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Variating bitrate using directional antenna

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gauteoh

New Around Here
Hi snb forum :)

I am using a setup where I have a high gain directional antenna (max 27 dBm) pointed at a open wifi which I connect to. The antenna is bought from ebay and connected to a TP-link WA730 running openWRT LuCI.

The connection has variating bitrate, but most of the time it is good. The picture shows what I am talking about. Does anyone in here know how I can improve the connection and get rid of the sudden drops in bitrate?

When I mounted the antenna on the wall I made sure it had the best possible direction by checking the signal strength/noise levels. I appreciate all the help I can get.

Thanks!
 

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27dBi would be a dish, or a very large yagii. If it's small, or neither, then the 27 you cite as "dBm", is max power tolerated by the antenna. "dBm" is power, not gain. zero dBm is equal to 0.001 watt. On the log scale (RF is that way), 20dBm is 0.1 watt or 100milliwatts.
Antenna gain is measured (usually) in dBi (that's decibels relative to an ideal isotropic (spherical) antenna.

Please show us the make/model of the antenna. And the connecting coaxial cable, which MUST be short and/or large diameter (say, 1/2 in.) if more than a few inches long. This is to keep losses due to coax low.

Radiated power is transmitter power in dBm + antenna gain in dBi - coax loss.
Some antennas have negative gain - e.g., some in very small handheld devices.


Varying bit rate is likely due to signal strength variations. That's normal.

20dBi or more gain antennas are most always used on

If you are using this indoors, for in-home coverage, it should be omni-directional on the horizontal plane. An ordinary rubber-ducky rod antenna on a WiFi device is about 3dBi. Its omni pattern is like a squished sphere. Omnis are practical up to about 12dBi where the pattern is like a bagel. Tradeoff is that with the antenna on the first floor, the signal on a 2nd floor would be really weak due to the pattern.
 
I am using a setup where I have a high gain directional antenna (max 27 dBm) pointed at a open wifi which I connect to. The antenna is bought from ebay and connected to a TP-link WA730 running openWRT LuCI.

That's your problem... big gain antennas improve signal, but they improve it everywhere - not just for the AP you're trying to attach to... so you're basically fighting noise along the directional path pointed towards that AP.

Not much we can do to help you here other than perhaps to put the OEM antenna back on and live with what you have...
 
Thanks for the explanation, stevech. This is the antenna I bought (16dbi).

http://www.dx.com/p/2-4ghz-16dbi-directional-high-gain-16-unit-antenna-for-wifi-wireless-network-rp-sma-33016#.VZBvPfntmvo

Unfortunately it has a very long (150 cm) and not large diameter cable, but afaik this should not cause the sudden drops in bit rate? The problem is that during the drops in bit rate I might get high ping and slow loading on streaming, which is why I want to try to eliminate it as much as possible.

The picture I attached shows how the antenna is mounted outside on the wall. I will later today try to attach the OEM antenna and see how it works out.
 

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It won't cause sudden drops, but you are likely losing 3-4dB of signal due to a 1.5m narrow diameter cable.

As for the drops, happens. Variations in the environment, etc. Other issues you can be seeing are "variable" Fresnel effect if you have any kind of wind and anything resembling foliage in the way (as tree branches move around). Also possibility of deviations in antenna pointing from wind (granted, a few fractions of a degree isn't going to change much on a 16dB directional antenna).

Lots of factors here can change things from moment to moment, especially if this is a relatively long link (in the thousands of feet) or at least medium distance link (in the hundreds of feet).
 
The antenna link says it's a yagii, 16dBi gain.
26 degrees of horizontal beamwidth.
23 degrees of vertial beamwidth.
It's like a highly focused flashling - a spot light.
Rather critical to aim.
Need to be above obstacles - e.g. cars/trucks on roadway, tree canopy.
 
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the sudden drops are usually caused by interference since you're still using an area based antenna, not a point to point one. The interference can be numerous from many different things. sfx2000 does have a point relating to noise but it is likely that sudden drops are just interference. Even with normal wifi use there are always sudden drops that relate to interference but as long as 90% of the time it doesnt drop suddenly than it has nothing to do with your config unless its a hardware issue.
 
