[time-nuts] Speaking of Costas loops

[Bob Camp]

Hi

The power at transmit is partially a function of making it tough for backyard "what ever nuts" to broadcast through the sats. Since there's no demodulation / decoding / encoding / remodulation, power is the only practical lockout mechanism. 

It's secondarily a function of the massive amount of random RF we generate all over the planet. They want signals that are "clean" to -60 dbc or better. They actually sell slots that are in the > -50 dbc range to people for specialized use. There is some modulation magic involved, so that's not quite the same as main transmit is 60 db >  sum of (everything else). 

http://en.wikipedia.org/wiki/Transponder_(satellite_communications)

Bob

On Jul 3, 2013, at 3:42 PM, Azelio Boriani <azelio.boriani at screen.it> wrote:

> Sure about the "bent pipe"? If so it seems that much power is required
> at the transmitting ground station...
> 
> On Wed, Jul 3, 2013 at 7:48 PM, Attila Kinali <attila at kinali.ch> wrote:
>> On Wed, 3 Jul 2013 08:29:02 -0400
>> Bob Camp <lists at rtty.us> wrote:
>> 
>>> There are two batches of GPS / WAAS sats up there:
>>> 
>>> 1) The ones with numbers above 100 that are geosync and that only do WAAS
>>> 
>>> 2) The ones with numbers <= 32 that do nav. These are not geosync.
>>> 
>>> I believe the only ones with corrected / high stab clocks on board are
>>> those in the second group. The stuff in the first group aren't dedicated
>>> sats, just leased transponders on conventional multipurpose geosync birds.
>> 
>> I don't know about WAAS, but AFAIK the EGNOS signals are generated on
>> ground using Cs references and retransmitted by the satelites using
>> a "bend pipe". Ie. the signals should be of time-nut quality even without
>> high accuracy frequency standards in the birds themselves.
>> 
>> (Sorry, i'm not able to find where i read about that, so no references today)
>> 
>>                        Attila Kinali
>> 
>> --
>> The people on 4chan are like brilliant psychologists
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