[hpsdr] spectrum increased frequency resolution?

[John Melton]

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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