FM Radio Station ANTENNA ARRAY FM Transmitter Set Up. Get It Right For Best Signal Quality.
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- Опубликовано: 1 июн 2023
- 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. 
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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.
Hey. Thank you. This video took a ton of work to make so it's nice to see people appreciate it lol. Yeah on 88-108 Mhz everything can be critical to the last last centimeter that's why I recommend people buy the harness. There's more than enough other stuff to worry about and making a harness can be a real pain. Yeah I have mostly worked with low power radio stations of just a few hundred watts so it not as crazy as your high power stuff. So we can get away with using RG213 and even PL259 connectors. Mostly N-type but nothing crazy like yours. Can't imaging having to deal with all that. And yeah having your name on the docs is a little scary lol. Cheers.
How did the Ariel hold all that power , I would have thought they melted ?
@@Sonnyblack100 100 KW is quite common herein the US on the FM band. Old style TV transmitters here had power in the millions of watts. Digital TV dropped the powere way down.
Back in my days at the FM station our next door neighbor was a high power TV. Indeed their power line never had ice on it on the coldest days. Power is great fun if you know how to handle it and YOU play by ITS rules.
@@crankshaft3612 I would love to run a 1000 wats in London with double stack aerial
@@Sonnyblack100 Remember yourHAAT my friend. That is Height Above Average Terain. The whole fomula is (Transmiter power) times (Antenna Gain Factor) times (HAAT). So if you are mobile among big building your HAAT becomes a loss factor. Oh, and don't get caught.
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.
Hey thanks for your comment. Yeah if you are set up with some nice test equipment it can be done but a lot of my viewers are new to transmitters and antennas so have very limited access to test equipment. Yeah thought I'd mention the down tilt even though it's too complicated to give it the explanation it deserves in this video. Maybe in another video some time :) Thanks cheers.
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.
Hey thank you for the nice comments. Always nice to be appreciated thank you :) I'm glad you enjoyed the video. I try my best to make my videos have enough info to be worthwhile to watch but not too much to overwhelm people. I also try to focus on broadcast FM band because that's what most of my viewers want but I have heard of other people converting my stuff for other bands. In most cases it is just a change of measurements but, as you say, some things don't translate as well as that across different bands. Always fun to experiment anyway :) Nice to have you watching. ENJOY.
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.
Thank you for your comment.
Waiting for next video
Hey that's awesome thank you. Working on it. Let you know when it's ready. Cheers :)
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.
Hi. Thank you for that. It's always great to have extra input from people in the industry with your level of expertise. The vast majority of my viewers are first timers so it might be a bit over some people's heads but always great to have some extra insight. Thank you.
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 .
Thanks for your comments. Yeah I normally would not recommend circular polarized antennas unless a very experienced and equipped person installs and maintains it. Circular can easily become a problem. If done properly circular polarized antennas can be great for built up areas and cities but other than that can be more of a problem than it's worth. Cheers.
Hi friend, I've damaged several power transistors because rain flash light, could you tell how to protect my transmitter output ?
Hi. There is only one way really to protect your transmitter and that is with a lightening arrester which you place between your transmitter output and the antenna cable and then put a deep spike into the ground or attach to a water pipe that is earthed to the outside of the arrester. They are quite cheap and very easy to install. But buy the best one you can. Here are some links to ones on Ebay but you can buy them in many places. tinyurl.com/zh92tk45 or this one tinyurl.com/3tuu2jaf but make sure you choose one with the right connectors on it to fit with your cable connectors or you have to use adaptors that lose a bit of signal. Go to 7 minutes and 30 seconds 7:30 on this video of mine to see more about this ruclips.net/video/mmGQQo2X1vY/видео.html
Good evening...What is the best antenna for 30watts transmitter?
Hi. It depends on what you want to do with the signal. If you want it to be omnidirectional then antennas like a quarter wave can work or if you want to add some gain to your signal to increase its strength a 5/8 antenna is better. I have a video about the different types of antennas for FM. Check it out here: ruclips.net/video/mmGQQo2X1vY/видео.html
Also, make sure the antenna is tunable. To find out more about that check this video out:
ruclips.net/video/WOGX70-kIYA/видео.html
A slim jim type.
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Merci beaucoup :)
Thank you so much :)
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.
