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I have a outdoor WiFi connection, each module has a 5dBi antenna, today I extended with a 16dBi directional external antenna. before it was -65dBm the received signal level now it's -83dBm, I'm a bit confused I waited to increase the value, like -30dBm? Is it a better value? enter image description here

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    \$\begingroup\$ -83 dBm is much worse then -65dBm, is this the root of your question? If so we can edit and improve this a bit more for you. \$\endgroup\$ – Kortuk Jul 24 '12 at 10:33
  • \$\begingroup\$ Yes that is my question, but this is the received signal level \$\endgroup\$ – Kicsi Mano Jul 24 '12 at 10:43
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    \$\begingroup\$ Directional antenna produce gain in one (or more) directions at the expense of reduced signal in other directions. Is your receiver on axis of the new antenna? \$\endgroup\$ – Martin Jul 24 '12 at 11:46
  • \$\begingroup\$ The problem was the fine tuning, the antenna has only 9 degree H and V \$\endgroup\$ – Kicsi Mano Jul 24 '12 at 13:53
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No. -83 in fact, is a borderline. For example, in wpa_supplicant software -90 is the threshold on which wifi client will start aggressive scanning at the expense of power consumption. -95 in reality is the level when no traffic will happen.

If you are measuring from the place where your new directional antenna is pointing to, then something is wrong.

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Now that you have a high gain antenna, you need to learn how to steer it. The Antenna, like a flashlight uses a narrower focal angle with a smaller beam to increase the intensity.

Use the dBi level to aim your antenna and keep in mind if it is a long distance with many paths from the same source, reflections can cause bright spots and cancelled waves of opposite phase with same amplitude, so those targets shift with the slightest movement < 1mm of the antenna.

Sweep your target to find how position near trees, buildings, plaster walls with hidden mesh all affect the dBi reading and aim for numbers in the -70's with -60's even better. Anything more does not help.

Theory. The input power is Pin = Ea2 A / h Z0 where Ea is the average electric field over the area A of the aperture, Z0 is the impedance of free space, and h is the net antenna efficiency.

reference book e.g. http://wireless.ictp.it/handbook/C4.pdf

If you could see by the plot of intensity with direction, it would be easier to aim. Try to keep a DIRECT LINE OF SITE for microwave signals, even though they can pass through glass and some building material, reflections ( Ralleigh fading) are a major issue to avoid.

Scan slowly and find a program to give you better feedback on SNR or signal level and try not to move.

Page 67 in link shows beam patterns and null zones that are common.

This is what likely happened to you. You were aiming near the null zone.

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