SNR and Signal dBm?

Discussion in 'Cisco/Linksys Wireless Routers' started by michsu, Dec 14, 2005.


can my dad get good connection at (-89+15) = -74 dBm

  1. Yes

  2. No

    0 vote(s)
  1. michsu

    michsu Network Guru Member


    I recently bought the Linksys SRX (WRT54GX v2) and had a signal of -30 dBm (about 3-5 feet away) ... I needed to increase the signal so my dad could use it on the other side of the house... since the SRX can hold 3 removeable antennas, I removed two of them and replaced one with (amp 500mw(BA24J) + 9dbi omnidirectional) and the other with a 9dbi omni-directional , the third one is still stock (don't know what to put there)... now my signal is increased from -30 dBm to -15 dBm (for 3-5 feet)... how can I improve it even farther? I think with 27dbm (amp) + 9dbi , I am at the FCC limit of 1 watt...

    How does -15 dBm compare with everyone else? In the other side of the house, I am getting -89 dBm (before extra installation of antennas and amp), so I'm assuming -89 + 15 = -74 dBm?? would that be a good signal (was "very low", 1 bar...) There is about 100 feet (+ 3 or 4 walls , how much does a wall decrease the dBm signal?) of distance between the router and the other side of the house I tried using a directional 15 dBi antenna (hawking), however, it still wouldn't break through to the other side... so I am stuck with the amp + omni antenna now...

    Can someone help me on any additional information? I'm wondering if I pushed it as far as I can already... is it for every 3dB increase (double distance), however, some websites say you need 9dB to get a good indoor "doubling".... so since I have +15 dBm now, then the signal improved "5x" 5 times theoretically... but in reality, probably 1.5 times +150% (15/9)...

  2. michsu

    michsu Network Guru Member


    :cheering: BUMP :cheering:
  3. Private-Cowboy

    Private-Cowboy Network Guru Member

    1.) +74dm is a "low" signal but will do. The speed will fall back but it does work without interuptions. Thing is, the signal is influenced by the weather too (mine was -66 yesterday evening and is -70 now with the only change being the weather) so you need a little bit of buffer.
    2.) Buy a directional antenna and aim it at the other PC. The gain will be way better then those omni antenna in that case. You can leave the other omni in Place.
    3.) Reduce the speed of the router, slower speed equals better signal. So when you can live with a net of maybe 10mbit you can set it down to say 24mbit and that will help the signal even more.
  4. michsu

    michsu Network Guru Member

    thanks for your help.. haha, you are the first to actually answer my question of whether or not -74 was good.. I know it is kind of low, and I did try a directional (hawking) 15dbi antenna, but it made no difference it seems like ... I don't think 15dbi antenna can crack through 4 walls + 100 ft... or maybe I hooked it wrong (but it is the same R-SMA connector like the omnis).. do you know how much 1dbi usually goes in feet? that way I can calculate if 15dbi is good enough... maybe more?... I assumed that it was enough...

  5. Private-Cowboy

    Private-Cowboy Network Guru Member

    Are you sure you fit the directional antenna tightly? You've to screw that R-SMA connector till it wont move any more. I've that with my omni antenne, if I dont screw it as tight as it gets the antenna offers no gain at all.

    Coming to the question of whether an antenna will be sufficient, well you'll never know really because the weather influences the signal pretty badly. My signal moves by +-2db just by the weather alone. Here's a pretty good article about antennas:

    What is wrong with having a signal around -70db? It will be ok most of the time, it will fallback to 36mbit most likely but who cares. That will be still a net rate of around 10mbit.

    You can use a booster instead an antenna, they will gain even more. Here's one from Hawking:

    And don't forget to play around with the antenna positions on both ends, I can get a 5db gain by that alone! So if you find that sweet spot and use a 9db gain antenna it will most likely make the distance and penetrate the walls.

    Or use a directional yagi antenna, they are made for long distance wifi and will easily reach thousands of feet and will easily be ok for your setup. They are a bit ugly though:
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