

It will also have considerable headroom for any additional loads that may be installed in the future.

We had to enlarge the opening for the radiator and put in some steel angle for the lintels.

Exhaust piped outside with the radiator air

The first start run and load test went well. I ran it for about 30 minutes under full load, enough time to burn the paint off the exhaust manifold. Seems like a pretty solid unit. With the power conditions at this site, it will get a lot of use.

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.