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Ask Slashdot: DIY 4G Antenna Design For the Holidays? 135

Posted by samzenpus
from the tune-in dept.
eldavojohn writes "This holiday season I will return to the land of my childhood. It is flat and desolate with the nearest major city being a three hour car drive away. Although being able to hear the blood pulse through your ears and enjoying the full milky way is nice, I have finally convinced my parents to get "the internet." It's basically a Verizon Jetpack that receives 4G connected to a router. My mom says it works great but she has complained of it cutting in and out. I know where the tower is, this land is so flat and so devoid of light pollution that the tower and all windmills are supernovas on the horizon at night. Usually I use my rooted Galaxy Nexus to read Slashdot, reply to work e-mails, etc. I would like to build an antenna for her 4G device so they can finally enjoy information the way I have. I have access to tons of scrap copper, wood, steel, etc and could probably hit a scrap yard if something else were needed. As a kid, I would build various quad antennas in an attempt to get better radio and TV reception (is the new digital television antenna design any different?) but I have no experience with building 4G antennas. I assume the sizes and lengths would be much different? After shopping around any 4G antenna costs way too much money. So, Slashdot, do you have any resources, suggestions, books, ideas or otherwise about building something to connect to a Jetpack antenna port? I've got a Masters of Science but it's in Computer Science so if you do explain complicated circuits it helps to explain it like I'm five. I've used baluns before in antenna design but after pulling up unidirectional and reflector antenna designs, I realize I might be in a little over my head. Is there an industry standard book on building antennas for any spectrum?"
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Ask Slashdot: DIY 4G Antenna Design For the Holidays?

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  • by Anonymous Coward on Friday November 30, 2012 @09:15AM (#42140605)

    As the Jetpack is so small, could you mount it inside a parabolic dish - i.e. WOKtenna?

    See: http://www.usbwifi.orconhosting.net.nz/

  • by robot256 (1635039) on Friday November 30, 2012 @09:16AM (#42140611)

    At the higher frequencies like 1.3GHz (LTE), the wavelengths are so small that the corresponding antenna features are also very small. They have to be extremely precise if you want the gain to actually be at the right frequency, and even then it usually takes some trial and error. Do you have a chemical or laser PCB etching machine, and a cellular antenna analyzer (Saw one SUPER cheap on ebay for $300 once). Otherwise, just making random things could result in reflections damaging your transmitter. This isn't like putting together a 1/4-wave dipole on 2 meters.

    But you could try fashioning a parabolic reflector dish and put your existing antenna in the center of it. I've heard of people doing that with cell phones and wi-fi adapters before.

  • by emmjayell (780191) on Friday November 30, 2012 @09:18AM (#42140627)

    How about posting some pictures of the milky way? I've only barely seen it once while on Hilton Head island.

    http://www.dslreports.com/forum/r27484816-DIY-3G-4G-LTE-Yagi [dslreports.com]

    http://bcbj.org/antennae/lte_yagi_diy.htm [bcbj.org]

  • Re:30$? (Score:3, Informative)

    by putty_thing (637042) on Friday November 30, 2012 @09:21AM (#42140639) Homepage
    I was joking originally but just Googled [google.co.uk] it, a lot of the used 4G frequency range is pretty close to the 2.4Ghz that has been used for wifi cantennas, looks like you can build something pretty easily.
  • LTE yagi (Score:5, Informative)

    by HoaryCripple (187169) on Friday November 30, 2012 @09:30AM (#42140675) Homepage

    http://bcbj.org/antennae/lte_yagi_diy.htm [bcbj.org]

    Decent instructions for an LTE yagi.

  • by Fishead (658061) on Friday November 30, 2012 @09:35AM (#42140705)

    Myself, I'm a newb radio technician, so I know where you're coming from.

    What you want is a "Yagi" antenna. Very directional and therefore, longer range.

    Search for "Cantenna"

    Also try: http://www.skyscan.ca/Antennas.htm [skyscan.ca]

    I had previously found a website that had a good modeling program to show you the lobe of radiated power, but don't have time this morning to find it again.

    I'm also not sure what frequency you want to build it for. Some sites say 700mhz, some 1800mhz.

    Hopefully someone with more radio know-how can add to the discussion. If you're near south-east BC, bring it by and we'll test the antenna on my (absurdly expensive) service monitor. I'm wanting to build a long range wifi net connecting to several buddies in town, so I'll be watching and hoping for some insightful help on this thread.

