FM Radio Station ANTENNA ARRAY FM Transmitter Set Up. Get It Right For Best Signal Quality.

How to build FM radio station antenna array. A 2 stack and 4 stack FM dipole antenna arrays. Boost your FM signal of your radio station with multiple dipole antennas. Without all the scary technical equations and antenna design theory, you can build your own FM dipole antenna array.

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A great way to increase your radio station signal power is to build multiple antenna stacks otherwise known as an antenna array. Today we look at FM transmitter antenna arrays that you can build yourself. We look at how it’s done, what parts are needed, and when to avoid building an antenna array.
If you do some research on FM antenna array construction you will go down a rabbit hole of technical theory that you may never make it out of. The theoretical study of antenna arrays is one of the most complicated and often confusing forms of engineering around.
This video intends to give a simpler explanation and some practical ways to build antenna arrays without having to rack your brain with complicated equations and theories.
When most newcomers to building radio stations decide to build an array it is because their transmitter does not provide enough power so it needs to be increased by adding more antennas. In some cases, people simply want to run the transmitter at a lower power level to extend the life of the transmitter. Whatever your reason, the antenna stack or array can double and quadruple the output power of the FM transmitter. This is by using a two-stack and a 4 stack. In theory, it is possible to build even bigger stacks such as an 8 stack but it actually becomes impractical beyond 4 antennas because of the sheer size of the antenna stack. A 4-stack antenna is at least 8 times the size of a single antenna length.
Unless you have a massive antenna mast that is completely vertical, this is not the way to go. You would be better off buying a transmitter that is more powerful.
Let’s look now at building a simple two-stack antenna array. The parts you will need are two antennas, a pole at least 4 times the length of the antenna, and the most important part is what is known as a harness. This is essentially a few pieces of coaxial cable joined together.
You may be wondering what this strange collection of wires does. To understand the importance of the harness we first need to see how the antennas are connected together and how they work together in unison to amplify the radio signal. When two antennas fire off the radio signal at the same time, at a certain point the two signals will intersect. It is where these signals intersect that the signal can be amplified by adding the two signals together or cancelled out by the two signals being in opposite polarity when they meet.
In the 2-stack antenna array, the FM dipoles are spaced half a wavelength apart. To understand why we can draw a full wavelength across the antennas. As you can see, at exactly a half wave spacing, the two antennas are at the exact same polarity at the same time. This is when the two signals can work together but if you feed the two antennas out of phase they will not be working together even if they are spaced correctly because when for example the positive part of the wave reaches the one antenna, the negative part will reach the other antenna because the radio signal has further to travel along the cable to the second antenna. To fix this we use a harness that is two quarter wavelengths long. This allows the radio signal to reach both antennas at the same time. These cables must not be tuned or adjusted but simply connected to each antenna. You could make these cables yourself but most people have found it simply easier to buy premade harnesses as getting the impedance matching right is very difficult. They are not tuneable so in essence as long as the lengths of the two arms of the harness are exactly the same length and approximately a quarter of a wavelength long they can work together. You can simply place a T-Piece cable adaptor where all three cables intersect, creating the harness as a big t-piece cable. This is simple enough for a two-stack array but a little more complicated for a four-stack but we will get to that in a minute.
Something important to mention here is when you are setting up your antennas. The spacing between the dipole antennas and the pole they are mounted on needs to be exactly a quarter wavelength. The reason for this is that the reflection from the pole can help or hurt your signal. At exactly a quarter wavelength spacing the reflected signal from the pole can add a dB or two of gain but if the spacing is wrong it can actually cancel out some of your signal.

[crankshaft]

Wow! Brilliant work! I was technical direcotor at a 100 thousand watt FM station here in the US. This means that when the federal autorities came calling it was MY name on the paperwork.

One tip I would add to what you say is:MILLIMETERS MATTER. Down in the Ham bands you can be off a cenimeter or so and be OK. At our frequency, no. Remember that you can triim more off nut you can't put more on.

At my power level we used 63 millimeter copper pipe with a 6 mill ceter conductor. We pressurized the line with Nitrogen gass to keep it dry. You folks that can do this with regulat coaxial cable are lucky.

