[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

R: R: 3m dish applications




----- Original Message -----
From: Anthony Monteiro <aa2tx@comcast.net>
To: Robert Bruninga <bruninga@usna.edu>; <amsat-bb@AMSAT.Org>;
<domenico.i8cvs@tin.it>
Sent: Wednesday, April 07, 2004 3:29 AM
Subject: Re: R: [amsat-bb] 3m dish applications


>
> At 08:25 AM 4/5/2004 -0400, Robert Bruninga wrote:
> >I would like to do 2.4 GHz microwave oven CW for EME.
> >Yes, I konw that the signal from an oven is very poor and
> >very broad and full of 60 Hz noise.  This  makes it not receive
> >well on a narrowband receiver.
> >
> >BUT!  Why cannot someone with a DSP soundcard, invent
> >a wideband detector for 60 Hz microwave oven.  Taking the
> >broadband  CW "signal" energy out of a broadband receiver
> >with DSP should give "processing gain" shouldnt it?
>
>
> Hi Bob,
>
> A typical oven magnetron has an output of around 800 watts
> (+59 dBm) and a bandwidth of over 2 MHz. If you put the magnetron
> right at the focus of a 10' dish (Gain = +36 dB), you would get
> an impressive +95dBm EIRP.
>
> For the receiver, lets assume a preamp with .5 dB noise figure,
> also mounted right at the focus of another 10' dish. However,
> this receiver needs to be 2 MHz (or more) wide so the resulting
> receiver sensitivity is around -153dBm.
>
> The eme path loss to the moon and back is around 280 dB so
> the resulting return signal is +95 -280 = -185dBm and
> the signal to noise ratio is -185 - (-153) = -32 dB
>
> It would be very tough to pick this signal out of the noise
> even with a really good DSP since the oven signal is so unstable
> and it is over 2 MHz wide so sound cards are out.
> You can't get the same "processing gain" that you would with
> spread-spectrum because the TX signal is not predictable.
>
> Now, compare the same setup with 10 dB less output (i.e. 80 watts)
> and a 100 Hz bandwidth. The TX EIRP is then only +85 dBm but the
> receiver sensitivity is now -196 dB giving a SNR of around 1 dB.
> Heck, you can hear that in your headphones.
>
> Or try 8 watts (+75dBm) and a simple sound card program to pick out
> the -9 dB SNR return signal and you are in business.
>
> 73,
> Tony AA2TX (Back from vacation!)
>
>
Hi Tony ,AA2TX

And if you increase your power from 80 watt to 500 watt using my
power amplifier for 23 cm as i suggested to Bob you will get your own
echo with SNR of about 8 to 9 dB off the moon with a BW of 500 Hz 
on CW with a 3 m dish.

If you increase the BW of your Rx from 500 to 2400 Hz you will
still get an echo with SNR of about 2 dB in SSB wich is barely audible
in to the noise by hear from you but is very well audible 8 dB over the
noise by someone using 6 m dish wich is an usual size for most EME 
operators.   

And if the above EME operator is using as well 500 watt at the feed
wich is a standard power for EME you made a nice SSB QSO off the 
moon because you will hear him with 8 dB over the noise as well.

Waiting for a new HEO satellite i am looking for a 3 m dish !

73" de

i8CVS Domenico
   
>
>
>
>







----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home