View Single Post
Old 6th Jul 2020, 10:32 pm   #19
Radio Wrangler
Moderator
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 22,799
Default Re: FM signal boosting

You don't just get signal from an aerial, you get thermal noise created by the resistance of the elements and their temperature as well as thermal noise from the world around it. The effective temperature decreases if you aim above the horizon. Space is cooler than the earth. with the notable exception of stars! It was someone noticing this on a microwave link that led to the discovery of the 3 Kelvin background radiation anf thence the big bang theory. So if you have a very low signal and you stick in even a good amplifier every dB of gain you give to the signal, you give the same to the noise.

The preamp pays its way if your tuner has a poor noise figure, because then a low noise preamp can lift the signal and although it also lifts the incoming noise, the tuner was dominant, so you can get a net gain in signal to noise ratio.

Cable loss adds to the noise figure of whatever gear follows it. So mast-head preamps with a fair amount of gain can take out this contribution. Once you lose on noise figure, you've lost it forever.

Most people avoid studying noise because no-one likes it, but it's a case of know thine enemy and you can if not win, at least lose by less.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now