cancel
Showing results for
Did you mean:
Announcements

Welcome to Cisco Support Community. We would love to have your feedback.

For an introduction to the new site, click here. If you'd prefer to explore, try our test area to get started. And see here for current known issues.

New Member

## signal strength power and dbm

Hi,

I have a question about the signal strength power receive by a device.

For exemple, an AP is configured to send the signal with a strengh of 50mw (17dbm). One device receives this signal at -50dbm (0.00001mw).

I would like to understand if it means that the device receive the signal at 0.00001mw or receive a signal 100000 times less powerful than the original signal (50mw). In this case it means the device receive the signal at 0.005mw.

Please could you help me to understand.

Regards,

Thibault

1 ACCEPTED SOLUTION

Accepted Solutions
VIP Purple

## signal strength power and dbm

dBm scale is not a linear (it is logrithmic), so if you reduce the power level to half, dBm value won't go down by half.

Power (in dB) = 10 * log10 [signal/reference], if reference is 1mW, then it is in dBm

Using the above you can determine, power level increase/decrease by factor of 2 will become +/- 3dB. Also power level increase/decrease by 10 fold, will become +/- 10dB. Silimlary 100 times become +/- 20 dB & so on.

Therefore 50mW=17dBm, 25mw=14dBm, 12.5mW = 11dBm,...1 mW= 1dBm, 0.5mW= -3dBm....0.00001mW = -50dBm

In your case, receive signal is (50/0.00001) 5,000,000 times less powerful mean 67dB difference to the original signal,  (which is equivlant to -50dBm)

HTH

Rasika

**** Pls rate all useful responses ****

2 REPLIES
VIP Purple

## signal strength power and dbm

dBm scale is not a linear (it is logrithmic), so if you reduce the power level to half, dBm value won't go down by half.

Power (in dB) = 10 * log10 [signal/reference], if reference is 1mW, then it is in dBm

Using the above you can determine, power level increase/decrease by factor of 2 will become +/- 3dB. Also power level increase/decrease by 10 fold, will become +/- 10dB. Silimlary 100 times become +/- 20 dB & so on.

Therefore 50mW=17dBm, 25mw=14dBm, 12.5mW = 11dBm,...1 mW= 1dBm, 0.5mW= -3dBm....0.00001mW = -50dBm

In your case, receive signal is (50/0.00001) 5,000,000 times less powerful mean 67dB difference to the original signal,  (which is equivlant to -50dBm)

HTH

Rasika

**** Pls rate all useful responses ****

New Member