WiFi Tx power question

[Doug]

On 09/19/2014 07:00 PM, jd1008 wrote:
> 
> On 09/19/2014 04:50 PM, Rick Stevens wrote:
>> On 09/19/2014 02:53 PM, jd1008 issued this missive:
>>>
>>> On 09/19/2014 01:14 PM, Heinz Diehl wrote:
>>>> On 19.09.2014, jd1008 wrote:
>>>>
>>>>>            Bit Rate=72.2 Mb/s Tx-Power=15 dBm
>>>>> So, reason I am asking is that I would like to increase Tx power to
>>>>> 30dBm
>>>>> due to poor connectivity with the hotspot router.
>>>> There are two barriers:
>>>>
>>>> 1. the capability of your adapter
>>>> 2. CRDA
>>>>
>>>> For most countries, 2.4 GHz is limited to 15 dBm, so iwconfig won't
>>>> help. The only thing you can do is to check if your router has WMM
>>>> enabled for the 2.4 GHz band. If so, you have a chance that your
>>>> adapter can use HT/VHT (aka 802.11n/ac), which in turn allows a
>>>> slightly higher tx power (but quite sure not 30 dBm).
>>>>
>>>> Btw: increased tx power also leads to increased noise. You should
>>>> consider other ways to improve the connectivity to your AP (miving it
>>>> closer, using a repeater...)
>>>>
>>>>
>>> Thank you Heinz.
>>> I am also looking for a card that has much higher Rx sensitivity
>>> (i.e. can receive lower strength signals without problems).
>>
>> Try to find a USB adapter with an external antenna. This is one and I
>> believe it works with Linux:
>>
>>     http://www.newegg.com/Product/Product.aspx?Item=N82E16833704045
> 
> Well, what about this one with long range capability (whatever that means :) :)
> 
> http://www.ebay.com/itm/TP-LINK-TL-WN822N-Wireless-N300-High-Gain-USB-Adapter-WIFI-Adapter-Long-range-/261441336867?pt=US_USB_Wi_Fi_Adapters_Dongles&hash=item3cdf1e3623
> 

First: Higher power does NOT increase noise in the signal. It just increases the amount of 
radio frequency energy in the general area, which may be "noise" to some _other_ piece of equipment.

A previous post recommended  http://www.newegg.com/Product/Product.aspx?Item=N82E16833704045.
The antenna in the previous post has a _detachable_ external antenna. surely that antenna will 
have a "reverse polarity" connector, but there are adapters for those things. There are two 
advantages for a detachable antenna with a connector on it:
1. You can connect a cable between the adapter and the antenna, and put the antenna is a 
more favorable location, and,
2. After you connect the cable to the adapter, you can look for an antenna with a higher gain.
That will probably make the effective radiated power exceed legal limits, but it _will_ provide
greater range.

The antenna recommended in this post (above) is actually two antennas, both apparently connected
to the dongle without connectors, but that's not certain. The advantage of two antennas, is what is 
called "diversity."  The reason that diversity is advantageous is that in any environment 
with reflecting surfaces--like the room where your computer is located--
the reflections of the RF signal will cause spots with higher field strength and spots with lower.
The use of two antennas is intended to put at least one of them in a spot with higher signal strength.
(This frequently works, but not always.)

I hope this discussion has made some of the possibilities more clear.

--Doug, retired RF engineer.