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Antennas for weak, scattered signal caused by rain and wind over 4+ miles of water.

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  • Antennas for weak, scattered signal caused by rain and wind over 4+ miles of water.

    I’ve been a CLEAR (wire) customer since 2007. Have lived in 2 locations, both have had marginal reception…..so dodgey that Clear reps suggested that I quit their service! Currently the signal from the tower travels 4.6 miles across the water (actual distance over water is 4.0 miles), over an 80 foot bluff, through trees and between houses to the Series M modem sitting in a 16” stainless bowl at a 45 deg angle atop the 4runner in my carport. On a day that’s calm and clear it gets 4 bars (lights) at best, but usually 3 bars. The problem is when its windy or raining or both there is enough interference from waves , wet flailing evergreen trees and falling rain that the signal becomes too weak or completely lost. The rumors are true, it rains a lot in the northwest! Tonight wind from S at 25 - 35mph, no rain, Series ‘M’ modem at 2 - 3 bars, RSSI = -77 to -87dBm, CINR = 7 dB to 17 dB.
    Later on a nice, clear day …. Wind from NW at 5 mph, modem at 4 bars, CINR = 17 to 20dB, RSSI = -78 dBm.
    Now I’m ready to move beyond salad bowl technology and install real antennas. I’m getting a Clear Series G modem WIXB-175 that will be hooked up with two antennas to take advantage of MIMO capability. The Primary will be up a large cedar tree, with LOS, aimed at the tower (panel, yagi or parabolic, Or? ) on a 30 or 40 ft LMR400 cable. The Secondary antenna (omni-directional?) will be under the carport eave (Not LOS) on a 10 ft cable. Will an omni antenna work well if installed horizontally?
    Are the internal wires from the antennas, the pigtails, shielded? Would you advise male N connectors on the cable ends since the pigtails and antennas seem to be female N’s ? Lightning protection sounds like a good idea… gas charged, 6Ghz? Which antenna(s) is best for “scattered” signal situation as in rain and water wave action? What CINR dB will CLEAR Wimax allow their customers to have? Or is it the FCC? Is there a way to add a switch or limiter to a cable to detune the system during nice weather? At what dB does my system start robbing signal from my neighbors? Is there a way to find out where the nearest CLEAR customers are?

    Please advise on which antennas to use. Thanks.

  • #2
    I’ve been a CLEAR (wire) customer since 2007. Have lived in 2 locations, both have had marginal reception…..so dodgey that Clear reps suggested that I quit their service! Currently the signal from the tower travels 4.6 miles across the water (actual distance over water is 4.0 miles), over an 80 foot bluff, through trees and between houses to the Series M modem sitting in a 16” stainless bowl at a 45 deg angle atop the 4runner in my carport. On a day that’s calm and clear it gets 4 bars (lights) at best, but usually 3 bars. The problem is when its windy or raining or both there is enough interference from waves , wet flailing evergreen trees and falling rain that the signal becomes too weak or completely lost. The rumors are true, it rains a lot in the northwest! Tonight wind from S at 25 - 35mph, no rain, Series ‘M’ modem at 2 - 3 bars, RSSI = -77 to -87dBm, CINR = 7 dB to 17 dB.
    Very nice summary of your RF environment. A few points. Typically the best performance you can expect from a high gain roof mounted wimax antenna is as good as you would get if you had your modem on the roof. I.e. the main purpose of these antennas are to overcome indoor coverage issues and not really to extend coverage - the reason is quite simply that the amount of additional gain that these antennas offer is not enough to boost an extremely weak signal and RF signals attenuate at an inverse-squared rate with distance. In other techonologies such as cellular/PCS/LTE we are able to use an amplifier/repeater that has a better receiver sensitivity (can pick up much weaker signals) and much higher (and variable gain) to pick up weak signals from much further away.

    You are correct in associating the rain to poor RF reception. You are also correct in identifying the bad effects of a water body to signal propagation. You really can't do much about this sadly. However, the RF shielding effect of the house structure which would get worse when damp would be mitigated by a roof-mount antenna and you may be able to play around with the antenna orientation/tilt to reduce the effect of the body of water.

    I’m getting a Clear Series G modem WIXB-175 that will be hooked up with two antennas to take advantage of MIMO capability. The Primary will be up a large cedar tree, with LOS, aimed at the tower (panel, yagi or parabolic, Or? ) on a 30 or 40 ft LMR400 cable. The Secondary antenna (omni-directional?) will be under the carport eave (Not LOS) on a 10 ft cable.
    You can get this from this kit: http://www.rfwel.com/shop/4G-USB-Mod...tenna-Kit.html. Please dont forget lightning protection.

    Will an omni antenna work well if installed horizontally?
    Typically not - although in a rich multipath-fading environment (where there's lots of obstructions between the base-station antenna and the client device) you will see less effect on vertical vs horizontal placement. Remember that a high gain omni antenna has a very small elevation (vertical) beamwidth. For example our 12dBi WiMax omni has just a 9 degree elevation beamwidth (360 degree azimuthal/horizontal beamwidth). So if you were to mount it horizontally you will miss out from capturing a lot of RX signal and your TX signal propagation will also be limited.

