Best Antenna For FM, 7.8dBi Co-Linear 5/8

Best Antenna For FM

We think so simply because it delivers more gain, it’s physically stronger and it’s bigger than any other single based FM antenna that is available on the market for FM broadcasting. It also looks more elegant than the equivalent four dipoles on the side of a tower. Keep reading and looking at the photos and I’ll tell you more.

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Elvis and Alex

These two guys are Elvis and Alex who are employees of Aareff and have been working on this antenna now for around 3 to 4 months. When we first started this project I said we need to make the best antenna and the most powerful in a single unit that there is for FM broadcasting.

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Arriving On Site

We arrived on site in a small field about 1/4 mile from our industrial complex in Pisano, Santiago, Dominican Republic. The guys start to put the antenna together. Fitting the antenna to a mast or pole is easy on only requires a 13mm spanner to tighten up the two U Bolts.

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Clamping The Antenna To The Pole

In this close up photo you can see the base section with the two U bolts and how easily it clamps to the pole or mast. It’s easy to do this on the ground, but it’s also possible without too much trouble to clamp it in place if the pole is already on a roof or tower. The part you see with the yellow and blue rubber bands is the impedance matching inductor, the small round tube slides up and down between the bars to tune the antenna. this is only temporary for these field tests, the finished model will not have this.

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The DIN 7/16 RF Connector

Finger tightening the 13mm nuts up. You can see the the RF connector, it has a blue cover over it to protect it from damage. This is high powered 7/16 DIN connector that is silver plated and uses a Teflon / PTFE. If the connector is clean, in good condition and the coaxial cable is fitted properly, then power handling can be up to 3KW.

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Antenna Cable Loss

Final tighten on the 13mm nuts of the two U bolts and fitting the coaxial cable to the 7/16 DIN connector. We are using 20m of LMR400 to make the tests, this cable at 100MHz has a loss of close to 1.8dB, therefore the antenna cable will improve the measured return loss by double at a figure of 3.6dB or an VSWR of 0.2. This means that an VSWRof 1.3 measured at the end of the 20m cable is really an VSWR of 1.5 at the RF connector of the antenna.

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3/8 Wave Phasing Stub

The antenna is now vertical and looks amazing against the Caribbean blue sky. In this photo you there is a crystal clear view of the 3/8 wave phasing or delay stub. If your not familiar with radio terms, this is the coiled thing half way up the antenna on the white tube. Without this phasing stub the antenna will not radiate efficiently or give a gain of +7.8dBi to the horizon. I’m going to discuss in more detail in a later publication how exactly this works.

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Teflon/PTFE insulator

Another beautiful picture against the back drop of the Dominican sky. The white tube half way up the antenna is a Teflon / PTFE insulator. This material has excellent dielectric properties, there so good that the radio signal thinks the insulator is virtually invisible, not even there, just like air. Given this it can handle massive RF voltages without any heating effects.

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Panoramic View

A panoramic view in this picture. At four metres in length, this is a big performance antenna for FM broadcasting and is equivalent in terms of gain to four half wave dipoles mounted on the side of a tower that use at least ten metres of space. Looking up at the dipoles from ground, to the viewer they look ugly. Our 5/8 co-linear single straight vertical is elegant to look at and not too obtrusive, but has the same performance as the four ugly dipoles. Unless you have some unusual reason to use dipoles the 5/8 co-linear is the best antenna to use.

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Impedance Match

This picture shows a clear view of the base of the antenna. The 7/16 DIN connector is fitted, but it can be fitted with the smaller N type or SO-239/UHF Teflon / PTFE type if requested, but these smaller connectors will limit the power handling to about 1KW. The two inductor bars can be seen seen clearly, these form an RF transformer to match the 50 ohm input impedance to roughly 1000 ohms at the bottom of the main radiator.

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Design Strength

Another amazing view of the entire length of the antenna against the blue sky. This is the best antenna to use for FM due to the phasing stub that you see halfway up being physically very strong. It is made of solid 1/2 aluminium round bar. Believe we had to make several before we go the hang of bending correctly. The phasing stub is really rigid and screwed really tight to the white Teflon / PTFE insulator. If you’re wondering, it won’t distort or change in heavy winds. Not only is it the best antenna for FM, it is the strongest single antenna available.

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Bandwidth

The final full length picture, again a nice clear view from another angle of four main sections of the antenna, 1. the base, 2. the bottom 5/8 radiator, 3. the Teflon / PTFE insulator and phasing stub and 4. the top 5/8 radiator. The bandwidth of this antenna is really good for a non broadband type antenna. This particular sample was made for 89.0 MHz, the bandwidth was tested to be +/- 3.5 MHz to the 1.3:1 VSWR points, in the middle at 89.0 MHZ it was 1.0. That’s a total bandwidth span of 7 MHz which is 1/3 of the entire 88 to 108 MHz band. With just three models we can cover the entire band.

