Conversion Table dBm to W/m² e.g. usage of Powermeter

Unit conversion and RF calculations

Conversion Table dBm to W/m² e.g. usage of Powermeter

Postby Moderator » Friday 10. September 2010, 19:40

Assuming the use of an “idealized“ measurement setup, like our HyperLOG antenna with 5dBi gain and one of our 1m RG316U cables with 1dB damping, the following conversion table can be applied to the signal sources below (figures in W/m²):
Code: Select all
dBm  GSM900             Lambda X           GSM1800              UMTS             WLAN
+30  45                 134                180                  220              330
+20  4,5                13,4               18,0                 22,0             33,0
+10  0,45               1,34               1,8                  2,2              3,3
+9   0,36               1,06               1,4                  1,8              2,7
+8   0,28               0,84               1,1                  1,4              2,1
+7   0,23               0,67               0,9                  1,1              1,7
+6   0,18               0,53               0,72                 0,89             1,3
+5   0,14               0,42               0,57                 0,70             1,06
+4   0,11               0,34               0,45                 0,56             0,84
+3   0,09               0,27               0,36                 0,44             0,67
+2   0,07               0,21               0,29                 0,35             0,53
+1   0,06               0,17               0,23                 0,28             0,42
0    0,045              0,13               0,18                 0,22             0,33
-10  0,004.5            0,013              0,018                0,022            0,033
-20  0,000.45           0,001.3            0,001.8              0,002.2          0,003.3
-30  0,000.045          0,000.13           0,000.18             0,000.22         0,000.33
-40  0,000.004.5        0,000.013          0,000.018            0,000.022        0,000.033
-50  0,000.000.45       0,000.001.3        0,000.001.8          0,000.002.2      0,000.003.3
-60  0,000.000.045      0,000.000.13       0,000.000.18         0,000.000.22     0,000.000.33

We assumed the following center frequencies (f) here:
GSM900 (f = 900MHz), Lambda X (f = 1550MHz), GSM1800/DECT (f = 1800MHz), UMTS (f = 2000MHz) and WLAN / microwave ovens (f = 2450MHz).

0dBm is the maximum range for the HF-6060 V4 and HF-6080 V4
+20dBm is the maximum range for the HF-60100 V4
+30dBm is the maximum range for the HF-60100 V4 with our 20dB external attenuator

The conversion tables demonstrates that per 10dB step, power density decreases by a factor of 10. This applies in a similar manner to the 1dB steps, which also change in a constant manner.
Consequently, this table permits easy and fast conversion of indicated dBm values (for example, from the optional PEAK power detector, option 20x) into PEAK field strength or, respectively, power density in W/m².
This table can just as well be used with different antennas, attenuators or cables:
For example, should you be using our 20dB attenuator (option), you would extract those rows from the table whose dBm values are 20dB higher, for example, -10dBm instead of -30dBm.
As a different example, should you be using an antenna with 24dBi gain, you would use those values 19dB lower than the actual reading (24dBi minus 5dBi [as 5dBi gain is already included in the calculated table values]). For example, -43dBm instead of -24dBm.
If you were using a cable with 5dB damping, you would need to refer to those values 4dB higher than the measured value (5dB minus 1dB [as 1dB damping is already included in the calculated table values]). That is -24dBm in place of -28dBm.

HINT:
Even in case you do NOT know the frequency of the signal source, you can still achieve a comparatively exact field strength measurement by simply using the “Lambda X“ column.
This column presents a weighted average of ALL possible frequencies between 900MHz and 2.4GHz, still giving you an accuracy of approximately +/-4dB. That is still significantly better than the inherent inaccuracy of various rudimentary instruments for field strength measurement available from third parties. The frequency range from 900MHz to 2.4GHz spans a large variety of typically interesting signal sources - for example, ALL cellular phone networks (GSM900, GSM1800, UMTS) and the respective phones, as well as 2.4GHz WLAN and microwave ovens.
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