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what is the best clear modem and external antenna combo

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  • what is the best clear modem and external antenna combo

    I'm in a bad, to OK, reception area for Clear, in northern Vancouver, WA (across the river form Portland, OR). We have placed a CPEi 25725 in a plastic bin lined with aluminum foil (to turn it into a directional antenna and to keep it from over heating), but the reception is still mediocre (13-17db). I need to know what the best solution is. I'm still in the 2 week trial so we can easily switch modems if that is needed. I did see that the G-Series http://www.wirelessgoodness.com/2010...eries-g-modem/ clear modem has what looks like the ability to support a external antenna (at least the version shown does). I have access to the following

    the G-Series (same, but most likely a different hardware rev.)

    the M-Series (this is the one I have)

    or the regular Clear Modem

    http://www.techforless.com/cgi-bin/t...oogle_shopping

    Clear doesn't offer any help on the website as to which model number you are getting with each Series.

    I'm close the peak of a the biggest hill in the area but there are a lot of trees (pine manly). So i want to know what modem to get and what kind of antenna (mimo or directional). This will be placed on the roof so I will need a lot of wire to get up there. Currently it sits about 20-30 feet lower then it will on the roof

    I need to know what pigtail to get assuming that I go with the G series.
    I also want to have this help as many people as possible.

  • #2
    We have placed a CPEi 25725 in a plastic bin lined with aluminum foil (to turn it into a directional antenna and to keep it from over heating)
    This to me seems like it would do more bad than good. Essentially you would be putting the modem in a Faraday Cage and would shield any little RF from getting to the internal antennas. Unless i'm totally picturing this construction wrong?

    but the reception is still mediocre (13-17db)
    I assume this is CINR or is this Tx Power? What is your RSSI (it will be a negative number -xx dBm. Are you able to connect at all?

    Your best bet is to go with a modem that does have external antenna ports then attach low loss coaxial cables and high gain outdoor antennas. But first it's IMPORTANT to evaluate your outdoor signal to figure out if you are even a candidate for these outdoor booster setups. If your Received Signal Strength (RSS) is too weak outdoors at the location where you would potentially mount a high gain directional antenna then it would be a waste of time to get the antennas. A passive system such as adding antennas is primarily useful to overcome in-building coverage issues (i.e attenuation of the signal as it goes through the building structure). These systems are NOT to improve reception in an otherwise low-coverage area. Some times though if you have marginal coverage the extra directional gain of these antennas can improve performance significantly to provide a robust connection or to improve speed (since speed for Wimax highly depends on the RSS/CINR).

    Once you determine that you can pick up a decent signal outdoors check out: http://www.rfwel.com/4g-data/wimax-a...wimax_antennas for different style of outdoor antennas. Our most popular is the 16dBi panel antenna. Here is an example setup drawing for the Clear Sierra 250U or the Clear PXU1900: http://www.rfwel.com/support/tech-dr...ENERIC_USB.pdf. This drawing shows using an MBR1200 to convert WiMax but to LAN/WiFi so you can hook up multiple computers but other Cradlepoint routers can work well too such as the MBR1000 or the MBR900. This has worked very well for many people with poor in-building coverage.

    This CPE modems don't have an external antenna port so the only way round this is to open up the case and detach the internal antennas from the PCB and hook up a pigtail to connect to an external antenna. We don't recommend this. Here is a forum post on that: http://www.rfwel.com/forums/showthread.php?t=810

    Again, very important, remember if you have no signal around and within several 10's of feet outdoors from where you can mount these external antennas then even the most powerful antenna will not work for you. In this case you are at the mercy of Clear to enhance their coverage or for WiMax amplifier/repeaters to be available in the market.
    Last edited by thuor; 08-19-2010, 02:38 PM.
    KF7RCQ

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    • #3
      "This to me seems like it would do more bad than good. Essentially you would be putting the modem in a Faraday Cage and would shield any little RF from getting to the internal antennas. Unless i'm totally picturing this construction wrong?"

      The foil is just on the bottom and sides of the bin, the lid doesn't have any foil on it (its just there for protection form the elements). Also, the bin is on it's side and the modem is mounted in the side that is now its bottom.

      "I assume this is CINR or is this Tx Power? What is your RSSI (it will be a negative number -xx dBm. Are you able to connect at all?"

      These are my current stats:
      WiMAX CINR: 12 dB
      WiMAX RSSI: -70 dBm

      i've seen the CINR as high as 17 and the RSSI as low as -68

      Yes, I can connect, and I just ran a speed test from Speedtest.net and got 92ms ping, 0.30 Mb/s down and 0.38 Mb/s up. I've also seen them as high as 80ms ping, 1.50 Mb/s down and 0.48 Mb/s up. We are also on the lower plan (1.5 down and .5 up). And yes, I understand that we should get more speed just by getting the faster plan (which is something we are probably going to do anyway).

