Gain of the antenna, band conditions etc have nothing to do with db gain or
loss when turning an amplifier on or off.
Db is an expression of differences in power levels. It takes 2x the power to
have a 3 db increase. Every time you double the power you add 3 db. Going
from 100 watts to 200 watts gives 3 db. From 200 watts to 400 watts is
another 3 db for a total of 6 db up from 100 watts. If you go to 800 watts
from 400 watts (doubling again) you add another 3 db. Now you are up 9 db at
the 800 watt level from the 100 watt level.
If you replace an antenna that originally had 3 db of gain over a dipole
with one that has 6 db of gain over a dipole you add an additional 3 db of
gain to your signal.
What the guy at the other end hears in signal strength difference is the
number of db that you increased your signal strength. To make your signal 3
db stronger you can double your power or you can change your antenna to one
that has 3db more gain than the old one had. The signal strength increase
comes out the same at the other end.
You can do all of the above, increase power, and add antenna gain. They all
add together. Db is a convenient way of keeping track of power levels.
As to S units, others have noted that the old "Collins standard" was 6 db
per S unit. On most receivers the only way to really know is with an
external step attenuator that is calibrated in db.
73
Gary K4FMX
> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of WA6RKN
> Sent: Thursday, March 05, 2009 11:39 AM
> To: Tower Talk
> Subject: Re: [TowerTalk] dx blaster antenna
>
> Hi Tony...
>
> Can't speak to your figures, but.....I was always taught that 500 watts
> from
> my amplifier, not addressing any gain factors in my antenna, will result
> in
> a 3 db gain on the other end of the contact. True? I couldn't tell you,
> just what I have been told.
>
> But......
>
> On average, again, band conditions not withstanding, if I am talking to
> someone and he is cranking 80 - 90 watts barefoot, and he turns on his
> amplifier and pumps 500 watts at me, generally speaking, his signal will
> rise around 5 s-units.
>
> Again, these figures are all 'just figures'...as there are too many
> factors
> involved that will affect signal strength, etc. (Gain of the antenna is
> a
> very important factor......)
>
> Me thinks this is gonna be a good topic...I look forward to all the
> responses....I may even gather them together and post them on our New Hams
> Net Forum here in Reno. (With Talkian permissions, of course)
>
> Joe Wolfe
> WA6RKN
>
> ----- Original Message -----
> From: "k2vi" <k2vi@cox.net>
> Subject: [TowerTalk] dx blaster antenna
>
>
> > Theese are the same gullable people who get swayed quite easily to vote
> > for politicians who promise the world...That is until they get elected.
> > Anyway Im curious as to db gain vs s-unit. As I understant one S unit =
> > aproximately 6 db however on my local repeater one gentleman is adimant
> > that it's 3 db = 1 sunit. Im 95% sure it is 6=1s unit but when in slight
> > doubt I confer with the wizards on tower talk. :--}
>
> _______________________________________________
>
>
>
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