RT3070 wireless adapter adjust tx power??

1. You are probably right about this. Even some channels are blocked, depending upon the country settings.

2. There do exist high power devices. I have an alpha wifi stick that claims to be high power.

It will drain more than the allowed 500mA from your usb port.

Most pc's only care about the total current used on all usb ports, so on a pc this can work.

Wifi communication is bidirectional. It's useless to have a high power stick if the access point is unable to transmit in high power as well.

For some cheap adapters without external antenne, sending more power could extend the usable range a little. High power devices usually will have a good antenna as you don't want the RF radiation to interfer with the surrounding chips.

1. You are probably right about this. Even some channels are blocked, depending upon the country settings.

2. There do exist high power devices. I have an alpha wifi stick that claims to be high power.

It will drain more than the allowed 500mA from your usb port.

Most pc's only care about the total current used on all usb ports, so on a pc this can work.

Wifi communication is bidirectional. It's useless to have a high power stick if the access point is unable to transmit in high power as well.

For some cheap adapters without external antenne, sending more power could extend the usable range a little. High power devices usually will have a good antenna as you don't want the RF radiation to interfer with the surrounding chips.

NEW QUESTION:

Where can I find the db.txt file?

This will allow me to change the allowed txpowers for each country.

Hi Fergus,

The easiest why to find files is to install locate using 'sudo apt-get install locate' Once you have it installed run 'sudo updatedb' afterwards run 'locate db.txt' to get a list of every file named db.txt. You can then add updatedb as a cron job and have it automatically update the file list db and then locate we stay up to date.

Mike

Couldn't find it.  Any one know where the information about wireless power is stored?  I read about a file called db.txt but I could not find it.

Anyone know why I can't get an IP address with my RPi as an Access Point?

http://www.raspberrypi.org/phpBB3/viewtopic.php?f=36&t=31404

This topic has sort of gone dead but...

I have found a way that you can stop the Linux OS (using BT5 in a Virtual machine for a start) from limiting tx power...

What I want to know though is:

1.  Is it telling me the truth that you can put 1.1A@ 5 volts into a Kinamax TS-9900 without blowing it up?

     NOTES:

     -  It 'claims' to have a txpower of 5800mW with a 58dBi Antenna.

     Transmission Power: 5800mW @ 38dBm ± 1dBm - http://forum.lowyat.net/topic/2414082/all

2.  What are the signs that it is not copeing with the 1.1A of power?  Fire?  Smoke?  Burning Electronics Smell?  Heat?

These are very ambitious figures.

I doubt its posible to get 58dBi out of that antenna design.

I have a 32km wireless link, that has a 24dBi grid pack antenna on the roof, and the TX power is 29dBm, and we are limited to 2MBps, although it probably will do more.

With 2.4GHz, interference and close objects can cause the biggest loss of performance, despite the power settings.

Mark

Mark,

I have done tests in windows 7:

It can see a network about 2.5 km away in a dense populated area with 20 story buildings

I don't know if that can help work out the max tx power?

(only used one USB port .: 500 mA draw)

I'm pretty sure (from the numbers mentioned) the card has 20dBm power output, and the antenna is 17dBi. This would be how they derived their so-called "equivalent" of 5800mW (which is not true). It means if your antenna radiated outward equally, then yes you'd need 5800mW for the same range, but actually on a lower transmit power the antenna is directional and has a 17dBi gain for the same range but no longer in all directions.

I'm not familiar with many antenna topologies, but from a google search it does look like there is a topology that offers 17dBi.

Then why advertise it has 5800mW 58dBi ???

Why I first looked at the numbers, they don't add up.

Here's another catch though...

It claims range upto 5km.

http://www.moxa.com/newsletter/connection/2008/03/Figure_out_transmission_distance_from_wireless_device_specs.htm

Link above explains range of Wireless.

EDIT: Removed wrong answers.

