tech stuff – Page 29 – Engineering Radio

Nanobridge M5 wireless LAN link, Part II

After a bit of delay, we were able to return to the WICC transmitter site to install the Wireless LAN link. The installation was pretty straightforward. The studio unit was mounted on an existing STL tower on the top of the elevator room, the transmitter unit was mounted on an existing pipe on the roof of the transmitter building.

M5 Nanobridge mounted on transmitter building with radome — M5 Nanobridge mounted on transmitter building with RADOME

I included RADOMEs for a couple of reasons; first, there is a lot of critters around of the two-legged and winged kind. The upright two-legged critters may be attracted to the signal-strength lights at night. This unwanted attention could invite the juvenile delinquent’s bored teenagers to throw various objects found laying around on the ground at the antenna, damaging it. The winged type critter may be inclined to view the feed horn as a good nesting location. The other reason is this site gets a lot of rain, wind, ice, and snow, therefore the RADOMEs afford some protection against the weather.

Aiming the antennas was pretty straightforward, but requires at least two people. Using landmarks, we aligned the dishes in the general direction of each other. Both ends of the system were turned on and we had a -89 dBm signal path, and somewhat surprisingly, the radios linked up and my laptop grabbed an IP address via DHCP. Using the signal strength meter on the side of the antenna, each dish was peaked in turn:

M5 Nanobridge Antenna signal strength meter

Then, somebody on either end went below and looked at the signal strength screen on the web interface while the other end peaked. In the end, we had about -65 dBm signal strength, which is somewhat less than the -58 dBm predicted. I think we can do better, so on the next clear day, I am going to peak the signal again.

The data rate initially reported was over 100 MBPS, however, once I started transferring files back and forth, that dropped to about 50 MBPS. If it is raining, that rate drops to about 35 MBPS, which is still far above what we need this link to do. As a test, I streamed a youtube video, downloaded a Windows update, loaded several web pages, and checked my email simultaneously. There were no issues with the data rate while those tasks were being preformed.

It is quite amazing to me that these little inexpensive radios can work so well. My boss thinks that they will be blown up by lightning during the first thunderstorm of the season. I don’t know. There are several of these units have been installed at mountaintop tower sites and have been working for several years without issue.

Next step, installing the IP cameras and warning signs on the fence, setting up the monitoring software, etc.

Cameras mounted on old chimney platform. This is the first set of cameras covering the south, north, and west approaches. A fourth camera will be mounted on the back of the building covering the east approach. Then, under the eves’ cameras will be mounted on all four corners of the building and the generator shed. If anything moves, it will be recorded.

Nautel Radio Coverage Tool

This is a Webinar video from Nautel about their Radio Coverage Tool:

Highlights of the Nautel RF tool kit:

Analyze the proposed transmitter location’s coverage
Tower heights can be adjusted
Antenna gains can be changed
Transmitter power levels
Includes Terrain data
Includes population within coverage areas
Frequency Range 30 Mhz to 3GHz
Useful for general broadcast or point-to-point systems

This can be a useful tool for those looking to gauge the realistic coverage of a station in terrain-challenged areas. It can also be useful for studying STL paths, RPU coverage, etc.

One problem is the power levels and antennas are preset, with the minimum setting of 200 watts into a two-bay antenna. These settings are too high for use when investigating a potential LPFM. For that, Radio Mobile Online (which is the engine behind the Nautel RF tool kit) can be accessed directly via www.ve2dbe.com/rmonline.html. Requires an account, which is very easy to set up. For most users, FM broadcast band frequencies will not be available, however, 2 meter amateur frequencies (146 MHz) are the default, and for all practical purposes, will model coverage in the FM band (88 to 108 MHz) just fine.

By creating a hypothetical LP100 transmitter site, the coverages between the FCC 60 dBu contour and the actual coverage based on terrain can be compared. This is the FCC 60 dBu coverage contour:

Example contour, LP-100 station — Example 60 dBu contour, LP-100 station

According to the US Census data, this station has a population coverage of; 30,721 in the 70 dBu or 3.162 mV/m contour, 92,574 in the 60 dBu or 1 mV/m contour, and 165,183 in the 50 dBu or 0.316 mV/m contour. Courtesy of REC Network. The 60 dBu contour is considered the protected area licensed for use by the FCC.

