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  #1 (permalink)  
Old 01-24-2008, 07:17 PM
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Default high gain antennas! so what's the catch???

hi

i dunno guy
the entire thing seems to be a bunch of *BS*
am using a us robotics 9108
and it got originally a 2dbi omnidirectional antenna
i purchased a merlin 9dbi (this thing is tall )
but beleive it or not
it hasn't increased sinal quality not a bit!
in best cases perhaps only less than 10%!!!!
even in terms od dbi
i got no difference

so what's up!!??

any ideas??
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  #2 (permalink)  
Old 01-25-2008, 01:36 PM
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Do you have a web site link for the antenna?
What is "sinal quality"? Do you mean "signal strength" or "Link quality"?
Do you have any before and after figures?
How far away from the router are you when you do the test and are there any obstructions between you and the router?e.g. concrete walls.
If your "merlin" is another omni then increasing the gain reduces the vertical beamwidth, some mfr's quote 25 degrees for a 9dB omni, so areas that were once able to receive the signal may not be able to do so now. If your router is placed high up, bedroom, then it may not be seen in some areas on the ground floor and vice versa.
Link quality will not necessarily improve with a higher gain antenna on your router as communication is a 2 way operation. Your router may be able to "shout" to your wireless card but unless it also has had an increase in gain to "shout back" you will not see much of an improvement.
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Old 01-25-2008, 03:14 PM
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Quote:
Originally Posted by Rob02 View Post
Do you have a web site link for the antenna?
http://merlin-me.com/

What is "sinal quality"? Do you mean "signal strength" or "Link quality"?
I meant the signal strength

Do you have any before and after figures?
mmm not sure what u mean, but i dont think so!

How far away from the router are you when you do the test and are there any obstructions between you and the router?e.g. concrete walls.
am less than 10 meters far, that's it, yes there are 2 or 3 walls blocking, am not sure, because the route is at an edge of a room door and haven't passed te door, so probably the edge is considred an obstacle...
no fish tanks, and the router is 2-3 meters high...


If your "merlin" is another omni then increasing the gain reduces the vertical beamwidth, some mfr's quote 25 degrees for a 9dB omni, so areas that were once able to receive the signal may not be able to do so now. If your router is placed high up, bedroom, then it may not be seen in some areas on the ground floor and vice versa.
Link quality will not necessarily improve with a higher gain antenna on your router as communication is a 2 way operation. Your router may be able to "shout" to your wireless card but unless it also has had an increase in gain to "shout back" you will not see much of an improvement.

yes it is an omni antenna, and the router is 2-3 m high, so when u say "increasing the gain reduces the vertical beamwidth" do u suggest that i lower the router to 1.5-2 m high? or at the same level of the laptop?? also plz note that both the router "USR 9108" and the pc card are USR and of the same recommended compatible series by US Robotics,,,

And are u saying that it useless to increase the gain of the antenna only and not the pc card, or the laptop's built in wireless adapter?? are u saying that?? coz iheared it before but got something to say about it

thanks a lot mate
amwaiting for ur reply
cheers
^^^
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Old 01-25-2008, 03:16 PM
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also note that it is not a cheap model
it costed me 115 AED
that's 31 USD
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Old 01-26-2008, 07:56 AM
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Quote:
Originally Posted by aliitp View Post
^^^
[http://merlin-me.com/]
They don't seem to provide a data sheet for the antenna which is not a good start. Do you connect the antenna directly to the USR router or is it on a stand and you connect by cable? If cable how long is it and do you know it's losses?

[Do you have any before and after figures?
mmm not sure what u mean, but i dont think so]

Did you record the "Signal Strength" with the original antenna and then record it with the new antenna.
How are you measuring signal strength? Most wireless cards are not very accurate at doing this. Received Signal Strength Indication - Wikipedia, the free encyclopedia

[there are 2 or 3 walls blocking, am not sure, because the route is at an edge of a room door and haven't passed the door, so probably the edge is considered an obstacle..]
18inch concrete walls attenuate the signal by 18dB and if you have several walls that is a lot of attenuation. NB if you are at an angle to the router the wall thickness increases as will the attenuation.
Wi-Fi - Wireless Wiki - a Wikia wiki

What are the rules regarding max EIRP for 2.4GHz wifi in the UAE?
In the UK the max eirp is 100mw which is 20dBm and according to the data sheet for the USR9108 it has a 19.8dBm output and replacing the antenna with a 9dB one would place it well over the allowable limit.

