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Re: Re: [ATNA] More thoughts about HAM TV from space



>>> "John B. Stephensen" <kd6ozh@comcast.net> 12/30/05 8:37 PM
> FM ATV uses a... 20 MHz wide [signal].  The minimum 
>required signal... is... -93 dBm.  At 350 km away 
>the path loss is 153 dB at 2400 MHz. A 2 foot dish 
>has 20 dBi gain so a minimum of 10 W EIRP is required.

But we also have to add that the path is 2000 km to
the horizon, 1500 km when ISS is at 5 deg and 1200
km when it is above 10 deg.  So we should probably
plan for the 1500 km range which takes another 12 dB.
Or would need a tracking 8' dish.  Bummer.

What about VSB AM?  This would have 2 advantages.
1) ENable the use of simple readilly available MDS
down converters infront of any TV set.
2) Reduces the bandwidth from 20 MHz to 6 which
should get back about 5 dB.

If we did not use the sound sub-carrier could we do
it in 5 MHz?  We could use a 10W 2m FM downlink
for the audio.

>However, there are at least 3 standards for analog 
>color TV so only a fraction of hams will be able to 
>receive the signal.

But we would use it as a bent-pipe transponder, so 
what comes down is what goes up.  In each country, 
what they see is what they transmit.

Bob
----- Original Message -----
From: "Robert Bruninga" <bruninga@usna.edu>
To: <amsat-bb@AMSAT.Org>
Sent: Friday, December 30, 2005 21:33 UTC
Subject: [amsat-bb] Re: [ATNA] More thoughts about HAM TV from space


> OOPS... Big change in the original ATV satellite premise:
>
> The opportunity I am working on is on the ISS, so
> we cannot TX on 70 cm since that will probably be
> the main uplink band for all the other ham stuff
> on board.  SO I guess that means it will need to
> be 2.4 GHz downlink.
>
> THus, all it takes to receive it is a standard MDS
> downconverter which plugs directly into a TV
> set.  OK, lets study that approach.  Do the link
> calculations and lets see how much TX power
> (to an omni) is needed for receiving on a 2' dish.
>
> de Wb4APR, Bob
>
> >>> mvonlanthen@vtx.ch 12/30/05 12:13 PM >>>
> > 1 - The satellite rules were changed to allow HAM TV downlinks between
> > 420 and 440 MHz.
> > 2 - We could decide which of the five HAM TV standard channels to
> > use:  421.25, 426.25, 427.25, 434.00, 439.25.
>
> hb9afo---------
>
> After short study, it's not permitted to use the 1200 MHz band in the
> sens space-earth as i was proposing in my precedent message. The best
> solution would be to use DATV on 430 MHz but only between 435 et 438
> MHz, the sole permitted space segment in Europe.
>
> So use the 434 MHz channel pushed to 436,5 MHz per example for the
> downlink space to earth and 1200 MHz for uplink earth to space. But use
> DATV instead of normal ATV, it would be much easier.
>
> 73
> michel hb9afo
>
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