[time-nuts] Speaking of Costas loops

J. Forster jfor at quikus.com
Tue Jul 2 14:44:22 EDT 2013


There is a Wiki article on Costas Loops that includes block diagrams.
There are books about the loop filter design.

Signal squaring is simply the Trig identity:

Sin(A)**2 = 1/2*[1 - cos(2*A)]

which has a DC term and a double frequency term. Sine is symmetriv about
the 0 axis.

In practice, with low S/N the Costas Loop is probably better.

-John

==================


> Here we go again - the first send didn't seem to get through. This is
> the second attempt.
>
> This talk of Costas loops reminded me of something I wanted to
> investigate some day. I read somewhere a while back about
> carrier-phase measurements, and various methods for recovering the
> GPS carrier frequencies, including the Costas loop, and something
> with carrier-squaring. Nothing I found showed actual examples or
> detail of how this is done, only high-order mathematical descriptions.
>
> For my needs, I'm more of a frequency-nut - I usually don't care
> about getting time info, but I'd like perfect 10 MHz for reference.
> Can using only the carriers lead to simple ways to get the same (or
> better) frequency stability as a conventional GPSDO, but without the
> time and location info, or is it pointless to worry about it, and
> just go with full GPS decoding of everything? Or, is carrier-phase
> just an enhancement only if you already have the full GPS info?
>
> I know that the group could redesign the whole GPS system with tubes
> if necessary, considering recent philosophical discussions on that,
> so I think there's plenty of knowledge here about carrier-phase
> related stuff too.
>
> Ed
>
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