[And are u saying that it useless to increase the gain of the antenna only and not the pc card, or the laptop's built in wireless adapter?? are u saying that??]

If you wish to improve link quality and try and increase data throughput then yes.
Try playing with different Tx and Rx antenna gains in a link calculator.
Wireless Network Link Analysis
Link Calculator : Wifi Extreme, Outdoor Wireless Systems

Last edited by Rob02; 01-26-2008 at 08:21 AM..
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Old 01-26-2008, 08:02 AM
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Quote:
Originally Posted by Rob02 View Post
[http://merlin-me.com/]
They don't seem to provide a data sheet for the antenna which is not a good start. Do you connect the antenna directly to the USR router or is it on a stand and you connect by cable? If cable how long is it and do you know it's losses?

[Do you have any before and after figures?
mmm not sure what u mean, but i dont think so]

Did you record the "Signal Strength" with the original antenna and then record it with the new antenna.

[there are 2 or 3 walls blocking, am not sure, because the route is at an edge of a room door and haven't passed te door, so probably the edge is considred an obstacle..]
yes they do not provide that
the antenna is directly connectable to the router
i haven't got any figures but i tested the strength of the signal with the 2 antennas, but they haven't improved a bit!!!!
this really is strange! are high gain antennas suposed to solve problems in case of low signals even if users are behind obstacles even behind walls or they only provide extra range??
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Old 01-26-2008, 01:29 PM
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Wifi does not like obstacles as they attenuate the signal and can cause multipath reflections which affect the signal. Most high gain antennas were used outdoors or large open indoor areas to increase the range of the signal and also to compensate for any cable loss between the wireless and antenna.
As I said earlier that using a 9dB antenna on a USR9108 in the UK would exceed the allowed eirp level, however if I wished to extend the range of my wifi network into the garden I could use a length of coax with a 7dB loss to an external 9dB antenna and still remain legal.
9108 has about 20dBm op with a 2dBi antenna so
20-2(2dB antenna) + 9dB(9dBi antenna) -7dB(cable loss)= 20dBm
Still legal.

Using high gain omni antenna in a house can be very much an experiment and sometimes it is easier to move the router to a different location within the house to obtain a better signal. If the router is in the corner of the house and cannot be moved it is sometimes better to use a sector antenna or a flat panel antenna.

When buying an antenna it is worth checking to see if they have a data sheet.e.g
9dBi Omni
http://www.hyperlinktech.com/web/pdf/hg2409rd-rtp.pdf
8dBi Omni Outdoor
http://www.hyperlinktech.com/web/pdf/hg2408u.pdf
8dBi Flat
http://www.hyperlinktech.com/web/pdf/hg2409p.pdf
Notice the difference in antenna gain patterns and vertical beamwidth.
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Old 01-26-2008, 03:35 PM
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Quote:
Originally Posted by Rob02 View Post
Wifi does not like obstacles as they attenuate the signal and can cause multipath reflections which affect the signal. Most high gain antennas were used outdoors or large open indoor areas to increase the range of the signal and also to compensate for any cable loss between the wireless and antenna.
As I said earlier that using a 9dB antenna on a USR9108 in the UK would exceed the allowed eirp level, however if I wished to extend the range of my wifi network into the garden I could use a length of coax with a 7dB loss to an external 9dB antenna and still remain legal.
9108 has about 20dBm op with a 2dBi antenna so
20-2(2dB antenna) + 9dB(9dBi antenna) -7dB(cable loss)= 20dBm
Still legal.

Using high gain omni antenna in a house can be very much an experiment and sometimes it is easier to move the router to a different location within the house to obtain a better signal. If the router is in the corner of the house and cannot be moved it is sometimes better to use a sector antenna or a flat panel antenna.