      We tried putting the modem on a window sill and it worked, just not very well. We got about 8-10 CINR. Obviously we can't keep the modem outside on a long term basis, but the reception is definitely better when it IS outside. With that having been said, do any of the current Clear modems support a external antenna assuming that I remove the internal and drill hole(s) for the wire to get out? We could go the Cradlepoint route, but i really don't want to.

      I read the post "External antenna for Clear CPE25150". First of all, which series is that? I can't seem to find any pictures or anything to help me figure out which one is which. Also you talk about soldering, which i know is a bad idea. But with the right pigtail and a G series modem I should be good, right? Because the only modding will be popping out the internal antenna, snapping in the pigtails and then drilling 1 or 2 holes for the wire to get out.

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      • #4
        Your CINR and RSSI is actually quite good vs what i have seen with people who have poor indoor coverage. You definitely can benefit from having a good outdoor antenna.

        You are right that the previous post jumbles up info from the Series G & Series M. The discussion regarding using that U.Fl pigtail pertains to Series G (the Gemtek WIXB-175) modems. The CPEi25150 is a Motorola CPE. Here is in image of the WIXB-175 PIFA printed antenna & PCB: http://www.rfwel.com/images/WIXB-175internal.jpg

        Remember though that the U.FL antenna posts that attaches the printed antennas to the PCB are not really designed for continuous removal/replacement. It also goes without saying that this mod voids the warranty (even if you don't drill into the case). Here is the pigtail: http://www.rfwel.com/shop/8-N-Female...e-Pigtail.html. This would attach directly to LMR400 N-Male/N-Male Cable.
        KF7RCQ

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        • #5
          Thanks for your help thuor! but just to clarify a few things, you are saying that I need a G series modem with a U.Fl pigtail (do I need 1 or 2?) What is the shortest length of LRM400 (and when does it start to drop of. You made it sound like it does drop off significantly at 20-30 feet? Is that what you are saying? But then that begs the question, why are there 100 foot leads of this stuff that you guys sell?) And do you still recommend that I get the 16dBi panel antenna?

          Also do I need 2 antennas or just one, and if I just get one, which port do I hook it up to?

          Are these pictures of the a G series a current iteration, or if not has there not been much change to what is shown?

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          • #6
            you are saying that I need a G series modem with a U.Fl pigtail (do I need 1 or 2?)
            Ideally you need two pigtails, two cables and two antennas. This is because WiMax protocol uses MIMO (Multi-Input, Multi-Output) antenna technology and MIMO signal processing. MIMO helps with performance improvement especially where there's lots of multipath fading due to obstructions between the WiMax BTS and the CPE antenna. In some cases, for example when you can get a clear line-of-sight to the WiMax tower, MIMO diversity and coding gain is not as big and in these cases having a single antenna is good enough. What we recommend is to start out with a single antenna and if your signal is just as good as having the modem outdoors then you are fine. If having the modem outdoors is still better than having it indoors with one outdoor antenna then this suggests that a 2nd antenna would help.

            What is the shortest length of LRM400 (and when does it start to drop of. You made it sound like it does drop off significantly at 20-30 feet?
            LMR400 has an attenuation of about 6.9dB/100ft at a center frequency of 2600MHz (recall Clear 4G WiMax operates at approx 2.5-2.7GHz). A 30ft run has a loss of about 2.1dB. The longer the run the more the loss so that's why we say you should keep this as short as practical. Notice that part of the reason that LMR400 is pricey is because it has such low attenuation at high frequency. If for example you attempted to use 195-series cable this would give you almost 20dB of loss per 100ft.

            You can have as short of a cable as you want. I think we stock from 2ft to 150ft. Above 150ft we recommend going to LMR-600 cable (4.5dB/100ft @ 2.6GHz).

            Since WiMax uses adaptive modulation, to determine what cable/antenna you need is actually quite simple if we know the receiver sensitivity required for the highest modulation mode. The highest modulation mode which is 64QAM with 5/6 FEC gives you the fastest speed. Not sure what exactly it is for the WIXB-175 but a good guess would be somewhere around -59 to -69dBm or better. If we even say it's -60dBm and your signal is currently -70dBm then you need a 10dB gain. If you start with a 16dBi antenna, have a 2dB cable loss and maybe 1dB connector losses, then your effective gain is 13dB which is better than your target gain (or said another way your signal would be about -57dBm). Note that you may not see this new RSSI reported precisely as this due to other reason but you still get the benefit of this extra gain - and an increase in effective isotropic radiated power (EIRP) on the transmit side.

            and if I just get one, which port do I hook it up to?
            Hook it to the primary antenna port labeled "ANT1" on the PCB.

            Are these pictures of the a G series a current iteration, or if not has there not been much change to what is shown?
            Not sure about this. I would imagine even if the layout changed it wouldn't be hard to spot the internal antenna connections.
            KF7RCQ

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            • #7
              Not lining up

              so I purchased the pigtail cable for the series g as well as the lmr m to m cable. Well guess what, its not lining up...Did I miss an extra part??? someone, help!!!

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