Paul Thurst – Page 162 – Engineering Radio

Digital Radio Mondiale, an alternative to HD radio?

Could be. Digital Radio Mondiale, or DRM, is a modulation scheme that a group of broadcasters and transmitter manufacturers have been working on since about 1997 or so. There are numerous shortwave broadcasters; the BBC, the CBC, Deutsche Welle, Radio France Internationale, the VOA, and others have been using DRM on shortwave for several years now. I can state that the shortwave DRM system works well, I have a software decoder and use the sound card input on my computer to decode and listen to DRM shortwave broadcasts.

The goal of DRM is to establish a worldwide open standard for digital broadcasting in the LF, MF, HF, and VHF bands. In the early years of development, DRM was designed for digital broadcasting on bands below 30 MHz. This system is now known as DRM30. Since then, the DRM consortium has expanded that to the VHF band (up to 174 MHz) as well (meaning where the current FM band is located) and has called that system DRM+.

DRM uses COFDM (Coded Orthogonal Frequency Division Multiplex) modulation, which is the same as IBOC HD radio^TM. This is a robust modulation system that employs multiple carriers at lower power (than an analog carrier) spread across the entire allotted bandwidth.

One of the claims is DRM transmits less power and is more energy efficient. In general, digital radio modulation does transmit less power, that is true. However, transmitters have to be run more linearly for digital due to the increased bandwidth. This may not translate to greatly increased efficiency from the AC mains to RF standpoint. Because of that, there is more waste heat, and thus more air conditioning is needed to cool the transmitter room.

Some of the advantages of DRM over Ibiquity’s HD radio^TM are:

Open source system. Royalties are paid by the transmitter manufacturers only (and to date, most major US transmitter manufacturers have already paid these). There is no royalties paid by the broadcaster to install DRM or by the consumer when purchasing a DRM-capable receiver. One company does not own the rights to the modulation system for all the broadcasters in the country.
Universally standard; accepted by the European Telecommunications Standards Institute (ETSI), International Electrotechnical Committee (IEC), and the International Telecommunications Union (ITU).
The CODEC is HE-AAC 4, which is widely used worldwide.
DRM30 and DRM+ fit into existing band plans and will not interfere with other users on adjacent channels. DRM30 is designed for 9 KHz channel spacing and DRM+ is designed for 100 kHz channel spacing, all of which comply with existing FCC regulations.
Standardized receiver profiles are things that must be included in all DRM receivers. There are several advanced options as well, such as a media-rich system that includes video.
DRM+ has several added features: DRM text, which is similar to RBDS. EPG or electronic programming guide, which shows what is coming up next and a searchable schedule of when programs may be heard out to seven days. Some DRM+ receivers will have a TIVO-like recording device that allows the user to record programs and playback later.
Traffic reporting and routing

In addition to that, DRM30 stations have the ability to transmit low frame rate H. 264 video. This is a distinct advantage for short-wave stations that are seeking a way around firewall blocking. The video image is small, 176 x 144 pixels and it is 8 frames per second, which is about as good as can be expected using a 9 KHz channel.

In some cases, DRM is capable of a hybrid mode (ed note: DRM calls this “Simulcast mode”), but what have we learned about hybrid mode digital radio: It doesn’t work very well. In short, it would be better if DRM were employed in the digital-only mode. To many, this is a distinct disadvantage, but I don’t see it that way. There have been many that have made the IBOC rollout/FM broadcasting rollout analogy. Frankly, those arguments don’t hold water. When FM was introduced, no attempt was made to shoehorn it into the existing AM (Standard Broadcast) band, it was not designed to interfere with other stations or itself, power levels were sufficient for good reception using existing technology, quality over AM was markedly improved and programming was often separate (simulcasting with existing AMs did not start until later). My point here is that any digital broadcasting should be introduced on a separate set of frequencies. Some have proposed using TV channels 5 and 6, which makes some good sense. Whatever the outcome is, we have learned, the hard and expensive way, that hybrid digital broadcasting does not work well.

A brief video about DRM30.

Currently, DRM30 is only allowed on shortwave broadcast frequencies in the US. I asked a product development engineer from a major reputable broadcast transmitter manufacturer about this, and his response was:

Medium-wave broadcasting in the US already has HD radio, so the FCC would be disinclined to allow a new standard
One might be able to apply for an experimental license to broadcast DRM, but it would likely have an expiration date
It is possible to operate DRM in a hybrid mode on the AM band and occupy the same bandwidth as HD radio^TM (30 kHz), it might also be possible to squeeze that down to 20 KHz.
Most modern (read: solid-state) AM broadcast transmitters should be able to transmit DRM without modification (antenna systems may be a different matter).

