[hpsdr] spectrum increased frequency resolution?

[Frank Brickle]

John --

No, there's more information there; but it's not necessarily what one thinks
it is -- or better, it demonstrates that what you're looking for isn't
exactly increased spectral resolution, although that's part of what you
want. But I don't think anybody here is exactly interested in a technical
discussion of all that right now. More interested in getting something that
works.

The thing to look for is a writeup on the Yule-Walker method. It involves
computing a set of coefficients on each frame of sample data which can then
be evaluated on an arbitrary frequencies grid for high-resolution estimates.
There's a writeup in the Spectral Analysis book I referred to last night,
but there's also a reference implementation in any of the Numerical Recipes
books.

73
Frank
AB2KT

On Tue, Jun 9, 2009 at 5:12 AM, John Melton <John.Melton at sun.com> wrote:

> ***** High Performance Software Defined Radio Discussion List *****
>
> I have been looking at this for a while and I don't think that extending
> the FFT and padding with zeros will give you the resolution you are hoping
> for on the bandscope.
>
> I think to get better resolution on the bandscope we need to have some help
> from Mercury.
>
> I have modified ghpsdr to have the FFT use 32768 samples (4096 actual
> samples and the rest padded with zeros).  This allows me to do a 16X zoom on
> the bandscope (i.e. I can see 3840 KHz) where I get a 1:1 sample/pixel
> display.  You really cannot see much additional information. It is simply
> the original display stretched out.  After all, it only had 4096 samples to
> start with.
>
> I have committed the code into the svn store if anyone is interested.
>
> Regards,
>
> John g0orx/n6lyt
>
>
> On 06/09/09 00:35, Frank Brickle wrote:
>
>> ***** High Performance Software Defined Radio Discussion List *****
>>
>>
>>
>> ------------------------------------------------------------------------
>>
>> Stuff the samples into a longer FFT and pad with zeros.
>>
>> Remember, though, that what you gain in frequency resolution you lose in
>> time resolution. That's Heisenberg Uncertainty.
>>
>> You also have to be a little careful about how you window the data. Google
>> is your friend.
>>
>> 73
>> Frank
>> AB2KT
>>
>> On Mon, Jun 8, 2009 at 5:57 PM, David McQuate <mcquate at sonic.net <mailto:
>> mcquate at sonic.net>> wrote:
>>
>>    ***** High Performance Software Defined Radio Discussion List *****
>>
>>    If I have a block of samples (say N = 4096, fs = 122.88 Msps),
>>    a straightforward FFT produces data with frequency resolution of 30kHz.
>>
>>    Is there a technique that will allow me to obtain information on a
>> finer
>>    frequency grid (say 1kHz or 300Hz or ...)--other than "simply"
>> acquiring
>>    additional data, extending the length of the time record?
>>
>>    I've looked at Chirp-Z transforms and polyphase decimation, but neither
>>    seems to produce higher frequency resolution.  I've also looked into
>>    DttSP,
>>    but not found a solution there.
>>
>>    Am I hoping for the impossible?
>>
>>    Suggestions please.
>>
>>    73,
>>    Dave
>>    wa8ywq
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>>
>> --
>> ...although production beyond capacity is a contradiction in terms, it is
>> observed every day in academia. -- Frank Knight
>>
>>
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