John --<br><br>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.<br>
<br>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.<br>
<br>73<br>Frank<br>AB2KT<br><br><div class="gmail_quote">On Tue, Jun 9, 2009 at 5:12 AM, John Melton <span dir="ltr"><<a href="mailto:John.Melton@sun.com">John.Melton@sun.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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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.<br>
<br>
I think to get better resolution on the bandscope we need to have some help from Mercury.<br>
<br>
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.<br>
<br>
I have committed the code into the svn store if anyone is interested.<br>
<br>
Regards,<br>
<br>
John g0orx/n6lyt<div class="im"><br>
<br>
<br>
On 06/09/09 00:35, Frank Brickle wrote:<br>
</div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div class="im">
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Stuff the samples into a longer FFT and pad with zeros.<br>
<br>
Remember, though, that what you gain in frequency resolution you lose in time resolution. That's Heisenberg Uncertainty.<br>
<br>
You also have to be a little careful about how you window the data. Google is your friend.<br>
<br>
73<br>
Frank<br>
AB2KT<div class="im"><br>
<br>
On Mon, Jun 8, 2009 at 5:57 PM, David McQuate <<a href="mailto:mcquate@sonic.net" target="_blank">mcquate@sonic.net</a> <mailto:<a href="mailto:mcquate@sonic.net" target="_blank">mcquate@sonic.net</a>>> wrote:<br>
<br>
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If I have a block of samples (say N = 4096, fs = 122.88 Msps),<br>
a straightforward FFT produces data with frequency resolution of 30kHz.<br>
<br>
Is there a technique that will allow me to obtain information on a finer<br>
frequency grid (say 1kHz or 300Hz or ...)--other than "simply" acquiring<br>
additional data, extending the length of the time record?<br>
<br>
I've looked at Chirp-Z transforms and polyphase decimation, but neither<br>
seems to produce higher frequency resolution. I've also looked into<br>
DttSP,<br>
but not found a solution there.<br>
<br>
Am I hoping for the impossible?<br>
<br>
Suggestions please.<br>
<br>
73,<br>
Dave<br>
wa8ywq<br>
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