It might be fun to apply for an experimental license to broadcast somewhere in the 1600-1700 KHz range with DRM30 only and no analog modulation, except for an hourly station ID in Morse. A 1/4-wave tower in the middle of that band would be 141 feet tall. With the use of a skirt, a grounded tower can be employed. That and a few above-ground radials and the system would likely be pretty efficient. Part of the experiment would include driving around and taking signal strength readings while recording the programming material. This would give some real-world testing on how the system would perform in widespread use.

Of course, this would require a major about-face by the FCC, which is not likely unless someone there grows or somehow acquires a backbone.

Some people question the need to do any type of digital broadcasting. I am a realist, in one way, shape, or form, digital radio broadcasting will (or already is) take(ing) place. It would make the most sense if the best system were used, which is not necessarily the first system proposed. The big question is, will today’s terrestrial broadcasters be involved, or out of business?

Things that make you go, Hmmm.

I was doing a weekly visit to one of our FM transmitter sites the other day when I noticed this:

Dented deadbolt lock at transmitter site — Dented deadbolt lock at the transmitter site

Looks like somebody has been whacking the deadbolt lock with a hammer or a wrench or something. Pretty sure that was not like that the last time I was here. Time to get one of those IP cameras and set it up on the tower.

Tower Safety Equipment

The tower climbing video that has gone nearly viral pointed out a few things. Climbing towers is a dangerous business, best left to those who are trained for it and have the insurance.

It is true that tower climbing contractors have the responsibility to protect their own workers while working on a client’s tower. That does not completely absolve the tower owner from liability. It is incumbent on the tower owner to provide a safe structure to climb. This can mean the mechanical integrity of the tower, reduction of transmitter power while workers are in high RF energy fields, and providing the proper permanently attached safety equipment on the tower itself; Climbing ladders, ladder safety cages, rungs, elevators, and fall arresting gear.

In that tower video post, I mentioned something called a safety climb. That is a cable, usually 3/8 inch stainless steel aircraft cable, attached, about eight inches from the climbing surface like this:

Western Electric 200 foot tower with retro fitted safety climb — [

The tower itself was built in 1959 and did not have this equipment when new. This was a retro fit kit, installed in 2003, I believe.

The tower climber wears a harness with a special karabiner attached to the front and waist level. When climbing this ladder, the karabiner slides up the cable. If he were to fall, the karabiner has an auto-locking or braking mechanism that would stop his fall.

Tower safety climb, attached to climbing ladder

Many tower climbers, especially those that have been in the business for a while, do not like these things. When climbing, especially if one has long legs, the tendency is to bump your knees on the bottom of the next ladder rung. This is because the belt holds the climber’s waist making it difficult to get the rear end out, away from the ladder the way most people like to climb. The alternative is to climb with the knees spread apart, like a frog, which is hard on the hamstrings and quite literally, a pain in the ass. However, if a tower is so equipped, it must be used.

I have, wherever possible, retrofitted towers with these devices. Of course, all new towers come equipped with them. In some situations, it is not possible to retrofit towers with safety climbs, either because there is no attachment point at the top of the tower that meets the OHSA spec, there is not a climbing ladder, or it would affect the tower tuning, as in an AM tower or near a TV or FM antenna.

Hundreds of gallons of ink have been spilled by Los Federals in OHSA regulations 29 CFR 1926 and 29 CFR 1910.268(g) regarding fall protection and fall protection equipment for telecommunications workers. In this litigious world, we live in, tower owners and or their on-site representatives should know these rules and make sure they are followed.

Where the rubber meets the road

This is the quandary that I have been in these last few months: Time, as they say, is money. The end product might not seem like it, however, this blog takes up a goodly amount of time. There is the writing, research, taking pictures, editing, and whatnot. Then there is back-end stuff, updating software, plugins, etc.

Then there is actual money expended: domain registration and website hosting.

In short, it is not free, at least not for me anyway.

I did place a few Google Ads in line with some of the content to offset the money part, which they have met that goal, but not much else.

While it is nice to have a hobby, and fun to tell stories about radio engineering, in the end, it really does not help me earn more money, support my family, advance my carrier, or my standing in the community. The children are young, but that will not stay that way for long. Before I know it there will be braces to pay for, a car or two, a college education, and whatever comes after that. Not to mention my own superannuation to look forward to, with such considerations as adding to the retirement account.

There is another shift in my status coming up, with my wife off to work again as a school teacher. I find there are not enough hours in the day to work the part-time radio engineering gig and meet the school bus to offload the children. Therefore, something has to give, that being the part-time radio engineering gig.

I am, therefore, looking for ways to make money at home. Developing this blog or turning it into a full-fledged radio engineering news website might be fun, but it would be much more work, and there is the rub. I can’t do more work on this site without seeing some return. I don’t mind working, in fact, I enjoy working, but I can’t do it for free.

So, I am open to ideas on how to monetize this blog or develop it into something else that will make some money. The third option is to let it go… I’d rather not do that.