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I'm planning on using 2 receivers that operate on the same frequency. So there's no confusion I'm talking about WiFi signals (but I'm trying to do some cool amateur radio stuff with it!) so the frequency is 2.4GHz. One of the main things I'm working on is building a nice big antenna (high gain) to be able to have a usable signal over more than 10s of meters. Now ideally, since these two receivers will have the same frequency, I could place both receivers at the focal point of the antenna and have the one dish with 2 receivers - but I'm worried that there will be a loss of signal since the antennas are blocking each other to some extent. Is this the case? I'm looking for an experienced person to give me there best guess really!

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  • $\begingroup$ Beware of small diameter coax at 2.4Ghz. It seems quite common with wifi gear. $\endgroup$ – Paul Jan 1 '14 at 3:58
  • $\begingroup$ You say they are receivers, but then you mention these are wifi signals. Are you certain that they are only receiving, and neither are transmitting at all? The wifi transmission is only one way, and the antennas never transmit? $\endgroup$ – Adam Davis Jan 1 '14 at 8:01
  • $\begingroup$ And what do you hope to accomplish with 2 receivers, on the same frequency, connected to coincident antennas? The interaction of these antennas aside, you are receiving the same information twice, so I don't see any point in it. $\endgroup$ – Phil Frost - W8II Jan 1 '14 at 13:18
  • $\begingroup$ OK. Mistake number one is that you're right I want to send and receive from the antennas (I'd split the problem into to, and forgot to step back). Wifi signals are all in the 2.4GHz range, they antennas will be connecting to different sources! $\endgroup$ – FraserOfSmeg Jan 2 '14 at 20:30
  • $\begingroup$ You still haven't described what you are trying to accomplish. $\endgroup$ – Phil Frost - W8II Jan 3 '14 at 20:53
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As your comment mentions, since you're transmitting also, you will have issues.

Placing two antennas within ~1/2 wavelength of each other will cause them to inductively couple - effectively connecting themselves to each other. This results in detuning both antennas, as well as the high power Tx RF getting routed back down the other antenna, possibly damaging the receiver. I did this once with 2m mobile rigs - I had my HT connected to a magmount placed too close to the antenna for my 50w mobile, resulting in a fried protection diode in the HT.

As others have asked, what is your goal in having two receivers? If you're trying to run two different networks, why not just overlay a virtual SSID on the same AP?

73 de KD8EVL

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  • Main factor for transmission distance is so-called effective heights of antennas on both sides. Basically it is about how high antennas are located - the higher is the better.

  • Another important factor is lack of obstacles in line of sight - hills, trees, buildings, etc.

  • Length/size of antenna elements is important only to extent you keep original antenna design. No special need to make it bigger.

  • At some height of antenna you will need protection from wind (well-engineered mechanical mount) and lightings (grounding within electric code rules) - both are safety protections and law-regulated across most of world.

  • If your antennas are directed, it is important you orient them on each other along direct visibility.

Your idea about two receivers is waste of time/effort/money - you can do even hundreds of meters without it, on basic equipment, if you keep rules above done. Area of radiocommunications (antennas, receivers, transmitters, etc) is well-studied during XX century due to high impact on military operations - it is unlikely that coolness of your idea makes something new.

You can rather spend some time experimenting in making your own antenna from Pringle chips can, so called Cantenna - it will be cheaper and have more impact. Reading books on topic in local library will give you even more boost.

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  • $\begingroup$ Hi there. I think you might have miss understood my question. I'm asking what negative effect might I experience when using 2 wireless antennas place side by side. It defiantly isn't a waste of time or money as it will allow me to connect to 2 different wireless routers with 100% uptime (as opposed to hoping between 2 using one antenna). I don't mean to be rude but it's not usually good practise to subjectively comment on the validity of a questioners project unless specifically asked for. Thanks for your input nevertheless. $\endgroup$ – FraserOfSmeg Jan 4 '14 at 4:14
  • $\begingroup$ @FraserOfSmeg so is your goal to have a redundant transceiver and antenna to improve availability? If so, you should put that in the question so people don't have to guess at your goals. $\endgroup$ – Phil Frost - W8II Jan 5 '14 at 16:48
  • $\begingroup$ My goal is to connect to two different wireless routers simultaneously. $\endgroup$ – FraserOfSmeg Jan 5 '14 at 18:52
  • $\begingroup$ Well... granted texts above, you try to achieve MIMO. Sad thing is, you don't grasp yet your challenges are not only limited to radio. To make it less pain on radio side, consider to equip your (PC,notebook, tablet) with MIMO card or dongle, and make sure your router (one router is enough, two ore more antennas) on other side is MIMO too. And re-read my answer above (minus brazen paragraphs) - what they teach radio guys first, if distance is main problem then there is nothing better than raise both antennas method. Here be dragons... $\endgroup$ – silpol Jan 6 '14 at 14:56
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You can vertically separate the two receiver vertically, one directly on top of the other. The transmitter are very ineffective at transmitting directly above or below. Almost all the power is horizontal to the antenna. The next thing is to also use the 5Ghz band 802.11N/AC of WIFI if possible on one of the routers to further reduce interference. If you have to use 2.4 802.11B/G for both you can manually pick two channels that are the farthest apart in frequency.

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