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What is the difference between dB and %, and what is a good number?

posted Jun 28, 2017, 2:29 AM by Amir Borenstein, No Rad   [ updated Jul 1, 2017, 12:44 AM ]
Q - in the fabrics' RF reduction info, some sites show the reduction effect in dB unit, some in %, your site shows both.
What is the difference between dB and %, and what is a good number?

A - dB is the bumping effect of in logarithmic nature.
It is usually used in professional RF protection since the difference between -0dB and -100 dB is very big. 
The following table is a conversion between dB and %

RF Reduction dB/%
 dB %
 -40dB 99.99%
 -50dB 99.999%
 -60dB 99.9999%

Well I think that measuring in dB is highly misused when it comes to every day RF protection, specially in clothes and hats.
The use of dB units comes from the military and professional world of RF protection, where sometimes you need to go down  -90db or even lower.
In case that you have only one penetration point (happen in the military or professional world but not so much in the real world) then a protection material with -20 db will be better than one with -15db and much better than -10db. 
But in every day world, were there are many penetration points and the installation is usually not perfect, if you pay more for a  -50db (~99.999%), or even -35db(~99.97%) compered to a -25db(~99.7%) or -20db (that ~99%), I think that at-least in some cases it is a waist of money. 

For example, if you protect a car, and you don't protect the front wind shield (since in most countries it is illegal and because it can distort the road view, specially at night) then more RF will come from the front wind shield than the difference between RDF62 and RDF72, and the price for the RDF72 will be double. 

Second example, if you need curtains, and you install the curtains in a way that there are not glue to the wall or window (there is some air between them), then more RF will come in from this gap than the difference between -25dB to a -35db fabric. 

Third example, if you are looking to make a hat, more RF will come in to the head from the places you can't cover, than the difference between a -20db to a -30db fabric.

RF Protection Reduction