I built a python script to do all the hard-work

from math import *
while True:
    txpower = input('Enter TX Power in dBm value: ')
    txgain = input('Enter TX Antenna gain in dBi vaule: ')
    rxgain = input('Enter RX Antenna gain in dBi value: ')
    rxsensitivity = 81

    if txpower >= 50:
        txpower_dBm = 10*log(txpower/1, 10)
        txpower_mW = 10**(txpower_dBm/10)
       
    elif txpower <= 50:
        txpower_mW = 10**(txpower/10)
        txpower_dBm = 10*log(txpower_mW/1, 10)

    base = 41.88*2442
    power = (txpower_dBm+txgain+rxgain+rxsensitivity)/20

    top = pow(10, power)

    answer = top/base

    print " Your Range is about: ", answer, " km!"
    print " "

Just put in anything you want to test and it will work it out.  It even converts the txpower to dBm when you put in mW

Here is a summary of new results using script above:

ANSWERs:

1. 100mW / 58dBi = 1097.10366882  km!

2. 500mW / 58dBi = 2453.19838186  km!

3. 5800mW / 58dBi = 8355.29261538  km!

4. 100mW / 17dBi = 9.7779467407  km!

5. 500mW / 17dBi = 21.8641535926  km!

100mW / 11dBi ( This is a different adapter I have) = 4.90058207752  km!

They are assuming that:

  i.  RX antenna has gain of 2dBm

  ii. RX antenna has constant -81 sesitivity

The next set of results are using some facts:

  i.  Most networks I can pickup have a rx sensitity between -53 to -79 dBm.  So lets pick a number in between: -71

  ii.  RX antenna - most corperate networks do not have 2dBm antenna gain  So I will say about 0.5 dBm for internal gain and such.

1. 100mW / 58dBi = 291.909122484  km!

2. 500mW / 58dBi = 652.728641126  km!

3. 5800mW / 58dBi = 2223.11364437  km!

4. 100mW / 17dBi = 2.60164279264  km!

5. 500mW / 17dBi = 5.8174501375  km!

100mW / 11dBi ( This is a different adapter I have) = 1.30391015413  km!

WOW!  Don't those numbers say something  

I can not pick up signals in Cairns, so that rules out the advertised 5800mW 58dBm

I can't see the 'Federal Parliment Free WiFi', so I guess that rules out 500mW 58dBm

I can't see any of the networks from  Wollongong

BUT I can see networks with-in a 2 - 4km radius from my house (which is in an undisclosed location).  So I guess that the accual tx power of this device is exactly what you said: 500mW 17dBi .

I guess one way to test what tx power is going into it will be to cut a USB cable and add a multimeter into the circuit.  I can get around to that later in the week I suppose. 

Thanks for any advice you gave along the way.  I will let you know how my testing goes in due-course.

If it is USB powered, then we know it is extremely unlikely that it really has 5800mW power output.

Given that, if you work backward, there is a 'possibility' that they are implying 'range equivalent to 5800mW but just in one direction'.

With that possibility, this means a 20dBm power output followed by a 17dBi antenna. 17dBi antennas do exist (not that I'm any expert in

antenna technology) for WiFi from a google search, so this seemed to add slightly more weight to the possibility. I seem to remember

while back you already confirmed that the device was set to 20dBm in software.

I could be (very likely) totally wrong, but I imagine you'd need to contact the manufacturer to be really sure.

The fact that they state the digits '58' in both 5800mW and 58dBi sounds like a typo - maybe they meant 38dBi (which is still not the

right way to state things but maybe they were implying a 18dBi antenna which is possibly a rounding up of 17dBi. I'm just playing

with their numbers, which is all anyone can do without further knowledge. It's all speculation, so really you'd need to check with

the manufacturer. Any of their figures could be a typo, leading any conclusion anyone makes to be wrong.

Regarding distance, anything could throw off the real world distances (antenna construction, loss in coax and connector, reflections.