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Will a Cyfre CA-819 cellular amplifier be a benefit to my performance?

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  • Will a Cyfre CA-819 cellular amplifier be a benefit to my performance?

    Ok, here's my situation. I'm running a Verizon/Novatel USB-727 EVDO data modem.

    My gear is:
    CradlePoint MBR1000 Router
    Omni external antenna - antenna gain 5dbi, system gain 10-15 db
    Linksys PAP2T - VOIP Adapter

    Modem readings from the router:
    My dbm without external antenna: -85dbm
    dbm with external antenna: -75dbm (nice improvement)
    Signal Strength with antenna peaks at 73% (would like to see better)
    Data speeds:
    Download: 700-1500kps
    Upload: 200-700kps
    Ping times: 90-200 - maxes at times to 325

    Now, to the point. With all of this, my intention is to improve my VOIP(internet phone) performance. My problem is sometimes echo and sometimes too much jitter (breaking up of voice).
    My first experience was a system called Magic Jack. Some of you might have heard of this - A USB device. The echo and jitter was horrible. I returned it.
    My current setup is the Linksys PAP2T using Callcentric as my service. The improvement by changing this setup only has been very positive. However, there is still periodic jitter, and bad weather doesn't help. I myself can handle momentary jitter now and then, but I'm married, and the little woman is impatient, and if she hears just one breakup it's done and buried. I guess some of you guys know the feeling. Your greatest test of salesmanship is convincing your wife.

    I'm really feeling I'm on to something here, and just a little tweaking can get me just right. I live in the mountains, and although I do have a direct line of sight to the towers (about 5-7 miles) , the leaves will be coming in soon, obstructing that view, and potentially dropping my performance.

    So, the question is - will an amplifier like the Cyfre CA-819 make a difference breaking through the various obstructions (trees, leaves) and improve my performance, momentary jitter, and ping times? If not, are there any suggestions?


  • #2
    I hear you on convincing the woman ... sometimes they don't get just how much you have labored to even get that far and how what you have so far is impressive in itself But you gotta love them ..... all they want is simply for the damn thing to work just like a PSTN line

    The RSS's (received signal strength) and RTT's (rount trip time) you are recording are actually pretty good (if they are consistent). You might actually be hitting the jitter and latency limits of EVDO RevA. Jitter is actually much harder to resolve since it's non-deterministic. Since EVDO has higher latency that DSL for example Jitter problems become more noticeable and more problematic.

    Unfortunately there's really nothing you can do if the problems you are experiencing are on the network side. If they are on the RF air interface between you and the BTS then it would depend on the nature of the problem. For example if the RF channel is such that you periodically experience fading including for example multipath fading which momentarily takes your RSS below the receiver sensitivity of your U727 then it's reasonable to assume that a radio with a better receiver sensitivity (in this case a cellular repeater like the Cyfre or Wilson) might help maintain connectivity during these deep fades. If on the other hand your problem is multi-user access such as if they are competing for the same RF spectrum it depends on how this plays out: On one hand having a powerful radiator does help (CDMA multiuser-access method is pseudonoise sequence codes that makes each user appear as noise to other users. A powerful radiator would tend to drown out others. Not a kind thing to do ) On the other hand though assuming that the power control on the amplifier is working ok and normalizing transmit power across users then you really do have to share the finite carrier channel capacity (evdo reva implements multi-user packets) which adds to higher latency but since user access is somewhat non-deterministic this leads to something worse that latency which is "latency-variation" aka jitter.

    So simple answer is "maybe". Probably not the answer your looking for . If your RSS is varying drastically with time and season then you have a good chance to optimize this. Even a higher gain 13dBi directional roof mount antenna (such as a Yagi antenna) might do the trick. If on the other hand what you report is consistent you probably would not get much better than this which means your limited by the network which means your S.O.L until they roll out L.T.E (or all your neighbors move out).

    Needless to say I'm assuming that you have already of course played with the settings in the Linksys PAP2 to optimize VOIP settings such as what codec to use what servers to use (your provider might have closer servers to you) etc etc. Not really an expert in VOIP but have seen where tweaking a few software settings can make a lot of difference.


    • #3
      voip over evdo ...

      One clarification i just noticed is that fading doenst really have to take you out of the receiver sensitivity region of the u727 it just had to decrease SNR such that protocol has to modify modulation and coding rate (EVDO RevA users AMC - adaptive modulation & coding) --- the effect of the amplifier is the same to improve SNR.

      Also if VZW is using 800MHz in your area then the leaves would not affect performance by that much since it appears your not that far from the tower anyway.


      • #4
        I didn't get a chance to thank you, Thuor. Too bad others didn't chime in as well so I could get more perspectives to resolve my situation. But, perhaps I couldn't ask for more than the info you offered. To be honest, your reply was a bit of a stretch on my intelligence. Fortunately I've been taught well to apply specific words mentioned in a sentence that I don't understand, to sentences mentioned before, making the sentence more understandable. Did that make sense? Anyway, I think I got most of what you're saying, less the acronyms. L.T.E.?

        You're right, from what you've said, I still don't know if an amplifier will suit my needs. For me, spending $200+ dollars on a maybe is just too much of a financial hardship to take a chance. I've already gone quite overboard in other equipment to take a chance on a maybe. It is so confusing because my readings do look pretty good for EVDO. However, the momentary slam of static and jitter, that can last for a good 3 sentences in conversation can be quite disheartening - for me and the other party I'm talking to. For some reason I'm just thinking an amplifier can distinguish these issues and quickly adjust to compensate. I think you're right about tweaking settings in the software. Callcentric has truly been great answering many of my questions, but I think I'm going to have to ask them to give me a little support with a product they didn't sell me. Although this might be something they might feel is not their responsibility, it is in their interest to help a bit because if I don't find a way to straighten this out, I might have to stop my research and ultimately stop my services with them. The good side to this is that their web site has some great info. They offer fairly detailed settings (in order to get the device to work with their service) for each VOIP adapter that they support. However, at the same time I can't help but feel maybe they've heard all this before and have options beyond the documented settings listed on their site.

        Quite frankly, I'm just too close to getting this equipment to utilizing my "best chance settings." Somehow, I just can't help put feel there must be a solution. I'm just a fraction away.

        Sorry if I'm babbling. Thanks again for your valued input.



        • #5
          I was following this post and planned to chime in but thuor pretty much covered main points. LTE is "Long Term Evolution" that verizon has committed to deploy as the next generation faster speed lower latency network.

          my parents back in india use vonage on ISP's that provide worse connection than i believe evdo reva and we were able to get quality to discernible levels by optimizing voip settings. we never did quite make it as good as landline but for the money we save were happy.