[TowerTalk] Coax Loss

[Jim Brown]

On Thu, 4 Feb 2010 10:38:27 -0600, Jim Miller KG0KP wrote:

>I have struggled with this and have seen it both ways.  

>Take an example of 100 feet of some coax at 5 db loss.
>Is the loss at 200 feet 8 db or is it 10 db ????
>And is the loss at 50 feet 2 db or 2.5 db ????

At 200 ft it's 10 dB and 2.5 dB at 50 ft.  Loss is dB per 
unit length of cable. So if you double the length, you 
double the loss. 

The "rules of thumb" for 3 dB is that double (or half) the 
power is 3 dB, double or half the voltage is 6 dB. Another 
convenient one is that 10 dB is 10x or 1/10th the power, and 
20 dB is 1/10th or 10X the voltage. 

So if you put 100W into that 200 ft length of cable that had 
10 dB loss, you only have 10W at the other end. 

73,

Jim K9YC