Engineering Radio – Page 131 – One Hundred percent Human Generated Content for your Reading Enjoyment

FCC seeks further comment on Low Power FM (LPFM)

While I was away, the FCC released a Further Notice of Proposed Rule Making (11-105) regarding LPFM and translators. There are several issues with a backlog of translator applications and the possible LPFM window that looms out in the future somewhere. The current FCC translator rules bear little or no resemblance to the reality of FM translator use today.

The basic translator rules are found in FCC 74.1206 through 74.1290 with the programming and permissible service outlined in FCC 74.1231:

Sec. 74.1231 Purpose and permissible service.

(a) FM translators provide a means whereby the signals of AM or FM broadcast stations may be retransmitted to areas in which direct reception of such AM or FM broadcast stations is unsatisfactory due to distance or intervening terrain barriers, and a means for AM Class D stations to continue operating at night.
(b) An FM translator may be used for the purpose of retransmitting the signals of a primary AM or FM radio broadcast station or another translator station the signal of which is received directly through space, converted, and suitably amplified, and originating programming to the extent authorized in paragraphs (f), (g), and (h) of this section. However, an FM translator providing fill-in service may use any terrestrial facilities to receive the signal that is being rebroadcast. An FM booster station or a noncommercial educational FM translator station that is operating on a reserved channel (Channels 201-220) and is owned and operated by the licensee of the primary noncommercial educational station it rebroadcasts may use alternative signal delivery means, including, but not limited to, satellite and terrestrial microwave facilities. Provided, however, that an applicant for a noncommercial educational translator operating on a reserved channel (Channel 201-220) and owned and operated by the licensee of the primary noncommercial educational AM or FM station it rebroadcasts complies with either paragraph (b)(1) or (b)(2) of this section:
(1) The applicant demonstrates that:
(i) The transmitter site of the proposed FM translator station is within 80 kilometers of the predicted 1 mV/m contour of the primary station to be rebroadcast; or,
(ii) The transmitter site of the proposed FM translator station is more than 160 kilometers from the transmitter site of any authorized full service noncommercial educational FM station; or,
(iii) The application is mutually exclusive with an application containing the showing as required by paragraph 74.1231(b)(2) (i) or (ii) of this section; or,
(iv) The application is filed after October 1, 1992.
(2) If the transmitter site of the proposed FM translator station is more than 80 kilometers from the predicted 1 mV/m contour of the primary station to be rebroadcast or is within 160 kilometers of the transmitter site of any authorized full service noncommercial educational FM station, the applicant must show that:
(i) An alternative frequency can be used at the same site as the proposed FM translator’s transmitter location and can provide signal coverage to the same area encompassed by the applicant’s proposed 1 mV/m contour; or,
(ii) An alternative frequency can be used at a different site and can provide signal coverage to the same area encompassed by the applicant’s proposed 1 mV/m contour.
(c) The transmissions of each FM translator or booster station shall be intended only for direct reception by the general public. An FM translator or booster shall not be operated solely for the purpose of relaying signals to one or more fixed received points for retransmission, distribution, or further relaying in order to establish a point-to-point FM radio relay system.
(d) The technical characteristics of the retransmitted signals shall not be deliberately altered so as to hinder reception on conventional FM broadcast receivers.
(e) An FM translator shall not deliberately retransmit the signals of any station other than the station it is authorized to retransmit. Precautions shall be taken to avoid unintentional retransmission of such other signals.
(f) A locally generated radio frequency signal similar to that of an FM broadcast station and modulated with aural information may be connected to the input terminals of an FM translator for the purpose of transmitting voice announcements. The radio frequency signals shall be on the same channel as the normally used off-the-air signal being rebroadcast. Connection of the locally generated signals shall be made by any automatic means when transmitting originations concerning
financial support. The connections for emergency transmissions may be made manually. The apparatus used to generate the local signal that is used to modulate the FM translator must be capable of producing an aural signal which will provide acceptable reception on FM receivers designed for the transmission standards employed by FM broadcast stations.
(g) The aural material transmitted as permitted in paragraph (f) of this section shall be limited to emergency warnings of imminent danger and to seeking or acknowledging financial support deemed necessary to the continued operation of the translator. Originations concerning financial support are limited to a total of 30 seconds an hour. Within this limitation the length of any particular announcement will be left to the discretion of the translator station licensee. Solicitations of contributions shall be limited to the defrayal of the costs of installation, operation and maintenance of the translator or acknowledgements of financial support for those purposes. Such acknowledgements may include identification of the contributors, the size or nature of the contributions and advertising messages of contributors. Emergency transmissions shall be no longer or more frequent than necessary to protect life and property.
(h) An FM translator station that rebroadcasts a Class D AM radio broadcast station as its primary station may originate programming during the hours the primary station is not operating, subject to the provisions of Sec. 74.1263(b) of this part.
(i) FM broadcast booster stations provide a means whereby the licensee of an FM broadcast station may provide service to areas in any region within the primary station’s predicted, authorized service contours. An FM broadcast booster station is authorized to retransmit only the signals of its primary station which have been received directly through space and suitably amplified, or received by alternative signal delivery means including, but not limited to, satellite and terrestrial microwave facilities. The FM booster station shall not retransmit the signals of any other station nor make independent transmissions, except that locally generated signals may be used to excite the booster apparatus for the purpose of conducting tests and measurements essential to the proper installation and maintenance of the apparatus.

