Never a daft question!

The PLL is an indication that the carrier is present, used for a different =
purpose, while of course the FSK has the data packets.  But I am open to ot=
her choices on data transmissions but I do need some indication that the ca=
rrier is present.

--- On Wed, 3/10/10, Peter Restall <pete@restall.net> wrote:

> From: Peter Restall <pete@restall.net>
> Subject: Re: [PIC] DSpic - PLL
> To: piclist@mit.edu
> Date: Wednesday, March 10, 2010, 8:52 AM
> =

> On Tue, 9 Mar 2010 13:23:07 -0800 (PST), alan smith wrote:
> =

> > Just curious...not having any experience in
> DSpics.=A0 Looking at detecting a
> > 38KH
> > z signal, bascially doing the function of a PLL (this
> is a sine wave coming
> > in) =

> > and also doing FSK decoding.=A0 Essentially this is
> a 38KHz subcarrer that has
> > FSK
> >=A0 (38K/42K) and presently doing it with a 16F PIC
> and an external PLL chip
> > (567 I
> >=A0 think..?).=A0 Can the DSpic do the PLL
> function..obviously it can do the FSK
> > deco
> > de.
> =

> Hello Alan,
> =

> Might be a daft question, but why a PLL ?=A0 I'm
> currently doing something
> similar, but with a 60KHz signal.=A0 I just feed the
> (amplified and anti-aliased)
> signal into an ADC pin and then run it through a Goertzel
> routine.
> =

> Olin provided details of a very nice algorithm for
> magnitude detection a while
> ago in relation to an MSF / WWVB receiver (search the
> archives), but if you're
> interested in FSK rather than ASK then the Goertzel
> algorithm is probably a
> good choice - I had Olin's algorithm working in simulations
> but haven't
> transferred to firmware yet.
> =

> The good thing about the Goertzel algorithm is that you can
> give it multiple
> frequencies for your different FSK states, and it's pretty
> lightweight in
> terms of computation (for a dsPIC, and versus a full
> FFT).=A0 You could also
> get rid of that 567 and other hardware and simplify the
> circuit somewhat.
> =

> Regards,
> =

> Pete Restall
> -- =

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