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Re: Just to be clear - eirp vs transmitter power



good tips Edward, ill need to update my web page.
Many people get confuged with db, dBd, dBi, etc.
And with power and erp.  

it may be time to update my "how much power" page
http://www.marexmg.org/fileshtml/packetpower.html


Here is tip on translating antennas.
The letters "dB" are never used for an antenna gain.
If you see the letters "dB" or "db", then that is a
value
invented by the Marketing team selling the antenna.
If you want to "ball park" the real antenna gain, then

you have two options.  Subtract "3" or count the
number
of half-wave dipoles.  Then you will be able to more
accuratly estimate the antenna performance.

Below is a simplified antenna gain chart. 
This chart assumes the antenna is made up from 1/2
wave dipoles, hence the term dB(dipole) dBd. 
It is normal for the published antenna gain numbers to
be distorted. 
When comparing antennas always just count the number
of Dipoles the antenna is made from then use the gain
chart
below. Each time you double the number of Dipoles, you
increase your gain by 3 dBd. 
If you want your radio to hear better, get a bigger
antenna. 
The bigger antenna will also make your transmitter
appear to be bigger too. 
(this chart does not take into consideration coax
loss) 

  Antenna    Gain     Transmitter      Estimated 
  Elements   dB        Power	         ERP
  1          0               50                50
  2          3               50                100
  4          6               50                200
  8          9               50                400
  16          12               50              800
  32          15               50              1600


--- "Edward R. Cole" <al7eb@acsalaska.net> wrote:

> At 11:12 PM 1/16/2006 -0800, Emily Clarke wrote:
> >I stated about 35W to get into AO-51 SSB, but that
> was about 6W at 
> >the transmitter into a 9db gain beam antenna.  My
> neighbors would 
> >kill me if I was putting out 35W at the
> transmitter.
> >
> >73,
> >
> >Emily
> >
> 
> 
> Whew!  Glad you cleared that up.  Actually we
> satellite operators should
> get used to talking about ERP when discussing up
> link requirements.  
> 
> Remember:
> ERP (watts) = power (watts) x antenna gain ratio
> (not dB) or, 
> ERP (dBm) = power (in dBm) + antenna gain (dBd) or,
> EIRP (dBm) = power (in dBm) + antenna gain (dBi)
> dBi = dBd + 2.1
> dBd is the gain over a std dipole
> dBi is called the isotropic gain (used for most
> technical papers)
> 
> If you have long coax runs you can subtract line
> loss (in dB) or convert
> loss to a ratio and use the appropriate formula
> (above).
> 
> For those who are dB challenged:
> 3 dB = a ratio of 2
> 6 dB = a ratio of 4
> 7 dB = a ratio of 5
> 9 dB = a ratio of 8
> 10 dB = a ratio of 10
> 
> so an antenna of 13 dB = a ratio of 10x2 = 20
> a cable with 6 dB loss = a ratio of 1/4 = 0.25
> 
> My UHF station: 60w, 16.5 dBd antenna:  ERP = 60 x
> 50 = 3000w (approximately).
> 
> Now I hope I did not insult anyone with this
> explanation but I know some
> hams are a bit intimidated by math.
> Hope this helps!
> 
> 73's,
> Ed - KL7UW 
> ===================================
> BP40iq,  Nikiski, AK      http://www.qsl.net/al7eb
> Amsat #3212
> Modes: V - U - L - S
> ===================================
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