    Are the internal wires from the antennas, the pigtails, shielded?
    Note quite clear on this question. I'm assuming you mean UV shielded vs. Electrically shielded? The pigtail and LMR-400 is a coaxial cable so yes this they are electrically shielded by design. Clearly the pigtail would not be mounting outdoors so no need to worry about UV shielding but the LMR400 is UV stable. These outdoor antenna kits work just fine outdoors in standard (non-hazardous) environments.

    Would you advise male N connectors on the cable ends since the pigtails and antennas seem to be female N’s ?
    N-Male is the most common cable type. Most pigtails are either N-female or FME-Male. If FME-Male we provide an N-Female/FME-female adapter as part of the kit. So pretty much the kit provides everything you need to set it up (apart from the antenna mast but you can add that as well e.g. J-Pipe).

    Lightning protection sounds like a good idea… gas charged, 6Ghz? Which antenna(s) is best for “scattered” signal situation as in rain and water wave action?
    . Yes lightning protection is a VERY good idea. Make sure to correctly ground it though otherwise it would be a waste of time. Can't do much with rain fading. The best you can do is exactly what you propose i.e. have both antennas to take advantage of MIMO spatial diversity (i.e. the modem is able to use signals arriving at it from different paths to extract channel information and use this channel information to correct bit errors - so in effect help with speed). You are also correct in your goal to separate the main antenna from the aux antenna as much as possible which enhances the MIMO performance advantage.

    What CINR dB will CLEAR Wimax allow their customers to have? Or is it the FCC?
    You cannot do much to affect CINR though. CINR being the Carrier-to-interference-plus-noise-ratio. You can improve your carrier signal (with the high gain antenna) but sometimes this also increases the interference noise power which doesn't change the CINR. Sometimes by having a directional antenna such as the 18dBi 2.5-2.7GHz panel antenna, you may improve the CINR because if the interferer happens to be outside the beamwidth of the antenna (away from the main lobe) then you will not pick up much of it.

    Is there a way to add a switch or limiter to a cable to detune the system during nice weather? At what dB does my system start robbing signal from my neighbors? Is there a way to find out where the nearest CLEAR customers are?
    In general you would want to orient/place the antennas for maximum RSS in good weather and this should be the optimal placement even for inclement weather. Because these antennas are passive and you have relatively long coax runs that further attenuates the signal you typically are well within the EIRP limits so you need not worry about receiver desensitization and such (i.e. your strong transmitter or strong EIRP affecting neighbors' modems). Particularly because you plan to use a directional antenna with LOS to the tower. Not sure if CLEAR can tell you the user density or geographic distribution, and even if they did, not sure how you could use this information because your goal would be to orient the antennas to the direction of maximum RSS anyway.

    Here is a generic drawing on what you might end up with: http://www.rfwel.com/support/tech-dr...ENERIC_USB.pdf

    Hope this answers your questions. I typed this pretty fast so do let me know if you catch an error or not clear about anything.
    KF7RCQ

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    • #3
      Here's a question i'd like to know the answer to before I begin purchasing antennas.

      Could a Parabolic be a good choice for the LOS location? I'm thinking it covers more physical space than a panel and would therefore pick up more of the scattered signal.... or is there more to it than this? Noticed that its RF range is wider ... 2.3-2.7Ghz rather than 2.5-2.7....does this allow more interference and how much effect will that have on reception?
      With the 24dB Parabolic at the LOS location could the NLOS location then use a less powerful dB omnidirectional ? Such as the 7 or 8dB omni?

      Well, after reading this; http://forum.mikrotik.com/viewtopic.php?f=2&t=53244
      I believe I'll stick with a panel because of the scattered signal. If anyone has an opinion on any of my questions... i'd like to hear 'em.

      Thanks, Tree Hugger
      Last edited by Tree Hugger; 02-18-2012, 01:06 AM.

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      • #4
        Read that post and most of that the discussion doesn't make sense to me ... one cannot just arbitrarily say that one is better than the other. In fact radiation surface area is irrelevant on it's own - you pretty much have to compare the spec's side-by-side and depending on your specific application determine which spec's are most critical.

        Examples:
        ---------
        1. For long distance links with a clear RF line-of-sight LOS (which means both an optical LOS and a Fresnel Zone clearance) you might want a narrow beamwidth, very high gain and good front-to-back (F2B) ratio.

        Because you might not get all you decide which is the most important. E.g. if alignment is an issue you might want to widen the beamwidth. If you have co-located transmitters on the tower you might want a higher F2B.

        2. For MIMO performance you want the paths to be as uncorrelated as possible (more technically you want the channel matrix to have the lowest rank possible). This means you need to tailor your beamwidths and F2B to capture the most area while leading to as little correlation as possible.

        3. Other environmental facts determine whether a panel will work better than a grid e.g. wind loading factor, ice buildup, ease of mounting/installation, antenna alignment etc. The key is to look at spec's side-by-side --- a very good panel could beat a dish or grid antenna anytime just depends on the specs.

        4. Interference is also a concern. for example our 2.5GHz 24dBi grid antennas actually extend to cover 2.4GHz ISM. This wide bandwidth could mean more adjacent channel interference degrading CINR.

        5. Physical size is also important especially when mounting area is constrained --- you need to provide a larger clearance area.

        There could be a lot more reasons just came up with these quickly. Panels are much more popular for non-professional installations - the price/performance ratio usually is unbeatable.
        KF7RCQ

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