How to conveniently and quickly convert the ratio of dB to power and vice versa

With the help of this table, we can very quickly find out the power ratios from 0 dB to 69 dB. We can also find power ratios from 1:1 and up to 1:8 million.

First of all, we have to pay close attention to the decimal point, but otherwise the table is very easy to use. I found this little article in CQ-DL 4/78, page 168.

A few examples for using the table

1. What power ratio does +7dB amplification correspond to?
We look for 0 dB in the upper line and 7 dB in the left column, which gives us 07 dB. The decimal point will be to the right of 07 dB, or between 0 dB and 10 dB of the top line.
The result is a numerical field to the right of +7 dB = 5.011872 times the power gain.

2. What power ratio corresponds to +13 dB gain?
We look for 10 dB in the upper line and 3 dB in the left box, which gives a total of 13 dB. The decimal point is to the right of 13 dB, or between 20 dB and 30 dB.
The result is a numerical field to the right of +13 dB = 19.95262 times the power gain.

3. What power ratio corresponds to -25 dB attenuation?
Top line 20 dB, left line 5 dB. The decimal point is between 20 and 30 dB. The result is -25 dB = 316.2278 multiple attenuation.

4. What power ratio corresponds to an attenuation of -48 dB?
Top line 40 dB, left 8 dB. Decimal point between 40 dB and 50 dB. We read in the number field -48 dB = 63,095.73 multiple attenuation. The power is damped in a ratio of 1:63095.

Calculation of dB from the power ratio

1. The power has been increased 350 times. How many dB is that?
We look for the number 350 in the table. We find only 316 and 398, our number lies between them. In the third column of the number 316 above, we find the number 20, on the left we find the number 5. So the power ratio is 20+5 = 25 dB.

2. The power was increased 20,000 times. How many dB is that?
We look for the number 20,000, the closest is 19,952, we find 40 dB in the last box and 3 dB to the left. The result is 40 + 3 = 43 db.

3. Performance was reduced by 1:13.600. How many dB is attenuation?
We look for 13,600 in the number field. The closest is 12589. Up we get 40 dB, to the left we get 1 dB, that is 40 + 1 = – 41 dB.

4. Power is damped 650,000 times. How many dB is that?
We look for the number 650,000 in the number field. The closest is 630 957, up is 50 dB, to the left is 8 dB, the result is 50 + 8 = – 58 dB.

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