> Re: time-nuts Digest, Vol 108, Issue 29 > On Fri, 05 Jul 2013 19:55:42 -0400, [email protected] wrote: > > > Message: 6 > Date: Sat, 06 Jul 2013 00:27:33 +0200 > From: Magnus Danielson <[email protected]> > To: [email protected] > Subject: Re: [time-nuts] Speaking of Costas loops > Message-ID: <[email protected]> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > On 07/05/2013 10:39 PM, Joseph Gwinn wrote: >>> Re: time-nuts Digest, Vol 108, Issue 28 >>> Message: 2 >>> Date: Fri, 05 Jul 2013 09:18:39 -0700 >>> From: Jim Lux<[email protected]> >>> To: [email protected] >>> Subject: Re: [time-nuts] Speaking of Costas loops >>> Message-ID:<[email protected]> >>> Content-Type: text/plain; charset=ISO-8859-1; format=flowed >>> >>> On 7/5/13 8:44 AM, Bob Stewart wrote: >>>> Wouldn't a Cs or Rb clock in orbit be slow due to relativistic >>>> effects? I'm pretty sure there is a relativistic correction to the >>>> GPS clocks. >>>> >>>> Bob - AE6RV >>>> >>>> >>> >>> I believe that the original WAAS repurposed transponders intended for >>> other L-band satellite signals (e.g. Sirius/XM/LightSquared). >>> >>> As noted earlier in the discussion, the new satellites might have a >>> specialized payload, which could have a purpose specific coherent >>> transponder, rather than a linear translator. >>> >>> If it is purpose specific and single channel, then making it immune to >>> the local oscillator is straightforward. >> >> I worked on a proposal for the original WAAS system. The WAAS signal >> is not a timing signal in the sense that GPS signals from space are >> timing signals. WAAS instead sends out a stream of correction data >> that allows one to greatly improve the accuracy and reliability of GPS >> signals. >> >> So, unless things have changed greatly, the geostationary satellite >> that broadcasts the WAAS signal need not have an atomic clock. > > This is naturally still true, but we are into the level of "there's a > signal here, what can we use it for?". Doing a much simplified receiver > could serve some well enough, without going the full monty. It's like > taking the color-carrier of analog TV broadcasts.
OK. Given that the birds WAAS uses were built for communications purposes, not timing purposes, I'g guess that their frequency reference is a very good quartz unit. I suppose Rubidium is possible, but Cesium is very unlikely. Bent-pipe channels do a frequency change to eliminate singing. I imagine the datasheet for the rentable comm channels will give the frequency error and stability of the downlink signal. Joe Gwinn _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
