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Re: R: 3m dish applications



So why is the oven magnetron so broad ?

 Is the issue primarily one of  poor power supply filtering or is it 
primarily due to a low Q resonance?

 Could  some of  "noise" bandwidth be reduced with an fm or even, a  
phase lock system, modulating an otherwise clean power supply?
     

Anthony Monteiro wrote:

>
>
>
> 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!)
>
>
>
>
>
>  
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>

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