Jul 222009

A receive-amplifier can have some advantage if used with a highly directional antenna.  This is because the directional antenna will eliminate  (or at least reduce) other strong signals that might be nearby, which might overload the receiver.  With a non-directional antenna, the amplifier will be amplifying unwanted signals to detrimental levels — levels that desensitize the receiver or step on  (override) useful packets.

  • Analog amplification introduces a lot of noise and thus deteriorates the overall connection
  • Analog amplifier used with an omni-directional antenna:  One savvy customer verified that it merely deteriorates their ability to establish stable connections. Other people report similar results:
  • “To be frank, I have almost never seen an amp help when added to a client device. The only time I feel one is appropriate is when it is installed at the top of a long coax run in order to overcome cable loss.”    Source:  http://www.panbo.com/archives/2008/09/5mileWIFI_first_impressions_a_conundrum.html#more

Counterpoints to the above arguments:

Distortion and noise can cancel out the advantage of amplification.  However, if the amplifier is a quality amplifier, the affects of distortion and noise will be minimized.  Problem is, the specs on low-cost amplifiers are often missing or lies.  A person just has to try it.

That said, the Alfa WiFi USB adapters already have a pretty good receiver.  Adding 15db more receive-gain might not do as well as hoped because it might be mostly amplifying noise, although I think a little more gain could help.

In our experience, an amplifier can be a noticeable benefit on the the average wireless router (if used with a directional antenna).  Years ago, we used 800mw amps to cover a small town with great success.

We believe it is best to start with a good antenna, before you try using an amplifier.

We’ve had many experiences in which a customer tries to use a WiFi booster on a USB WiFi adapter and damaged or “fried” the booster (and also situations in which the USB adapter was also fried).

What you would have to do to make the two devices work together without damaging one or the other, is to turn down the output power from the USB WiFi adapter to a level that is in the middle of whatever the power amplifier can accept.

Our customer Reed White, and RF engineer, provided all of the following commentary and info (March 2013):
If the power is turned down to the proper level (a number that is equivalent to about 15dbm output), can you say why anything would be damaged? I am well experienced with RF, and would like to understand why damage would be done if proper adjustments are made. Amplifiers are pretty common these days, and of course they would not feed their output power to the AWUS036H (instead to the antenna), although some receive gain is usually added. I guess you must have some experience with this.

Using signal-booster with an omni-directional antenna:  Most experts agree that this is a lousy option. In technical terms, it results in poor signal to noise ratio. In laymen’s terms it sounds as if someone stands next to you with a loudhailer and is tries to talk to you. You hear a lot of noise, but it becomes difficult to discern a message (due to the pain of the loud noise and spurious extra sounds that have been amplified).

With a power amplifier and with an omnidirectional (non-directional) antenna, a powerful transmitter can disturb a large area of other people’s systems.  By disturb, I mean slow down or render erratic.  This may not be an inconvenience to the guy with the high power transmitter, but it is inconsiderate of everyone else.  Therefore, it is generally considered best practice to use a very directional antenna for point-to-point connections — ideally directional antennas at both ends, with no more power than really needed.

I would say that the 1000mw of the AWUS036H is powerful enough that it should have a directional antenna in an urban environment where there may be tens to hundreds of other people sharing the same frequency.

One catch is that the 2.4GHz signals do get reflected, especially in urban areas where there are many buildings.  A person can easily get fooled into pointing a directional antenna at a reflection.  The powerful signal is then blasted where it can disturb others.  It is usually best to point the antenna directly at the other station, when possible — unless a dense building is in the way.

Amateur radio operators and RF engineers know that a good, well-positioned antenna is usually the most cost-effective way to improve range and reliability.

[end of Reed White's commentary]

General description of use of signal amplifier or booster:  Inserting an analog booster in between the transceiver and the antenna, the RF signal can be amplified.

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