new 7dbi antennas, best tx power setting?

Discussion in 'Tomato Firmware' started by c_martini, Aug 5, 2008.

  1. c_martini

    c_martini Addicted to LI Member

    I have two questions for which the solutions for them may affect each other:

    I just received a pair of Linksys 7dbi high gain antennas and am going to replace the stock 2db ones on my wrt54gl. I was wondering what the optimal transmit power setting would be for these new antennas?

    At the moment, on the stock ones, I am only getting about a 40% signal strength from my pc which is located about 12 meters away (40ft) in another room. There are 2 walls in between. Tomato's device list page is reporting an rssi of -72dbm and a quality of 27 for that connection. The pc has a netgear wg311t wireless adaptor card fitted with a large 12db antenna. I don't know why the signal is this bad over such a short distance. I was careful to try and select a channel that was at least 4 away from the nearest strongest neighbour's (mine is channel 6 and my neighbour is using 11). I get frequent slowdowns, an erratic signal, jumping all over the place from about 1mb to about 48mb, and even disconnections to the point where the pc cannot reconnect and I have to hard reset the router. The signal strength of my neighbour's wireless router is much stronger despite being about the same distance away :confused:

    I even tried replacing the wireless adaptor card which only seemed to improve things marginally...

  2. asterger

    asterger Network Guru Member

    First off, a -72dbm RSSI with a 27 Quality is not a bad signal. Mine is only -69dbm and 29 Quality. The link is so stable, I update Tomato wirelessly from my laptop.

    I suspect part of your problem comes from using channel 6. Stay away from channels 1, 6 and 11. While these are preferred non-overlapping channels, channel 6 is the default for every Linksys router, with Channel 11 the default for all Netgear. Channel 1 is close to the band edge where other interfering devices live. If you have 802.11b interference on channel 6, try Tomato in mixed mode.

    Channel switching and examining RSSI, I've noted higher signal (less negative dbm) on higher channels. In my neighborhood, there are 3 users on 6 (1 of them 802.11b) with other users on 1, 10 and 11. While the RSSI of these signals are in the -90dbm range, I still selected unused channel 8 half way between channel 6 and channel 10. And like I said, my signal is quite stable.

    Moving away from channel 6 would be my first change.


    -- asterger
  3. c_martini

    c_martini Addicted to LI Member

    Intriguing suggestion. My router was at channel 11 by default. I live in the city and I had initially moved to channel 6 as my nearest neighbour with a very strong signal was at 11. There was another nearby strong wifi hot spot on channel 1. I read somewhere it was best to keep it set as far away from other neighbouring channels as possible. So since the neighbouring ones were at 1 and 11, 6 was my logical choice.

    I will however try using a higher channel between 6 and 11. Perhaps channel 8.

    I did install the new antennas but have only noticed a marginal improvement in signal strength from the pc wifi adaptor. I suspect it may be something on the pc end as my nokia internet tablet and my wifi enabled nokia n95 both report a very strong and improved signal from my router when used in the same area as the pc.

    Even despite adding a larger antenna to the Netgear card in the pc, I still have problems. I wonder if it could have something to do with the actual location of the antenna, which is connected directly to the card close to the floor, and as the computer has a tower case, the antenna sits against the casing, surrounded by the various cables and power leads. That places it about 5 feet lower in height than the level at which the router sits in the other room. I am wondering if it would make sense to add a cable between the wifi card and antenna so I could place it up higher and away from the pc

  4. Haakie

    Haakie Network Guru Member

    Yes, the location and angle of the antenna can improve your connection. That's the advantage of USB WiFi-card, you can move them around. But it's no holy grail. Try to borrow some gear somewhere first instead of buying.
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