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Field Tests

This is Alex my son who works at the office between university classes studying Electronics. To prove this is the best antenna for FM available he is measuring the near field low angle field strength. It’s exactly as expected. At 2m from the antenna just below the ground plane rods we are seeing about -6dB (quarter power points) relative to the main lobe at 0dB and azimuth of 0 degrees. Right under the antenna ground rods next the mounting pole the field strength is zero, there’s no trace of RF. This is good and indicates that the phasing stub half way is working correctly, if not there would be “End Fire” out of the top into the sky and also out of the bottom into the ground. Later, not shown in the photos, we tested the antenna at 100m away using more power and confirmed that the main lobe was indeed at 0 degrees azimuth. We expected a little tilting upwards, maybe a couple of degrees, this is normal for 5/8, but no, it was solid at 0 deg with maximum radiation to the horizon. The field strength was double that of a single dipole, this is +6dB over a dipole or 4 times the power increase. This was sufficient evidence to verify our quoted figure of 7.8dBi was very close to correct and the antenna was working exactly as planned and designed.

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Solid Design

This is me Paul Hollings just demonstrating that I also like to get my hands dirty, this thing is heavy, the weight loading on the base section and the two U Bolts is enormous, but throughout all these tests the base section has remained sturdy, no buckling or distortion of the aluminium. It’s very strong because it’s also supported by a 2 inch diameter piece of Teflon / PTFE round insulator. Nothing in the base section moves, it’s solid.

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Successful Tests

Finally the tests are over and we lower it back to ground ready to return to our workshops and offices that you can see in the distance behind the trailers. It’s been an highly successful day and the results are everything we expected and more. This antenna without a doubt is the best antenna for FM broadcasting on the market, it’s the most powerful in terms of gain single antenna available.

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Thank You For Reading

Thank you for your interest in Aareff products and in particular looking and reading through this entire series of pictures. If you have any questions or comments, please enter them into this blog below.

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By Paul Hollings
https://aareff.com/paul-hollings.htm

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3 Comments

  1. Marino Sonnemans

    Dear Paul,
    very intersting project. I have done a similar project and even have tested 3x and 4x 5/8 for FM.
    currently I am using the 3 x 5/8 which also commercial available at Vigintos. the 7dB we make is verified by years of laboratory and field testing. Since 1999 we are tweaking and are happy with the result. Is it possible to buy your version?
    thanks for letting me know.
    Marino

    Reply
  2. aareff (Post author)

    Wow, 3 and 4 stacked 5/8, that must be massive.

    This is a great project, thoroughly enjoyable. Unfortunately we have had to put the Mamasita double 5/8 antenna on hold for the moment, so we are not selling them right now, but we want to and the will is there to do so.

    The reason for the hold up is that when we first published this here in the blog and on Facebook we had some fierce criticism about our gain figure of 7.8dBi. Many of enthusiasts said that this gain was not possible and sent various simulations to me to support this. I planned on running the simulations and doing more practical tests, but we just run out of time and I had to concentrate my time on other areas of the business to make sure we kept the money coming in, rent paid, wages paid etc.

    We did sell one to a station in Africa, they replaced our 4 way stacked dipole with this. The 4 way stacked dipole has more gain, but it has a height disadvantage being mounted on the side of a tower. We figured that the double 5/8 being mounted at the top of the tower might just perform better with greater range. Unfortunately the station have not responded to our requests for information about how the antenna is performing and how it is physically coping with climate there sat on top of a 40 meter tower. I will keep trying to contact them.

    When we have some free time again, I want to make another one of these and mount it together with a standard dipole. Basically the double 5/8 on top of pole and the dipole just below. Feed them both with two unmodulated separate 1W signals, very close in frequency, only 0.1 MHz between them. Then view both carriers simultaneously on the spectrum analyser while driving around various locations. If the antenna is working as we hope there should be an average of at least 5.5 dB between the carriers, obviously the gap will change due to different effects, but if we can get that average of more than 5.5 dB we can then be more confident to challenge the simulators and start going into production with these.

    We have had a lot of interest in this antenna, a guy in New Zealand a few weeks ago was desperate for one, but we couldn’t supply, not yet. 🙁

    We’ll get there soon.

    Paul Hollings.
    http://uk.linkedin.com/in/paulhollings

    Reply
  3. marino sonnemans

    Thanks Paul for your comments.
    I can understand the feedback on the 7.8 dBi. it is very difficult to prove it is there and also what angle exactly is achieved. I can show you test results from our accredited antenna laboratory and we decided to lengthen the top radiator, shorten the delay line to create down tilt and achieve the 0 degree. for the 3 x 5/8 (pictures in our tower I forwarded to you) we achieve the 7 dB with 0 degrees after tweaking for months. the bandwith has become more narrow but performance is superb. construction wise the delay lines we kept in the antenna. the 4 x 5/8 is not worth the effort. our proto is working however the practical performance is not better as the 3 x 5/8 on FM. role of ground and ground planes is increasingly influencing the behaviour with the growth of stack number. let’s continue via the mail so we will not mess the blog with comments of people knowing all. Thought it was good you know we are busy with 3 and 4 x 5/8 as well on broadcast.
    Marino (SunnyboyFM for insiders in the Netherlands)

    Reply

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