[amsat-bb] Re: perfect groundtrack contest

[i8cvs]

Hi Hovie,AB2S

You are correct but there is another reason that make very difficult to
use a commercial satellites for amateur communications.

The Amateur Satellites and our ground stations are FDMA i.e Frequency
Division Multiple Access in wich the satellite passband is shared at the
same Time by all ground users depending on the frequency that they
chouses for the uplink and downlink.

On the other side the Commercial Satellites are mostly TDMA i.e. Time
Division Multiple Access in wich a master Ground Stations send to the
satellite transponder the sincronization pulses to switch the onboard
multiplexer at very high speed and specific Time between all client ground
stations as explained in the following web page.

http://www.satsig.net/vsat-equipment/tdma-explanation.htm

In simple word the TDMA often called "switcher" operate as a citizen
Telephone Central Station that is not on earth but on board of the
satellite.

73" de

i8CVS Domenico

----- Original Message -----
From: "Howie DeFelice" <howied231 at hotmail.com>
To: <w7lrd at comcast.net>
Cc: <amsat-bb at amsat.org>
Sent: Friday, June 15, 2012 11:31 PM
Subject: [amsat-bb] Re: perfect groundtrack contest
>
> Unfortunately the hardware on board isn't programmable. The shared
> antenna's are connected to very frequency specific bandpass filters that
> form the multiplexer, the frequency translators are fixed and if the HPA
> is a TWTA it is also very frequency dependent. By the time the commercial
> operators are done squeezing every last penny out of them, there isn't
> much left over to use anyway :)
>
> - Howie AB2S
>
> Date: Fri, 15 Jun 2012 21:18:46 +0000
> From: w7lrd at comcast.net
> To: howied231 at hotmail.com
> CC: amsat-bb at amsat.org; tomdoyle1948 at gmail.com
> Subject: Re: [amsat-bb] perfect groundtrack contest
>
> I have also "wondered" if any of the older commercial surplus satellites
> can be "reprogrammed"  for our use.  I realized that idea is no doubt an
> over simplification.  Today's speculation can be tomorrows reality.
> 73 Bob W7LRD
>
>
>
> From: "Howie DeFelice" <howied231 at hotmail.com>
> To: amsat-bb at amsat.org, tomdoyle1948 at gmail.com
> Sent: Thursday, June 14, 2012 12:48:06 PM
> Subject: [amsat-bb] perfect groundtrack contest
>
>
> I vote for Intelsat G-11 at 304.5 deg E. This is a Ku band only bird,
> however, the semi-retired Intelsat 805, which is co-located with this sat
> has a global C band beam with a downlink that extends into the amateur 9cm
> satellite band (3400-3410 MHz). I often wondered if Intelsat would
> consider "donating" a few Khz  to AMSAT. We could then tie a single,
> commercially licensed uplink station via echolink and hear it on the 9cm
> downlink. At least it would be a reason for people to use the 9cm band
> before it's taken away for the latest mobile broadband gizmo.
>
> Howie AB2S