Dear BPR Tech,
Why can I not receive BPR News on 107.9 in Fairview but a station out of Charlotte comes in clearly?
We’ve received quite a few similar questions from listeners in the Fairview area. The answer is a bit complicated and has several key factors that come into play. I hope to outline these and give you a better understanding of the challenges we face across our broadcast area.
First let’s look at where our transmitter for 107.9 is located and its designated coverage area. The broadcast antenna is located on top of the Vanderbilt apartments, not far from our studios, at approximately 128ft above ground level.
When the FCC grants a station a license for a transmitter, one of the parameters it states is the maximum radiated power that the antenna can emit. In our case, 243 watts for 107.9. Stations are also given a service contour which shows the approximate coverage area. Below is the service contour in blue for BPR News on 107.9. That transmitters ID to the FCC is W300CR, as shown on the map. The line is called the 60 dBu Service Contour.
I want to stress the approximate aspect of this map. These contours are generated by the FCC using the height of the antenna above an average ground level, the pattern of the antenna (directional or non-directional), the radiated power from the antenna, and most importantly, are calculated as flat terrain. When comparing real world coverage to the service contour, there are typically vast differences. The two may be quite similar in very flat areas, such as the Midwest. Or they might look nothing alike in mountainous areas, like what we have in much of our broadcast area.
Out of many factors that come into play when discussing reception, terrain is one of the most important. While FM broadcast signals are not strictly limited by line-of-sight, it’s not too far from their real-world behavior. Let’s take a look at what the terrain between our 107.9 transmitter and Fairview is like:
To the left is 107.9, to the right is Fairview. Even with all the terrain changes between the two points, both ends are just about the same altitude. This terrain profile shows us the two major blocks that reduce our signal towards Fairview. The first peak is the ridge between downtown Asheville and Haw Creek, the second much larger set of peaks is Minehole Gap on 74.
The effects of terrain on reception can be better approximated using different modeling techniques. One of these is the Longley-Rice model. This model takes into account the local topography in addition to the other data used by the FCC. It provides a shaded overlay which can better represent areas of good reception (blue) and fringe reception (red). Here you can see how terrain casts “shadows” on the backside of higher elevations.
You can also see how some areas outside of the 60 dBu contour have good reception, and some places within have poor to no reception. Do you see that blue patch to the south-east along 74? That is the transmitter side of Minehole Gap. Once you crest that rise, signal drops dramatically.
Ok, so that’s why I can’t pick up BPR News in Fairview. But why can I pick up a station out of Charlotte so clearly?
This is due to the most important factor in good coverage: power. You are hearing WLNK, whose transmitter is located just north of Gastonia. They are broadcasting at 100,000 watts, from a 1600 ft tower. That’s more than 400 times our power. In concert with their high power, their height plays a huge role in their reception this far west.
WLNKs antenna is located at 2503 ft above sea level, while our antenna on top of the Vanderbilt is 2316 ft. Even with us being in the mountains, their antenna is still 187 ft above ours!
Another reason your car radio in particular might suddenly lock on to their signal is that they are broadcasting an HD signal. Contrary to the common meaning of that abbreviation, HD in this case does not mean High Definition, it means Hybrid Digital. That means they are broadcasting a traditional analog signal that all FM radios can pick up, but in addition to that they are broadcasting a digital subchannel that can have better audio quality if set up to do so. If your car radio has HD capability, and if it detects a strong enough signal it will lock on.
Why can’t you just turn the power up or put the antenna in another place?
Our output power is dictated by the FCC. Exceeding that could lead to interference with other stations and result in hefty fines from the FCC.
Antenna placement is a tricky one. Not every tower or building you see is an option. The process of mounting an antenna on a tower typically starts with finding a tower owner that will lease you space on their tower. This also involves having engineering studies done to ensure the tower can take the weight and support the wind load of the additional equipment. The lease alone can be prohibitively expensive. Mounting an antenna on a building involves similar steps and usually requires the construction of a dedicated support structure for the antenna.
Not all tower owners want to have an FM station on their tower, as they require more space than other tenants like cell providers or commercial two-way radio services. That is usually reflected in the cost of the lease.
Building a brand-new tower is a last option but likely the most expensive. On top of the fact that most of the ideal broadcast points around Asheville already have towers, it involves buying the land that the tower will occupy. To go along with that, if there is not an existing road to the site one will have to be built, and at the minimum electrical service will have to be run there. Even a light duty tower can cost upwards of $10,000, with heavier duty and taller towers easily reaching tens or hundreds of thousands of dollars. Add construction costs for the tower, large concrete base, and building to house the transmitter and other equipment, you can see how that can skyrocket in price.
What if I can pick up BPR News on 107.9 from home but it’s staticky? How can I improve that?
I suggest you look at our Improve Reception page.