With a possible exception for use by Class D AM stations, the translator service has gone far away from what it was intended to be and even, in some cases, contradicts the current rules. DIY Media goes more into this in Unholy Alliance.

Consolidators are using translators to get around market ownership caps by using them to re-broadcast HD-2 and HD-3 channels, which would otherwise go unheard. Others are using translators to establish large networks of over-the-air relays to greatly extend their coverage far beyond any natural signal contour. Religious and public radio stations rely extensively on translators to establish radio signals that are several times the size of the original station. In one case, a translator in Harrisburg, PA is broadcasting a satellite feed of the True Oldies Channel that does not appear on any AM, FM or HD sub-channel in the market. The 80/160 KM distances noted above in section B(1)(i) and (ii) seem to be largely ignored.

What the FCC wants to know is this: There are thousands of pending translator applications; what is to be done about them in light of the new LPFM legislation Congress passed last year? Should they be dismissed, approved, or some market-based combination of the two? Keep in mind, the new LPFM stations are on an equal regulatory footing with translators, unlike full-power FM or the previous LPFM licenses granted in 2003.

Whatever the outcome, it would appear that this will be the final chance to get an LPFM license when the filing window opens. After this, there will likely not be a scrap of spectrum left to dole out. The deadline for filing comments with the FCC is August 29th.

Mount Mansfield, highest point in Vermont

As alluded to in the previous post, I spent a fair amount of time at Mt. Mansfield last month. It is the highest point in the state of Vermont, topping out at 4,393 feet (1,339 M). At the top, there is a large transmission facility that is home to WCAX-TV, WPTZ-TV, WVPS, WEZF, several low-power TVs, NOAA weather radio, etc. Next door, Vermont Public TV is housed in a separate building. Here are a few pictures and descriptions. First of all, Mount Mansfield is the home of the Stowe Ski area. They own the access road to the top of the mountain and are quite proud of it. In the summertime, the toll for a carload of people is $26.00.

The transmitter building is below the actual peak. This is one of the few transmitter sites that is manned 24/7, as such there is a working kitchen, bathroom, bunk rooms, and so on. I’d imagine it gets pretty deary up there in the wintertime, but perhaps not.

The transmitters are located along a long hallway. WEZF and WVPS share a room, and WCAX and WPTZ are in open bays as are the low-power TVs. NOAA weather radio and some other government transmitters are located in the garage.

All of the TV transmitters are new because of the recent conversion from analog to digital transmission. WCAX is noted as channel three, which was their analog channel, they actually transmit on channel 22 with a power of 443 KW ERP.

Like WCAX, WPTZ was on channel five, it is now transmitting on channel 14 with 650 KW ERP.

The site is backed up by two 1.2 MW diesel generators, which can be paralleled with the commercial power grid, if needed, during peak demand times. These generators also provide backup power for the Stowe Ski area. There is a 50 KW back up back up generator that runs all of the emergency transmitter cooling equipment if the two main backup generators fail.

All of this generating equipment requires a lot of fuel.

Transmitter building and fuel storage tanks

The TV and FM broadcast antennas are located just below the peak

I don’t recall which TV station belongs to which antenna. The FMs are combined into the four-bay, three-around panel antenna, this includes WVPS’s HD radio signal.

Mount Mansfield from the top looking west

From the very top looking west into the aperture of the TV antennas. I only stood there for as long as it took to get a good picture, then departed. Off to the left of this view is the antenna for Vermont Public TV.

Mount Mansfield Vermont Public TV antenna

The transmission lines go down the hill on a large ice bridge. An absolute necessity as the rime ice can sometimes accumulate several inches.

Tower base, is the location of the highest RF concentration, according to the TV engineers. I only lingered here to snap a few quick photos.

All of the STL antennas are mounted to the side of the transmitter building next to the living quarters.

On top of all that, as if that weren’t enough, there is the view. I would also comment a bit on the weather. In some cases, the site can be completely engulfed in a grey dull fog bank one minute, then the wind changes direction, the sun comes out and you see this:

I can think of worse things.

I regret that I didn’t have a better camera with me as several of the pertinent pictures came out blurry. All of these pictures were taken with my cellphone camera, which works well when it works. It is also very convenient because it is almost always with me and I don’t have to remember to bring another gadget. However, it this is going to be a semi-serious endeavor, I will have to take some of my earnings from these scribblings and buy a good camera.

New Nautel NV-40 at WVPS, Burlington, VT

Sorry for the prolonged absence. I have been, quite literally, out of reach for the last two weeks. In fact, for the entire month of July, I spent just five days at home. Some of the travel was for work and some for pleasure.

