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Re: Just to be clear - eirp vs transmitter power

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.

Whew!  Glad you cleared that up.  Actually we satellite operators should
get used to talking about ERP when discussing up link requirements.  

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!

Ed - KL7UW 
BP40iq,  Nikiski, AK      http://www.qsl.net/al7eb
Amsat #3212
Modes: V - U - L - S
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