[gfvt]

I am glad that you mentioned down tilt, it can significantly help with coverage in the local area. Phasing harnesses are not difficult to make and we do have plenty of test equipment available these days to make the measurement easy.

[dariuszmular]

Hello! Thank you very much for the compendium of knowledge in a nutshell. This steak is full of meat :-) everything you have included in this recording is enough to build your own stack of antennas. I will build my stack at 435Mhz because I have noticed very high losses in multi-band antennas such as diamond X200 X300 etc. In this band, a smaller single-band antenna can work better than large multi-band ones. Greetings and thank you for sharing this knowledge in an easily digestible form.

[merlingriffin]

Actually antennas don't make or amplify power. They can direct it where it needs to go. When we stack the dipoles on top of each other as this video shows, it forces more signal outward and less straight up and straight down. Now in most cases the station doesn't want to radiate straight up, and probably not straight down. In most cases the antenna is out in rural areas. Now they don't want the signal to pass over a close by town, especially if its one they are licensed to cover. So, they may have a bit of down tilt or steer as the broadcast engineer mentioned in his comment. I proved one day that this is really a thing. I am s ham radio operator. I maintain one of the 146.88 MHz repeater in town. We had taken our four element antenna array down for repair and was temporarily using a 5/8 wave antenna. The 5/8 wave antenna could receive an operator about say 10 miles away perfectly. He was transmitting with about 2 watts on a hand-held. There was another operator about 50 miles NE of us on the interstate highway running about 25 watts into his 5/8 wave antenna. The repeater couldn't hear him well at all, but when I switched over to the four element 6 dBd array antenna then the mobile operator came in full noise quieting and we couldn't pickup the guy on the HT anymore. By the way we were standing 750' above the ground while conducting this experiment. For my purpose I need an antenna with both characteristics. One that can cover 50-60 miles out and at the same time, cover the guys in town too. So I'm trying a multi receiver concept. One receiver in town, and two out in high places on the edges of town.

[skycrew]

Small note, in a large band system covering the whole FM band ( for multiple broadcast frequencies, [multiplex] ), you need large band dipoles and a coupler. Same length for all cables still applies between antenna elements and coupler to get -in phase-. The total system gain is also a factor of power loss ( insertion loss VSWR ) losses in cables, connectors, coupler, any cavity filter.

[carlfon]

Yes intrested in making my own antenna.

[jhonsiders]

We run a .95 wave Norwalk vertical at just 10 watts FM can get out about13 miles the transmitter can go up to 150 watts but that is pushing to get in trouble 👿 the reflective is zero at ether output I did have a1/4 wave home built ground plane that was flat too with a bit of fiddling with it it was PVC pipe and copper tubing with the SQ soldered to it . The worst antenna was a circular polarized one it had no range at all . I sold that on eBay to a guy in NYC that could vise grip it to his fire escape to do his show then remove it . Worked great in the big city. We have a 40 foot tower out here .

[namesjames]

Good evening...What is the best antenna for 30watts transmitter?

[jandersondemori]

Hi friend, I've damaged several power transistors because rain flash light, could you tell how to protect my transmitter output ?

[customsoundltd.]

Where can you purchase the transmitter and the set up equipment.

[mahmoudalfanny]

Hello, can you explain the two 3Dbi antenna, for example, 99.7 mhz

[DiosconnosotrosI]

Hello!! What's the best antenna for 1KW transmitter? Thank you

[JamesHalfHorse]

Interesting. I only have one single bay FM. All the others are taking 10kw and making 25kw, 20kw making 50kw and 30kw making 100kw all through the magic of antenna gain in multiple bays on the towers.

[Sonnyblack]

What is a wavelength ? As in wavelength apart ?

[HIFISOUNDS]

please suggest antenna for portable fm transmitter.100mw

[Ressy]

@2:43 Isn't the spacing supposed to be half wavelength from centre to centre, unlike this time-point which shows bottom of 1 to top of second.

[nakayle]

This video only talks about about vertical polarized antennas. Commercial stations use bipolar or circular polarization which works better since not all receiving antennas are vertical.

[SX]

The whole opening premise of this video is WRONG. One does not increase transmit power by adding or stacking antenna, so misguided. Antenna arrays only serve to concentrate the power you are producing in direction or horizontal plane. Respectfully, Dennis KV4WM