----- Original Message ----- From: "Fabio A" iw8qku@amsat.org To: AMSAT-BB@amsat.org Sent: Tuesday, April 20, 2010 8:26 PM Subject: [amsat-bb] Re: Arecibo on 432 MHz Moon Bounce (some calculations)
Hello all, just a curiosity, how did you found that the ERP is "... 243,902,443 Million Watts".
Thanks
73s Fabio iw8qku
Hi Fabio, IW8QKU
The only official data given for Arecibo by WF1F are the following :
The 1,000 foot dish has 60 dBi on 432 mc and 400 watts. That comes out to be approximately 243,902,443 Million Watts ERP.
enjoy
wf1f
To answere your question:
"how did WF1F found that the ERP is "... 243,902,443 Million Watts".
THERE ARE TWO POSSIBLE OUTCOMES:
Outcome Nr 1 or first possibility:
Since the given ERP is 243,902,443 Million Watts (see the WF1F above statement ) and since 60 dB is equivalent to 1000000 (one Million) time in power it comes out that the power reaching the feed of the dish must be:
243902443 / 1000000 = 243 watt
The rest of the power 400-243 = 157 watt must be losted in the feed line because the 400 watt amplifier is non mounted inside the feet but there should be a feed line long half the diameter of the dish from the feed and the operating point made of low loss big coax cable almost 150 or 200 meters long wich attenuation is 10 log (400/ 243) = 2.16 dB 10
Outcome Nr 2 or second possibility:
The 243,902,443 Million Watt ERP has been calculated in a wrong way considering the gain of the dish not 60 dBi or 60 dB over the isotropic antenna but 60 -2.14 = 57.86 dB wich is the gain over the dipole or 57.86 dBd and infact the wrong calculation showes: 10^ 5.786 = 610942 Million time in power and 400 watt x 610942 = 244,376,810 Million Watt ERP wich match very close with the value " 243,902,443 Million Watt" given by WF1F but it is a wrong value because it has been calculated with a gain of 57.86 dB instead of 60 dB
In order to know the real numbars a more informative clearification from the Arecibo Observatory Amateur Radio Club is welcome and necessary.
I hope this helps
73" de
i8CVS Domenico