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Home > News > FM Broacast

How much distance does a radio transmitter reach?

Published:2022/1/11 15:47:08 Visits:
How far will an FM transmitter broadcast?

Some customers often ask us for some professional radio equipment knowledge, such as “How to build a complete radio station at low cost?”, or “How to choose dipole antenna for my high power FM transmitter? 6-bay dipole antenna or 8 bays?", etc. The interesting thing is, they are much more curious about the range of an FM radio transmitter and have raised so many related questions to our RF engineers. And the following content is part of the frequently asked questions list on FM transmitter range and the corresponding share. We hopefully believe this share on transmitter coverage can help you solve your problems, whether you are one of our customers or not

Common questions asked from our customers:

How far can a 1-watt radio transmit?
    How far will a 1 watt FM transmitter reach?
    How far will a 5-watt FM transmitter go?
    What is the 15w FM transmitter range?
    How far will a 15w FM transmitter broadcast?
    What is the kilometer range of a 15W FM transmitter
    What is the FM transmitter range chart?
    How far will a 100 watt FM transmitter reach?
    How far will a 5000 watt FM transmitter reach?
    How far can a 50000 watt FM radio station reach?
    How to calculate the FM transmitter range/FM transmitter range calculator?

Interesting thing is, when our customers want to know the coverage of our radio broadcast transmitter, we will always state in advance: "You cannot have the accurate number of the coverage range of an FM broadcast transmitter (regardless of power or type), unless you are in the laboratory! "The reason why we can explain this to our customers is that according to the observation of our RF expert team, there is more than one factor affecting the broadcast coverage of the transmitter. Effective radial power (ERP) and the antenna site height above average terrain (HAAT), and many other variables are also important factors we need to consider.

Therefore, in order to satisfy our customers with actual answers and help solve practical problems, our RF engineers and sales team usually give some specific numbers. For example, for customers who ask about the coverage of low-power transmitters, we usually say: "15W FM transmitter can cover up to 3k㎡, while 25W FM transmitter can cover up to 5k㎡. If you want to cover a wider range, such as 10k㎡ or 20k㎡, you should choose a 150W or 350W FM broadcast transmitter because they are larger in transmitting power"

However, for some radio newbies, these accurate figures may cause unnecessary misunderstandings and push them into thinking factors that will affect the coverage of an FM radio transmitter. Although the corresponding answers are hard-won, we still summarize the following factors that can determine the coverage (which means how far they can go) of an FM transmitter:


1. The broadcast transmitter output power amount (TPO)

TPO is abbreviated from “Transmitter Power Output” in the field of wireless communication, it actually refers to the outputting power produced by a transmitter, if you were told that "This is our top-sales 5kW FM transmitter", then this "5kW" is always seen as the ERP power (Effective Radiated Power) instead of the actual transmitter power. TOP is closely connected with cost, buying, budget, etc., which is mainly because a wider ideal coverage comes with a higher buying price for some of the radio station equipment such as an FM broadcast transmitter and FM radio antennas. Therefore, TOP, together with antenna gain, are two of the most important factors that should be taken into consideration especially in the early period of radio station buildup, when you're deciding which brands and what equipment is best for your budget.

2. The Antenna placing height above average terrain (HAAT)

In radio broadcasting, HAAT or EHAAT(effective HAAT), or height above average terrain actually refers to a vertically comparable distance between a transmitting site(transmitter and antenna are included) and the average terrain height among few kilometers. To reach a common understanding of the HAAT key points, one needs to know that HAAT is basically the coverage of a broadcast antenna, it is the vertical position of an antenna site is above the surrounding landscape. Suppose you are standing at a position flush with the installation site of the antenna, at this time, you and the transmitting site are on a plain, then the antenna may reach a tens of kilometers distance for broadcast. If your position is not a plain but a hilly area, the broadcast distance may reach only several of kilometers. HAAT is officially measured in meters, which is widely recognized by international coordination, and of course by regional radio organizations such as the Federal Communications Commission (FCC).

This also reminds us that if you want to obtain the maximum coverage when the transmitter, receiver, antenna, and accessories are ready, always remember to place the antenna as high as possible, so as to obtain at least 60% clearance in the Fresnel area and get real RF line of sight (LOS), plus, it helps avoid the negative factors to stop the RF range from expanding, such as the dense trees and high buildings, etc.


1) Due to the lower antenna height, the loss in the RF cable is smaller, and the antenna may work in a better condition at this time, so think of the trade-off between the antenna height and the number of RF cables required.

2) After the assembly of hardware broadcasting equipment, please be sure to pay attention to the local radio administration's regulations on antenna height to prevent penalties (in some areas, the penalties for the inappropriate antenna height are quite heavy).

Tips: Definition to Fresnel Zone in Radio Frequency

Application: Physical area

How it generates: the transmitter and receiver are at the line of sight

What it belongs: radio wave

What does it mean?

The Fresnel region is between the transmitting and receiving antennas, and the travel difference between the straight path and the broken path of the radio wave is n λ/ 2 is an ellipsoid with the position of the transmitting and receiving antenna as the focus and the straight path as the axis. The size of the ellipse is determined by the operating frequency and the distance between the two stations. In the field of wireless communication, to ensure the best working conditions for the whole system, one thing that matters is keeping a clear elliptical passing area between different antennas on both broadcast sites, making sure there are no limits, no stoppages, no obstructions for the processing.

Why it is important?

Because any interference or obstacle in line of sight (LOS) may cause signal loss, in point-to-point wireless communication, it is important to keep the line of sight between two wireless systems free of any obstacle

3. Types of antenna and accessories that used in the antenna system
types of antenna and coaxial cable used
amount of coaxial cable used

4. The sensitivity of the FM receiver at the other side

Irreversible factors
1. The degree of emptiness in the terrain around the antenna site
encumbrance that surrounds the antenna site, such as the density and height of trees or buildings

2. Type of terrain near the antenna site
flat or hilly

3. Radiofrequency interference due to same frequency broadcasting from near radio station

The near frequency stations or other radio stations broadcasting in the same frequency, for example, the antenna may be able to see 20 kilometers, but if another station is on the same frequency 20 kilometers away, it will block/interfere with the signal

The truth is: you can never determine the exact coverage of a broadcast transmitter no matter the transmission power or brands it belongs to. Fortunately, you can always obtain the estimated coverage of some radio broadcast transmitters from the RF experts (just as we did earlier).

These estimated numbers do goods in actual practice-to help you think twice before choosing a good broadcast transmitter and reduce unnecessary costs or expenses, or be well-referenced in after-sales services or any online technical support after buying an FM transmitter.

Of course, we all know that experience is the best teacher. To set up an FM transmitter and run it directly may be the best way to obtain the most accurate coverage of an FM radio transmitter.

FMUSER hereby suggests that you can try to use different variables and conduct multiple experimental comparisons, for example, you can:

1. Determine the type of antenna (4-bay or 2 bays FM antenna is great)
2. Determine the wielding height of the antenna (30 meters is pretty enough, that equals to a 15 story building)
3. Determine the power of the radio transmitter (you can also change 200 Watts to 500 Watts, and vice versa).
4. Find different sites as the transmitting point (consider whether you are in a flat or hilly area or right on a mountain)
5. Record the farthest broadcast distance you can receive clear radio signals from the transmitting point
6. Change the variables and make comparisons to what you record.

If you find that there is nothing you need in the transmitter coverage reference table provided by us, please let us know the first time. FMUSER can help you estimate the coverage of your radio transmitter.

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