  • by olsmeister (1488789) on Friday November 30, 2012 @09:44AM (#42140761)
    If it's Verizon 4G LTE, it should be 700 MHz. They use 850 MHz and 1900 MHz for their 3G stuff.
  • What band? (Score:3, Informative)

    by Anonymous Coward on Friday November 30, 2012 @10:17AM (#42140977)

    LTE doesn't really mean anything for an antenna designer. It's all about modulation type, rate and protocol. What matters for antenna design is center frequency and to some extent bandwidth.

    In North America, there are several LTE bands in use: 700/800, 1700/1900 and 2500 MHz. If you can, find out what bands Verizon uses in your area.

    Don't buy a cheap 2dBi antenna. The antenna in the module is probably around 0dBi already so it won't help much. What you want is a directional antenna you can point at the tower to get a big improvement. The good news: this IS something you can build yourself. If you need to cover all three bands, you'll might need a log-periodic. If it's one frequency you can build a Yagi and it will do better than the log-periodic.

    Books for antenna design for amateurs:

    AARL Antenna Book

    AARL Wire Antenna Classics

    There are more books that are written at various levels. I suggest the AARL books because they assume you have some technical knowledge but aren't necessarily an electrical/electronics engineer. You can also find free designs on-line for antennas made by radio amateurs. These are often very helpful and tell you exactly how to build their antennas and show you pictures. Some engineering and science libraries will let the public come in and peruse their books. If so, you can go there with a pad and pencil and design your antenna right in the library.

    Since your antenna will be bidirectional (same antenna for up and downlink) you will need to use low-loss cable to connect them up. This is very important because if you use the wrong cable or too long a cable, you may overcome the gain of the antenna! That's another reason to build a high-gain antenna.

    Pointing a high-gain antenna at the tower also gets your RF out of the house where it's less likely to interfere with other stuff that might be in your house, like phones.

  • A cantenna is NOT a Yagi. It's a waveguide antenna.

    And a cantenna at 700 MHz is barely feasible. Anything with acceptable gain is going to be absolutely gigantic. You would need a proper Yagi at this point.

  • by StatureOfLiberty (1333335) on Friday November 30, 2012 @10:41AM (#42141217)

    To answer your question about digital TV antennas:
    Despite the marketing implications, there really is nothing different about antennas for Digital TV. The encoding is not important. The frequency is the main factor and that has not changed substantially. Most digital TV stations are on the UHF band around where I live. So, if you are lucky, you can get by with just a simple UHF antenna if the stations are nearby.

    Here is where you can find your nearby stations:
    http://transition.fcc.gov/mb/engineering/maps/# [fcc.gov]

    I built a simple 4 bay bow tie antenna for UHF. Mine looks like the one pictured at the top of this thread.
    http://www.city-data.com/forum/consumer-electronics/614073-how-build-your-own-4-bay.html [city-data.com]
    Here is a really nice example of one:
    http://www.dtvusaforum.com/dtv-hdtv-reception-antenna-discussion/8629-kosmic-antennas-superquad-4-bay-bowtie.html [dtvusaforum.com]

    I also built a folded dipole for VHF: Here is an example:
    http://crdahl.com/antennas/dipole.html [crdahl.com]

    My stations were fairly close by. These two antennas are not high gain antennas. I added a Winegard preampt to bring up the signal a bit. I have been very pleased. So, in summary, there is nothing different. Just look up your local stations and pick an antenna based on band(s) and distance.

  • by LWATCDR (28044) on Friday November 30, 2012 @11:26AM (#42141763) Homepage Journal

    I would go with a Yagi or a multi element beam. http://en.wikipedia.org/wiki/Yagi-Uda_antenna [wikipedia.org]
    You could start out with just a half wave dipole .
    Here a a very good site to get you started.
    http://www.antenna-theory.com/ [antenna-theory.com]

  • by Zalbik (308903) on Friday November 30, 2012 @11:51AM (#42142085)

    I disagree. For $120 you are basically getting exactly what the OP described in one of his responses: a bunch of metal configured in a certain way.

    Antennas are one of the easiest "geek projects" to do, and if the OP has access to the materials described, it should be a fairly simple (2-4 hours) project...

    Actually, just googled "DIY LTE Antenna" and came across this [dslreports.com] . Apparently 4 hours to build, and cost all of $10.

    Sure from a pure time/money perspective, you are only saving $27/hr, but IMHO it's time well spent.

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