# 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.
>
>73,
>
>Emily
>

Whew!  Glad you cleared that up.  Actually we satellite operators should

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
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