Field Testing A Home Made WiFi Antenna

Most readers will be aware that a good way to extend WiFi range is to use a better antenna for those 2.4 GHz signals, but at the same time such high frequency hijinks have something of a reputation of being not for the faint-hearted. [Dereksgc] puts that reputation to the test by building a helical WiFi antenna — and if that weren’t enough — he also subjects it to a field test. In a real field, is there any other way?

We’ve put both videos below the break, and you can find his helical antenna calculator on his website and the parametric CAD file for the scaffold in his GitHub repository. He first delivers a crash course in the fundamentals of helical antennas before diving into the construction, and even soldering on an impedance matching strip. The field testing involves setting up a base station with an FTP server on a phone, and connecting to it with a variety of antennas over increasing distance across farmland. We’ve characterised antennas in this way before, and it really does give an immediate view of their performance.

In this case the helix comfortably outperforms a commercial patch antenna and a laptop’s internal antenna, making such an antenna a very worthwhile piece of work whether you’re making a fixed link or indulging in a bit of casual wardriving.

The tools mentioned here will make helical antennas a snap, but this isn’t the first time we’ve touched on the subject.

29 thoughts on “Field Testing A Home Made WiFi Antenna

  1. The cheapest way I’ve heard of is to use an old satellite dish and place the WiFi antenna in the focal point of the dish, and odd as it may look the dish is pointing towards the ground (because it is usually points horizontal to receive signals from the sky above). Also works for cellular/mobile phone frequencies if you point it towards a base station.

      1. I still don’t get why people use those Wi-Fi USB dongles, sure PCI-E is expensive for some reason, but MiniPCI-E -> PCI-E adapter cost like 1-2$ same goes for MiniPCI-E Wi-Fi cards.

          1. If you don’t care about latency, stability and cable over 1 meter requirement high wizardry level to make it work on most hardware, otherwise cheap AP with Ethernet is your friend or just get cheap low loss cable(just check if spec are not fake before buying) sometime RG-58/U can do the trick, if cable not too long.

        1. A Parabolic Reflector Antenna has a unique property that the distance from the focal point to any point on the dish to a plane parallel to the dish is the exact same distance. This property means that the frequency as long as it is about a gigahertz or above does not really matter.

          At lower frequencies RF the dish would need to be larger (1 GHz have a wavelength of 30 cm ; ~1 foot)

        2. Gain ( beam width ) is related yo aperture ( dish size ) / wave length .
          So yes the dish will work for both. Just that it works better at higher frequencies.

          Sorry I’m to lazy to go look up the formula. :-)

    1. Care to elaborate?

      I though 2.4 GHz is a fair game and he does not use any additional amplifier. Or do you mean that he possibly exceeded maximum allowed EIRP? Or is there a problem with the polarization?

    2. Weirdly, it is, if you hold a HAM license

      Have a look at an oddly titled book called High Speed Multimedia for Amateur Radio

      So far as I’m aware, it’s never been updated so a LOT of the software links in it are dead, but if you spend some time, the code and necessary data can be found on the modern web.

      1. It’s only ham legal if you operate on the few wi fi frequencies that fall into the 2.4 GHz shared WiFi band, you ID properly, and don’t use the service for commercial purposes. See FCC Part 97 for the amateur service rules in the US.

  2. For ISM systems, the rules state that if you increase the Tx antenna’s gain by X dB, then you are required to reduce the Tx power by X dB. That ensures the received power at somebody else’s antenna does not increase.

    There is no such restriction on Rx antennas.

    Increasing gain can still help in terms of reducing the Tx power consumption and by reducing interference at the Rx.

    1. Technically it comes down to what was approved under type testing. You as a consumer are using a manufacturer’s FCC license for a piece of equipment. It must go through type approval with the antenna and cables to be used. Using it outside of approved configurations nullifies the license and you can be held responsible for it not conforming to FCC rules.

    2. Agreed this should be addressed, but just want to point out max power is 1 watt (30dB), but max EIRP is 4 watts (36dB). So everyone can benefit from a good antenna.

      You only have to turn down the power if your gain is over 6dB and if you are transmitting at full power. Most devices only transmit about half that, so if you are starting from only 25dBm, going off of the linked website, I saw a default of 11dBi, so you wouldn’t have to turn it down at all.

      1. Oops, it looks like I was under informed, so for everyone else:

        When used in a fixed point manner, in the 2.4 GHz band you can increase the antenna gain to get an EIRP above 36 dB but for every 3dBi increase of antenna gain you must reduce the transmit power by 1 dBm.

        So if you have a 12dBi antenna, then you can transmit up to 28dBm or 630mW (for a total of 40dB).

  3. Beside lack of proper MIMO(with arguable make it not so useful for your average person), aren’t skin effect gonna destroy efficiency?
    Why he remove insulator from wire if he gonna use it outdoor?
    Why make multiple antennas over couple dual-frequency or one quad-frequency?
    Also why 2.4GHz over 1GHz(outside of retrofitting existing system), he is even have 1GHz one, 802.11af 1-4 channels adapter cost like 5-$20 depend on manufacturer.
    For longer distance there is DASH7.

  4. You may be surprised how much gain you get from a simple [parabolically] curved piece of aluminum foil placed tangentially to a common WiFi router duckie coil antenna.

    1. beer can linear parabolic reflector, the first step everyone must try for icreasing the link quality before attempting to build actual custom antennas.

      building custom helical and quadrifilar antennas is nice and good but first you should get your feet wet with simple signal directing elements.

    1. Openwrt on dual antenna Linksys routers can be set to one antenna connector for transmit and one for receive. Of you turn down transmit power you are mostly legal depending on country and rules. Using open source router software you can also change ACK or acknowledge timeouts allowing links to work over crazy ranges. 5GHz links are far better and antenna’s are relatively smaller.

  5. Even a simple side-fired cantenna — if you can still find a metal coffee can — can greatly increase range. Built a pair of those when I needed to get a signal from one end of a hotel to the other and their internal network couldn’t handle it.

    1. I live in the Ozarks of Missouri and have no Wi-Fi. When we moved here I was getting -110 dbm on my cell signal. I installed a High Boost 4K system with a yagi antenna and my dbm now is anywhere from -95 to 100 Depending on time of day. I wish I could lock my band on 12 because that’s my strongest band. I used to be able to do it with Samsung band select but that app was discontinued. So I’ve reduced the Boost from band too and five in the hopes of just getting band 12, but it’s still bounces from band 5 and band 12.
      So, my question is, do any of you smart and knowledgeable people out there have any ideas to help me receive a better signal.

      Thank you..!

  6. The concept of long range is simple. More gain=more directional. The longest range systems use parabolic reflectors. They also must be aimed precisely so fixed locations or tracking is required. The helical used here is less directional so a little more tolerant of aim. One problem with high gain wifi is that it generally requires cleat line of sight. High gain antennas also have high rejection of signals not within the beam pattern.

  7. The ultimate limits of wifi are atmospheric losses which add up to eventually put you below the noise floor. The noise floor of wifi is fairly high due to the amount of interference on that band.

  8. You may technically violate the regulations on EIRP but in reality you are less likely to interfere with anyone elses services because you are more directional and unless they are within you frenel zone they would not know you were there. For highly directional antennas this is generally directly in line of sight of your antenna.

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