# [amsat-bb] Re: Arecibo on 432 MHz Moon Bounce (some calculations)

i8cvs domenico.i8cvs at tin.it
Wed Apr 21 10:49:23 PDT 2010

```----- Original Message -----
From: "Fabio A" <iw8qku at amsat.org>
To: <AMSAT-BB at 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

"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

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

```