What is the Coverage of a Community Radio Station with 25 to 100 Watts and a 30-Meter Tower?

Ricardo Gurgel
10 de ago.
6 min de leitura

It’s not hard to find FM stations with 10,000 watts of power in capital cities or large inland towns. However, the fact that a commercial FM operates at a power level 400 times greater than that of a community radio station (Radcom) does not mean it will have 400 times the coverage. A small community FM operating at 87.9 MHz with 25 watts of power can, under certain conditions, surprise you with its reach.

A more realistic—though still incomplete—rule of thumb is that to double the range, you need to quadruple the power. This logic has its limits because there are other important variables in this equation, such as the curvature of the Earth and the accumulation of physical barriers as distance increases.

For the sake of understanding, let’s run a simple comparison:

Straight to the point: going from 25 W to 100 W (×4 in power) will not quadruple the coverage.
In terrestrial radio, the coverage radius increases more slowly, approximately as:
range ∝ (power)^(1/n), with n between 2 and 4(n=2 in free space; n=3–4 in real areas with terrain/buildings)

So, from 25 W → 100 W (factor of 4):
- Optimistic scenario (n=2): radius ≈ 2×
- Typical (n≈3): radius ≈ 1.6×
- Difficult areas (n≈4): radius ≈ 1.4×
Applying this to your current figures (~7–12 km):
- 7 km → ~10–14 km
- 12 km → ~17–24 km
Important notes:
- Antenna height (30 m) and line-of-sight often yield more practical gain than simply increasing power.
- Co-channel on 87.9 MHz (Goianinha/Executivo FM) will still be a limiting factor: increasing power will also increase the interference zone.
- Earth curvature and hills will remain the “ceiling” of usable range.

Topography is Key

In FM, it’s often more effective to invest in height rather than in power. FM waves, like any other waves, perform better when they encounter fewer physical barriers.

A good elevation means a greater visual range (a more distant horizon) and fewer obstacles, resulting in overall improved line-of-sight between transmitter and receiver. A tower surrounded by buildings, even with decent power, may face more difficulties than another located higher up, even if it operates with less power.

What Else Reduces the Coverage of Community Stations?

Sharing the same frequency is a mutually destructive factor. Nearby community stations end up creating mixed-signal areas. Often, two community radios just 7 km apart will lose significant portions of their coverage. Both are harmed: being slightly closer to a community does not guarantee acceptable audio quality.

In many cases, listening while moving will be confusing, and even at home, the radio’s positioning will be crucial in deciding between two or more stations coming in with some signal—yet still without guaranteed clear audio. A constant background hiss indicates that one or more other stations are “destroying” the chosen signal.

It’s as if, instead of tuning to a frequency and hearing it clearly, the listener had to move the radio around to find which signal stands out. This is common in areas where two, three, or more stations can be received on 87.9 MHz—the most widely used frequency for Radcoms. Although there are other frequencies allocated to community radios, the overlap on 87.9 is particularly common.

I’m Ricardo Gurgel, an engineer graduated from UFRN, and I try to share knowledge from this universe in a light and friendly way—like chatting with friends—avoiding overly complicated terms whenever possible. Soon, I’ll be bringing more posts on the subject, some with a more technical focus, others in a more informal style.

Instagram: instagram.com/blogdoRG.com.br

Case Study: Malembá FM

Freq.: 87.9 MHz – City: Senador Georgino Avelino

Coverage Map of Malembá FM

Despite operating with only 25 watts, Malembá FM can be heard with satisfactory quality in Pipa, about 15 km from the transmitter. It also reaches the city of Arês, located approximately 4.5 km from the station’s headquarters.

