Forums

Goertzel and FSK

Started by Fender123 February 14, 2012
On 2/15/2012 12:39 PM, Tim Wescott wrote:

   ...

> I'm not sure what the rational was behind the tone spacing, and I've > always been curious to know if the modem was designed to be phase- > continuous or not (if it were, then in theory it would be trellis > modulation and you could make a more-optimal decode than just a cruddy > pair of filters).
The spacing and carrier frequency together avoided problems with common harmonics. My semi-digital modem was phase coherent. Detection was the difference between the rectified outputs of two analog filters, a sort of discriminator. ... Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
On Wed, 15 Feb 2012 14:00:47 -0500, Jerry Avins wrote:

> On 2/15/2012 12:39 PM, Tim Wescott wrote: > > ... > >> I'm not sure what the rational was behind the tone spacing, and I've >> always been curious to know if the modem was designed to be phase- >> continuous or not (if it were, then in theory it would be trellis >> modulation and you could make a more-optimal decode than just a cruddy >> pair of filters). > > The spacing and carrier frequency together avoided problems with common > harmonics. My semi-digital modem was phase coherent. Detection was the > difference between the rectified outputs of two analog filters, a sort > of discriminator.
The two-rectified-filters method is (or was, at least) pretty common, AFAIK. -- My liberal friends think I'm a conservative kook. My conservative friends think I'm a liberal kook. Why am I not happy that they have found common ground? Tim Wescott, Communications, Control, Circuits & Software http://www.wescottdesign.com
May I ask one further clarification: what is different in the end result
using overlapped Goertzel, and sliding DFT? I mean apart from computational
resources. Aren't both equivalent for practical purposes, or am I missing
something? 

Brian.
On Thu, 16 Feb 2012 17:04:46 -0600, "Fender123"
<joeborg123@n_o_s_p_a_m.excite.com> wrote:

>May I ask one further clarification: what is different in the end result >using overlapped Goertzel, and sliding DFT? I mean apart from computational >resources. Aren't both equivalent for practical purposes, or am I missing >something? > >Brian.
For most implementations at every Nth output they're essentially the same. There's a difference in that in between the Nth outputs the Goertzel algorithm has an intermediate and potentially not useful result, but the sliding-window DFT will always have the output that represents the frequency coeficient for the last N input samples. Eric Jacobsen Anchor Hill Communications www.anchorhill.com