Looking at a coverage terrain map, the picture changes somewhat:

This is based on predicted receiver location using terrain data; receiver antenna height 1 meter, 90% reliability, minimum signal level 10 µV (20 dBu, yellow, very good car radios) and 31.62 µV (30 dBu, green, good radios and indoor reception). Areas to the south and east of the transmitter are shaded by a large hill, thus they show low or no signal on the terrain based coverage map. UN Population data indicates the yellow has 178,573 and the green area has 72,014 persons. This map does not take into account co-channel and adjacent channel interference, which there is sure to be.

When comparing the two maps, one can see the coverage holes in the terrain map that are within the 60 dBu contour. There may also be a slight difference in populations covered because the FCC map uses 2010 US Census data and the Radio Mobile Map uses UN population data. For general planning purposes, the area shaded in green would be a safe bet on good reception, all other things being equal.

Since the LPFM stations are very limited in their ERP, finding a good transmitter site that will cover the desired area will be key to a successful operation.

Zonecasting; the Technical Details

I saw this item many weeks ago, but, had not had time to look at it until now. Geo Broadcasting Solutions has filed Petition for Rule Making (RM-11659) based on a system that divides the coverage area of major stations into smaller zones allowing for ad targeting of specific audiences. They have coined the term “Zone Casting” to describe the scheme. It is covered by two US-issued patents filed by Lazer Spots, LLC: 20120014370 and 20110065377. After a look at these two patents, it seems there are three possible ways to accomplish this Zone Casting Scheme:

In the first described method, the main transmitter is broadcasting area wide and all the zone transmitters are muted. An inaudible signal is transmitted to all units, the main transmitter is then muted and the zone transmitters turn on and transmit localized content. After the local information is transmitted, the zone transmitters mute and the main transmitter resumes broadcasting.
In the second described method, the main transmitter and the zone transmitters are broadcasting area-wide information. The main transmitter ceases broadcasting area-wide information and the zone transmitters begin broadcasting localized information. At the end of the localized information, the main transmitter and zone transmitters transmit area-wide information.
In the third describe method, the main transmitter and zone transmitters are broadcasting wide area information with “capture ratio pattern.” The main transmitter initiates an alteration, temporarily becoming a zone transmitter. The zone transmitters then transmit localized content. After the localized content, the main transmitter becomes a main transmitter again.

All of the transmitters are linked to the studio via digital STL systems, and content for the zone transmitters is distributed via IP network. The transmitter frequencies are synced with GPS, similar to FM on channel booster stations. Method number three includes possibly switching the transmitter output to a lower gain and or lower height antenna.

Of the three methods, the first system will result in the fewest interference issues. No matter which method is used, there will be interference issues between the zone transmitters and or the main transmitter where the signal strengths are equal and the audio is 180 degrees out of phase. These can be moved around slightly by adding delay to the audio signal, but they will always be present. More about Same Frequency Networks (SFN) and Synchronized FM signals can be found here. While the zone transmitters are transmitting dissimilar localized information, standard capture effect rules apply.

The system has had limited testing in Salt Lake City, Utah (KDUT) and Avon Park, Florida (WWOJ), which according to the filing and comments, went well.

Geo-Broadcasting is applying to conduct a full test with WRMF in Palm Beach, FL. The expected installation will include up to 22 zone transmitters.

Conceptually, tightly targeted advertising is not a bad idea. Advertisers like it because they perceive a better return for their dollar. The cost of such a system is not insignificant. Transmitter site leases run $1-2K per month, leased data lines, equipment, installation work, equipment shelters, etc will likely run several hundred thousand dollars or more.

If it gets approved by the FCC, it will be interesting to see how it works and whether or not the system is financially justifiable.

The Nautel NV-5 Transmitter

We are currently installing this sweet little transmitter:

Like its big brother, the NV-40 at WVPS, the NV-5 is a very cool transmitter. I am a born skeptic, things like touchscreen displays tend to make me a little nervous, especially on a transmitter connected to a 350 feet tall steel tower right next to the transmitter building. That is the one major difference between WVPS and this site; at Mount Mansfield there are many things between the transmitter and antenna, but in this place, not so much. Even so, Nautel makes a good product, so troubles are not expected.

The ground strap, AC power, remote control, and composite audio connections were all made without difficulty. The result, new transmitter on the air:

This unit is analog only, but the information on the spectral display is still useful. The GUI uses Linux with a touch screen, which is a neat feature.

Nautel NV-5 FM transmitter controller board

In case the front panel GUI goes out, all transmitter controls can be accessed via push buttons on the remote control interface, which is the small board to the right. The main controller board is on the left.