Areas Reached by Malembá FM’s Signal

Senador Georgino Avelino (city and station headquarters)

a) Tower: Reference point (0 km)

b) Signal: Excellent to good, with variations on hills

c) Obstructions: Occasional hills

Carnaúba (district of Senador Georgino Avelino)

a) Distance from tower: 2 km

b) Signal: Fair to good

c) Obstructions: Only vegetation

Arês (city)

a) Distance from tower: 4.5 km

b) Signal: Good in almost the entire urban area

c) Obstructions: Only vegetation

Patané (district of Arês)

a) Distance from tower: 1.6 km

b) Signal: Excellent

c) Obstructions: Only vegetation

Campo de Santana (district of Nísia Floresta)

a) Distance from tower: 5.7 km

b) Signal: Good in almost the entire urban area

c) Obstructions: Visible from the top of the tower, no obstacles

Tibau do Sul (city)

a) Distance from tower: 5.5 km

b) Signal: Interfered by 87.9 MHz from Nísia Floresta (Executivo FM), with possible satisfactory reception depending on receiver position and location in the city

c) Obstructions: Visible from the top of the tower, no obstacles

Pipa (part of the district of Tibau do Sul)

a) Distance from tower: 12 km

b) Signal: Good to fair

c) Obstructions: Slight topographic obstruction

Cabaceiras (district of Tibau do Sul)

a) Distance from tower: 6.2 km

b) Signal: Very good

c) Obstructions: Visible from the top of the tower, no obstacles

Munim (district of Tibau do Sul)

a) Distance from tower: 6.4 km

b) Signal: Very good

c) Obstructions: Visible from the top of the tower, no obstacles

Manibu (district of Tibau do Sul)

a) Distance from tower: 6.6 km

b) Signal: Very good

c) Obstructions: Visible from the top of the tower, no obstacles

Bela Vista (district of Tibau do Sul)

a) Distance from tower: 7.3 km

b) Signal: Very good

c) Obstructions: Visible from the top of the tower, no obstacles

Piau (district of Tibau do Sul)

a) Distance from tower: 8.1 km

b) Signal: Good

c) Obstructions: Visible from the top of the tower, no obstacles

Umari (district of Tibau do Sul)

a) Distance from tower: 8.2 km

b) Signal: Good

c) Obstructions: Visible from the top of the tower, no obstacles

Routes and Challenges

Heading west from Umari toward Goianinha, Malembá FM’s signal begins to compete with 87.9 MHz from Goianinha FM, which limits its reception in the neighboring city. A similar situation occurs when traveling from Carnaúba toward the BR-101 highway, where the signal conflicts with 87.9 MHz from Executivo FM in Nísia Floresta.

Even with these interferences, Malembá FM manages to reach a population considerably larger than that of its own municipality, Senador Georgino Avelino. This is due to favorable topographic conditions that allow the signal to propagate efficiently in communities along the shores of Lagoa Guaraíras—actually a bay—around which are located the cities of Arês, Tibau do Sul, and Georgino Avelino itself.

What if There Were No Other FMs on 87.9 MHz?

If Malembá FM were the only station operating on 87.9 MHz in the region, it would have the potential to cover—with excellent to very good quality—an estimated population of nearly 25,000 people, and with fair to acceptable quality, a much larger number of residents.

The 87.9 Model

The experience of Malembá FM shows that even with just 25 watts and a 30-meter tower, a community radio station can reach several neighboring communities with surprising quality—provided there is no interference from another broadcaster on the same frequency. Unfortunately, the Brazilian model, which forces all community stations to operate on the same frequency (usually 87.9 MHz), even in neighboring cities, creates a scenario of destructive competition for space on the dial. Instead of strengthening the right to local communication, this policy weakens community radios, harms the listener’s experience, and limits the true social reach of these broadcasters.

This centralized and restrictive model is, in practice, an exception worldwide. In countries like Argentina, Mexico, the United States, the United Kingdom, and others in Europe, community radios are allowed to operate on different frequencies within the FM band, based on technical studies that avoid interference. In other words, there is regulatory flexibility so that stations in nearby areas can coexist harmoniously, expanding diversity and strengthening regional communication.

In Brazil, the insistence on imposing a single frequency for all community radios—even in regions with high population or geographic density—needs to be overcome. Allowing alternative frequencies, based on technical and territorial criteria, would be a fundamental step toward democratizing the spectrum and enhancing the role of community radio as an agent of information, culture, and citizenship.

Technical Excerpts from the Survey