Cable gain

Discussion in 'General Electronics Discussion' started by samurai14, Apr 3, 2010.

1. samurai14

1
0
Apr 3, 2010
Hi, I have a question, what is the formula to work out the output W of a cable with 2W input and a 13dB gain......please please help....

2. (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,497
2,839
Jan 21, 2010
A cable with gain?

3. davennModerator

13,866
1,958
Sep 5, 2009
hahaha

dang thats what we all need huh steve

we could do away with expensive amplifiers then

samurai14

cables DO NOT, NEVER EVER have gain, they only have losses and the longer
the length and/or the higher the frequency used the greater the losses are

The loss is usually expressed in dB / metre or if you are in the USA dB / foot
or some variation of eg at 1000MHz (1GHz) a given cable mite have a loss of
12dB / 30 metres (100ft) a much better quality cable may only have a loss of
8dB / 30m at 1GHz

you have told us you are putting 2W into one end of the cable, we need to know at what frequency ??
and we need to know what cable type and its length ?? so we can look
up its specifications and find its losses at that freq and length.
Lets for example sake say it has 3dB loss for 10metres at your frequency of 400MHz
then you will have only 1W at the far end of the cable... 3dB loss represents 1/2 the
power lost

Now I have assumed you have been talking about an RF signal into say a coaxial cable
(thats what I mainly deal with)
but it doesnt really matter even if it is an audio signal into a long twin wire (figure 8) speaker
lead. there will still be losses, just a lot smaller

cheers
Dave
VK2TDN

Last edited: Apr 4, 2010
4. neon

1,325
0
Oct 21, 2006
cables do not have any gains ever only losses. importance is the cable lenght for cable frequency transmission . any cable must be cut at the right lenght for the right frequency otherwise it can show as virtual short.

5. Resqueline

2,848
2
Jul 31, 2009
As usual neon tells only half the story.. He's right only if the cable end is left open (or shorted). If it's properly terminated then length doesn't matter.
If the cable is not terminated with the proper impedance then the cable input impedance will vary with frequency.

But we are still in the dark here as to what the o/p actually had in mind..