[Elecraft] Question about K2's T7 windings

[G3VVT at aol.com]

3dB gain reference to what?
 
Without a reference decibel values are meaningless. With voltage, 3db gain  
is a value greater by one half and is only applicable if the impedances  remain 
the same across the item of equipment you are measuring. When  referred to 
power, 3dB gain is greater by x 2 (double). Most  of the measurements carried 
out professionally in telecoms are  related to power and do have a specific 
reference such as dBm (reference to  1mW), etc. which makes life a whole lot 
easier. Traditionally in the Cable  TV industry the decibel is related to the 
voltage at 75 ohms.
 
Bob, G3VVT