When buying an antenna it is worth checking to see if they have a data sheet.e.g
9dBi Omni
http://www.hyperlinktech.com/web/pdf/hg2409rd-rtp.pdf
8dBi Omni Outdoor
http://www.hyperlinktech.com/web/pdf/hg2408u.pdf
8dBi Flat
http://www.hyperlinktech.com/web/pdf/hg2409p.pdf
Notice the difference in antenna gain patterns and vertical beamwidth.
dear no lemitations are applied here
besides i dont know what u mean by saying "use a length of coax with a 7dB loss to an external 9dB antenna"!

so it's true that the 9dbi or even 15dbi antenna is no good and will make no difference because i still have got obstacles, is that true? coz if so ill just go ahead and return this piece of trash coz this is getting really annoying!! btw i bought a 6dbi before ((US ROBOTICS ANTENNA !!)) and haven't found any difference so i returned it...
thx pal i appreciate your help
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Old 01-27-2008, 09:20 AM
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[dear no lemitations are applied here]

Just because it is unlicensed it does not mean it is unregulated. I think you will find that the UAE is part of EMEA and there is a limit on power output.
e.g. http://www.cisco.com/en/US/docs/wire...e/bkscgaxa.pdf

[besides i dont know what u mean by saying "use a length of coax with a 7dB loss to an external 9dB antenna"!]
If I was going to place the antenna outside the house I would leave the router inside the house and connect it's antenna port by a long length of coax cable to the the now external antenna. Different types of coax attenuate the signal by varying amounts depending on it's construction and the frequency used.
Try the calculator here:-
Attenuation & Power Handling Calculator

Frequency= 2.4GHz
60ft LMR-100A gives 23.3dB's attenuation
60ft LMR-200 gives 9.9dB's attenuation
60ft LMR-400 gives 4.0dB's attenuation

Last edited by Rob02; 01-27-2008 at 09:36 AM..
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Old 01-27-2008, 11:31 AM
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Quote:
Originally Posted by Rob02 View Post
[dear no lemitations are applied here]

Just because it is unlicensed it does not mean it is unregulated. I think you will find that the UAE is part of EMEA and there is a limit on power output.
e.g. http://www.cisco.com/en/US/docs/wire...e/bkscgaxa.pdf

[besides i dont know what u mean by saying "use a length of coax with a 7dB loss to an external 9dB antenna"!]
If I was going to place the antenna outside the house I would leave the router inside the house and connect it's antenna port by a long length of coax cable to the the now external antenna. Different types of coax attenuate the signal by varying amounts depending on it's construction and the frequency used.
Try the calculator here:-
Attenuation & Power Handling Calculator

Frequency= 2.4GHz
60ft LMR-100A gives 23.3dB's attenuation
60ft LMR-200 gives 9.9dB's attenuation
60ft LMR-400 gives 4.0dB's attenuation
ok i got it regarding the coax cable, and the regulation, but regulation are not the issue it the time being, not for us
so in conclusion, is there is anything i can do to resolve this issue? (btw now am working on the 2dbi antenna and it's fine) or shall i return it back to the store i bought it from???
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Old 01-29-2008, 01:39 PM
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ok i got it regarding the coax cable, and the regulation, but regulation are not the issue it the time being, not for us
so in conclusion, is there is anything i can do to resolve this issue? (btw now am working on the 2dbi antenna and it's fine) or shall i return it back to the store i bought it from???
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  #12 (permalink)  
Old 01-30-2008, 06:19 AM
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Link quality will not necessarily improve with a higher gain antenna on your router as communication is a 2 way operation. Your router may be able to "shout" to your wireless card but unless it also has had an increase in gain to "shout back" you will not see much of an improvement.
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Old 03-05-2008, 02:08 PM
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you have to look at the cable and connector loss and subtract it from the gain.

Because of this in practice it does not make sence to use a external antenna / pigtail with less than 8dBi gain.

a 7dBi with attached pigtail will offer a good bost over a stock 3dBi
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