At 07:22 AM 12/23/2005, Stone, Gary R. wrote:
>Hi to all,
>
>
>
>First, I hope you all have a wonderful Holiday and Merry Christmas. Thanks
>for the help on this reflector this past year.
>
>
>
>I am now trying to sort out in my head a simple way to get a rough idea
>about some gain calculations on a Yagi antenna.
>
>For example, if a Yagi has a gain of x db or x dbi (whichever) and is
>running a certain power then at what power level would you need with a
>vertical or dipole to roughly equal the Yagi? Is there a simple way to get
>a ROUGH idea and not a scientific solution?
dBi is dB relative to an isotropic antenna (one that radiates in all
directions equally, a fiction that cannot be achieved in real life, but a
convenient standard).
So, if you have an antenna with a gain of x dBi in a particular direction,
the power at the receiver will be x dB greater than they would get with an
isotrope. That is, 10^(dB/10).. Example: To a receiver, it would look the
same if the transmitter were a 100 Watts into a 6dBi antenna (pointed to
the receiver) OR a 400 Watt transmitter into an isotropic antenna.
Dipoles have a gain of 2.15dBi (theoretical... just call it 2 and be done
with it), so that same 6 dBi antenna would be 4dB better than a dipole. 4
dB is factor of 2.5, so 100W into the 6dBi antenna is like 250W into the
dipole.
Gain helps in the amateur world because we're power limited. So, someone
with a 12 dBi antenna can radiate a signal 10 times stronger than someone
with a dipole, if both of them are running the full 1.5kW. Or, the guy
with the gain antenna can run just 150W into his 12dBi antenna and have the
same signal as the guy with the dipole running legal limit. You can spend
your money on antenna gain or amplifier power, and from the transmit
standpoint, it doesn't make much difference (until you hit max legal power).
>
>
>Thanks, Gary, N5PHT
>
>
>
>
>
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
>Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
>any questions and ask for Sherman, W2FLA.
>
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_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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