On the work side of the equation, WVPS in Burlington, Vermont has a new Nautel NV-40 transmitter. WVPS is the NPR affiliate for Vermont Public Radio and it’s transmitter site is located on top of Mt. Mansfield, in Stowe, VT. I will do a separate article about the Mt. Mansfield transmitter site because it is an interesting place. WVPS is a Class C FM on 107.9 Mhz. They have one HD subchannel for the VPR classical music format.

The Nautel NV-40 transmitter is greatly updated from the V-40, which was installed at WHUD. Basically, the V-40 is four ten-kilowatt transmitters combined. It is a novel approach and offers quite a bit of redundancy as entire transmitters can be switched off and worked on with the other three remaining on the air at full power.

The NV-40 is a single large chassis with internal combining networks. It uses different RF modules but the same power supplies. The entire thing is controlled by a fancy GUI on the front of the transmitter but also has the ability for manual control if the GUI fails. That is a key feature not seen in other transmitters which simply won’t work without the fancy computer. Other things that I like, are the ability to control all of the biasing and other options via the GUI and things like a spectrum analyzer and Lissajous display. The ability to look at several graphic displays at once makes it easy to configure and monitor.

The transmitter arrived at the top of the mountain via a local moving company. After unloading it on the loading dock, it took some amount of doing to get it down the hall into the transmitter room. The thing weighs in at 1,600 pounds after being uncrated.

Nautel NV-40, Mt. Manchester transmitter site loading dock — Nautel NV-40, Mt. Mansfield transmitter site loading dock

Unpacked:

Nautel NV-40 uncrated and read to move down the hallway

Moving into the final position in the WVPS transmitter room.

Movers putting transmitter into final location and removing pallet jack

The connections were made to the transmitter, including connecting grounding strap to the back, 200 amp electrical service and the RF output connection via 3 inch rigid coax.

The remote control consists of basic transmitter functions going to a dial up Gentner remote control and a Network connection going to the GUI. The network connection allows persons on the network to use a web browser to look at the GUI. The HD radio connections are made via a HD radio importer and exporter, located at the studio, which also uses the network, via a connection on the exciters, to send the HD subchannel. The analog main channel is via an AES/EBU connection from the STL.

All connections go through large toroids to help isolate the transmitter from any lightning-related surges.

Before I left, we tested it at full TPO into the dummy load. All worked well, the only outstanding issue was getting the HD radio importer/exporters to work over the network, which was out of my jurisdiction.

Here is a rather blurry picture of your author standing next to the NV-40 with the exciter and GUI turned on. There are to IEC power connectors at the top of the transmitter that go to the GUI and exciters. This allows those part of the transmitter to run on UPS’s, which is nice, being that the GUI takes about a minute to boot up after power failure.

What is “Phasing” as it relates to radio?

Occasional reader Jeffery asks a good question, which I will attempt to answer here in simple terms. Phasing, when used with antennas, refers to the relationship that two or more radiating elements share with the waveform being transmitted. It is used to create an RF radiation pattern by adding energy to the wavefront in one direction by taking energy away from the wavefront in another direction.

Phasing is often described as +/- X number of degrees from a reference point. Graphically, it would look like this:

One wavelength with +/- 180 degrees notated

The reference point can be changed to any point on the waveform, in radio applications it is usually oriented around +/- 180 degrees. If the reference point is a single tower or element then this would be the end of the story. Add a second tower to this system and it would look something like this:

In this picture we have two waves being radiated from two separate elements. These elements are spaced 100 degrees apart and tower #2 is phased to +90 degrees. RF generator is coupled to both towers via a power divider, the reference tower (tower #1) is feed with 57% of the power that tower #2 is being feed. Thus, the ratio of power to the respective towers would be 57:42. Thus, if tower one had a power reading of 1.00, tower two would be 0.74. The towers are on a north/south line with the reference tower bearing 180° from tower #2. In the area of subtraction, the waveforms from each tower cancel each other out to some radiating less power toward the south; in the area of addition, the waveforms sum to create a more powerful waveform, radiating more power towards the north.

Resulting pattern (WKIP, Poughkeepsie, NY):

This is a typical two tower array, however, there are two slight differences; the reference tower is 215 degrees tall, tower two is 90 degrees tall. This is yet another use of “degrees” to relate electrical length or separations. The second, more notable distinction is that this array is Directional daytime, and non-directional night time, which is the opposite of most AM stations in this country.

Electrical height can also be described as a function of wave length, e.g. 1/4 wave, 1/2 wave, etc. Most AM towers in this country are 1/4 wave length, which equates to 90 degrees. Often, higher powered stations, and some low powered stations put up towers near 1/2 wavelength due to the better ground wave performance of those towers. At lower dial positions, a 1/2 wave tower becomes an expensive proposition due to the height required.

In theory, an unlimited number of towers can be used to create a pattern by introducing nulls (areas of subtraction) and lobes (areas of addition). In practice, the highest number of towers I’ve ever heard being used in an AM directional array is twelve; KFXR 1190, Dallas, TX. There may be others, too.

An excellent resource for AM directional antenna technical information is Jack Layton’s Directional Antennas Made Simple, which is out of print but available from various sources.