@system error
That antenna is a yagii, narrow-beam. It is normally used for point to point links where the narrow beamwidth is acceptable.
 
the sudden drops are usually caused by interference since you're still using an area based antenna, not a point to point one. The interference can be numerous from many different things. sfx2000 does have a point relating to noise but it is likely that sudden drops are just interference. Even with normal wifi use there are always sudden drops that relate to interference but as long as 90% of the time it doesnt drop suddenly than it has nothing to do with your config unless its a hardware issue.

If OP is using a big yagi to pull some free wifi...

1) He's probably picking up other traffic on that BSS - remember, WiFi is single frequency, so other clients on that AP are contributing to his noise floor

2) Time-Delay issues - yes, using a yagi or high-gain patch antenna can seriously extend range, but the AP is using time to manage traffic and management frames (Beacon's and other) - pulling things out from let's say 25 meters to 250 meters, this affects time management for all clients associated with the primary AP, so OP is likely impacting everyone that is trying to use that AP

3) Free is what OP gets - he's not paying for Open WiFi, so perhaps, he should be happy with what he gets.
 
If OP is using a big yagi to pull some free wifi...

1) He's probably picking up other traffic on that BSS - remember, WiFi is single frequency, so other clients on that AP are contributing to his noise floor

2) Time-Delay issues - yes, using a yagi or high-gain patch antenna can seriously extend range, but the AP is using time to manage traffic and management frames (Beacon's and other) - pulling things out from let's say 25 meters to 250 meters, this affects time management for all clients associated with the primary AP, so OP is likely impacting everyone that is trying to use that AP

3) Free is what OP gets - he's not paying for Open WiFi, so perhaps, he should be happy with what he gets.
I never take internet from open wifi because they're so slow that you cant even open a web page and lack security. I guess you get what you paid or lack of paid for.
 
Yes, I am picking up someones WiFi, but that is becuase the local ISP wont install broadband around here because of poor and old copper cables. This is because we will pay for e.g 6 Mbit and receive around 1-2 Mbit of laggy internet. Another ISP has a survey going to see if there's interest in digging a fiberoptic cable in the neighbourhood. I'm crossing my fingers for that. This just a temporary "fix" to have internet access during the summer. For security reasons I have the AP/client with the antenna connected to an Asus RT-AC66U running Merling which is the router in our house I connect to.

I do this mostly to see what is possible and to learn how to set up a network in different ways. That is also why I'm asking you guys :)

The WiFi I'm picking up has three different networks on the same channel. I will try to point the antenna in different ways to see if the bit rate becomes more consistent.
 
Well you could always set up internet in another building where it is available and than create a point to point link between that building and yours using 2 wifi APs with directional antennas/dishes. If you ask the owner of the building he may let you purchase your own internet to his building and you just route it via wifi to you. Normally i avoid free wifi because its very unreliable.
 
Yeah, we really can't help you leech off of someone else's internet. I'm guessing it violates the terms of use.
 
yes, for unusually
Yes, I am picking up someones WiFi, but that is becuase the local ISP wont install broadband around here because of poor and old copper cables. This is because we will pay for e.g 6 Mbit and receive around 1-2 Mbit of laggy internet. Another ISP has a survey going to see if there's interest in digging a fiberoptic cable in the neighbourhood. I'm crossing my fingers for that. This just a temporary "fix" to have internet access during the summer. For security reasons I have the AP/client with the antenna connected to an Asus RT-AC66U running Merling which is the router in our house I connect to.

I do this mostly to see what is possible and to learn how to set up a network in different ways. That is also why I'm asking you guys :)

The WiFi I'm picking up has three different networks on the same channel. I will try to point the antenna in different ways to see if the bit rate becomes more consistent.

You should (must) get permission from the WiFi access device's owner in order to use that service. It's the right thing to do. But most are encrypted these days, making it moot.

bad copper... Is there no cable modem option for you?
 

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