Yeah it is amazing especially at such high power. Crazy that stations can run 100Kw. Very cool. Glad you enjoyed the video. Cheers
@@inspiresoundpro I will keep an eye on what you got going on. I like it when people can break down the complex. I am still a novice engineer/electronics/computer shop. I am the only one left in the area willing to work on the equipment. I can follow along with schematics and mostly understand the engineers when I call the manufacturers after I tell them they might have to dumb it down a bit. Antenna theory/science is all but voodoo to me especially how the bays work but you explained it in a way that makes sense to me. The phase and the spacing without going too deep into the weeds. I have been thinking about applying similar to amature bands but not sure it would work. After seeing Ringway Manchesters series on the duga radar I am curious about caged dipoles too as it seems to be a wall of them. I also promised my great niece I would bounce her voice off the moon so I best get to work. I gave her an old amplifier tube for show and tell last visit.
Wow you are into some cool stuff. I have only had a small amount of experience with HAM stuff but it's lots of fun. A lot of the FM stuff can be adapted to HAM and some say it's a lot easier with HAM stuff especially on the lower frequencies but the antennas get much bigger so a bit difficult with that. Thanks for your nice comment. Yeah I try my best to make my videos as easy to understand as possible because most of my viewers are trying to build stations and transmitters for the first time so the technical stuff can be very overwhelming. I have a college education in electronics and I struggle to understand some of the antenna theory lol so I can image what the beginners feel like. Cheers .Good luck with the moon bounce. That's well cool :)
@@inspiresoundpro Well I have an 8th grade education but I started out soldering simple circuits for my dads model trains when I was like 6 or 7. I learn with my hands and got into the IT side of things when what you could do meant more than what formal education you had. The engineering stuff came along as I started working on automation computers that ran the station. That had me wiring stuff up so the engineers took me in and became my mentors/elmers. One has already gone silent key. The other is nearly there and slowly giving me his shop equipment. Just his meters and soldering station alone is like a master machinist turning over his calipers. Not an easy thing but an honor to me. I can mostly follow along when it comes to RF thanks to them and I have been learning a lot from the amature guys like you on here. If you want some good basic education on RF, inductance, capacitance, etc look up Periscope Films on here. Old 1940s military training videos designed to teach us bumkins out of the hay fields how to repair radios so they are very easy to understand. Might be a good place for you to mine for content.
Kindly send details
I want to build my own antenna
Yeah building your own FM antenna is very cool and fun too. I will make a video on how to build a half wave dipole soon. Been a bit busy but will make new videos again soon.
please suggest antenna for portable fm transmitter.100mw
Hi. I am busy working on a video for making antennas. But for a portable one I would recommend using an antenna that gets used for CB Radio and cutting it shorter. I will explain more in my video but what you need to do is get what is called a magnetic mount center load antenna . This is used on 27mhz . You need to remove the center load and replace it with a long telescopic antenna that you can get from an old FM radio. The total length with the antenna pulled out should be a quarter wavelength long so about 75 to 80 cm long from the magnetic base to the tip of the antenna.
Am working on the video now and it should be ready by the weekend I hope.
@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.
Keep in mind that the radials are a quarter of a wavelength each. So if you were to make the spacing from center to center the two antennas would touch as they would be 2 X 1/4 wavelength = 1/2 wavelength. The spacing would also not make sense because the antennas would be completely out if phase. Another thing to consider is that with the two antennas touching there would be no space for adjustment to create down tilt.
@@inspiresoundpro thanks, makes sense :)
The wavelength distance is in between dipole radials,
in between brackets the distance is 2,1m
What is a wavelength ? As in wavelength apart ?
Hi. Thanks for your question. Every radio frequency has a specific wavelength. The wave length is the measure of how long a radio wave is as it goes through a complete cycle. This gets very technical but is simpler to understand that the higher the frequency of the radio wave the shorter the wavelength. So for example radio station signals for FM have longer wavelengths than microwaves. Microwaves have a high frequency and a short wavelength. You can work out the wavelength of every frequency but using an equation but it is easier to use a wavelength calculator. If you watch my video about tuning your FM antenna you will see the wavelength calculator. You insert the frequency and it tells you the wavelength. I hope that helps.
Thanks , I was thinking the space between each diapole was in fact the length of the diapole , so the gap between each diapole is in fact a your diapole length, or do you still need a calculation ?
Thanks for replying
I’m talking the gap between the double stack
The gap between the antennas is measured from the top of the bottom antenna to the bottom of the top antenna. The measurement is half a wavelength which is calculated the same as calculating the wavelength of the antenna. The gap is not always exactly the same length as the antenna. It is normally very close but other aspects like how well the antenna is built can make the length of each antenna slightly different in length. Normally a very small amount but the gap must be exactly half a wavelength. So there can be a difference between the antenna length and the gap but normally a small amount.
Thanks for that in depth reply 👍🏼
Kannada
Glad you enjoyed the video. Cheers