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Nomadic Ethernet Bridge Problem

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  • Nomadic Ethernet Bridge Problem

    I'm a system integrator working on a project for an end user. The application is to create a wireless Ethernet link from a TV studio to a broadcast truck. The range required is 10 miles, and the bandwidth requirement is 20 Mbps (from the truck to the studio). The studio will have a 75 ft antenna, and the truck will have a 30 ft mast. The entire terrain is very flat. I am looking at solutions from Redline, Trango, and Vcom. Can anyone recommend another company? I am toying with the idea of using 3 radios at the studio connected to 3 sector antennas to increase range, but obviously this will increase cost. One company suggested this as an alternative to an Omni antenna at the studio. I was told by this company that I could only get about a mile, line of sight range from an Omni antenna, while another company quoted a 10 mile range. Does anyone have experience with Omnidirectional antennas that could give me some advice? Do I really need to go with sector antennas?

    Any experience would be much appreciated.

  • #2
    one mile vs. ten miles is a big difference!

    The simple idea is that nobody can tell you definitively simply from the information on this post. How you determine this is by doing an RF link-budget analysis. I.e. What is the gain of the omni-directional antenna, link distance, fresnel zone clearance, terrain, receive antenna type, type of modulation used, and fade margin desired. Luckily most radio vendors have their proprietary link analysis calculators that allow you to plug in what the environment is, what type of antennas you are using (if the radio doesn't already have integrated antennas), link distance, and what reliability you need at what speed etc etc etc and they tell you if this is doable.

    So in short you cannot answer this question generally.

    But i agree with whoever told you that for such long range high speed links you almost always use high gain directional panels or dish antennas. So I like the suggestion to use 3 120 degree sectors instead of the omni. You may or may not need to have 3 separate radios.

    Our primary partner with links at this distance is Proxim Wireless. Check out for example their Tsunami QB series point-to-point radios. Once you sign up as a partner they will provide their link budget tools for free and this will give you are very good idea on what radios and antenna configurations you can use.

    So just to clarify whether an omni will work or not will depend on the RF link budget .You start with what the transmit power is which is determined by the radio you pick (pretty much limited by the FCC for the particular frequency band used), what the transmit antenna is (if an omni what the gain is which determines the EIRP- effective isotropic radiated power), then you determine what the path loss is (which depends on the link distance, type of terrain, type of environment e.g. rainy, dry, urban, canyons etc - the link calculator will figure out what the path loss is when you enter this), what the receive antenna gain is, and finally what the receiver sensitivity is (which depends on the radio - receiver sensitivity is the minimum amount of signal required - or SNR - to correctly receive signal with a certain modulation). Other factors come into play such as the modulation used, amount of error correction etc But all these are radio specific and the link calculators take care of that. As part of the link budget you also have to leave some margin (called fade margin) which determines your reliability --- to figure this out you ask your client what's the worst that will happen if they dont get their 20mbps or if they lose their signal completely. If it's a critical link that they can't afford to go down say for more than 1 minute per year (and we have done some high critical wireless video links) then you allow plenty of fade margin and maybe even use redundancy - which further limits what choice of antenna you can pick. Remember also that frequency is critical to the path loss and link budget calculation. If you need unlicensed frequencies then you are looking at 2.4GHz or 5.8GHz. 2.4GHz tends to be quite noisy so 5GHz may work better at this distance.

    Hope this answers your question and I didnt just make this more confusing .
    KF7RCQ

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