[opendtv] Re: "Live" DTV from Mars now possible !
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "OpenDTV (E-mail)" <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 10 Aug 2004 18:12:10 -0400
> The site goes on to make a big deal about the use of the 8 GHz band.
> Might sound high compared with AM and FM radio, which they compare
> it to, but it sounds completely average when compared with 802.11a
> or MMDS or radar.
>
> How strange to hype up the center frequency. The high frequency
> might help in terms of SNR, but it hurts in terms of propagation
> loss.
>
> They do say that there are redundant 100 watt amps for the X-band,
> which would be this comm channel. So doing a little math, at 100E6
> Km, propagation loss at 8 GHz is an amazing 270.5 dB.
>
> The 100 watt transmitter power and 270.5 dB propagation loss
> says that with unity gain amps, the receiver would see only
> -220.5 dBm.
>
> Not sure what a state of the art receiver sensitivity figure might
> be. Maybe -110 dBm? If yes, that would imply a need for 160.5 dB
> antenna gain, some provided at the transmitter, most at the
> earth-bound receiver. No wonder they're so humongous.
>
> To get the bandwidth of this channel, assuming a SNR requirement
> of 1 dB, the 6 Mb/s channel would be 5 MHz wide minimum, almost
> like a TV station. But I have no idea if 1 dB is reasonable.
Looks like 0 dB of SNR is more like what you'd expect. So make
that a nice, even 6 MHz of channel bandwidth.
Just like ATSC!
Bert
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