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Fwd: Re: [Discuss-gnuradio] USB2 <-> fast ADC & DAC

From: Alan Gray
Subject: Fwd: Re: [Discuss-gnuradio] USB2 <-> fast ADC & DAC
Date: Tue, 03 Jun 2003 23:43:26 +1000

Further to this discussion, I've been wondering how difficult it is to deal with signals which are sampled in the even nyquist zones and thus have their phase reversed in the spectral sense.

Is processing the signal going to be more difficult than a situation in which the signal is sampled in an odd zone, and is not reversed? Is there anything I should specifically look at to aid in processing?

I ask because I have contacts within Panasonic here in Australia who are willing to supply me with Microtune 4702 DT5 tuners free of charge. These tuners are similar to the 4937 being used by others, but have an IF output at 36MHz and bandwidth of 8MHz. This signal is fully contained within the 4th Nyquist zone when sampling at 20MSamples per second, so it should be viable to undersample it. My only concern is that it might be more difficult to process a complex signal with it's phase reversed.

I have over 140 of these tuners sitting in a box at University, Panasonic evidently bought a bunch of them and have no further use for the leftover units and are looking to off load them to a good cause, so there is some incentive for finding a good use for them. If these are in any why useful for this project, let me know, apparently they've got another 500 or so that they're looking to get rid of.

As always, any thoughts or suggestions are welcome

At 04:13 PM 30/05/03 -0600, you wrote:

At 3:07 AM +0100 5/30/2003, Henrique Miranda wrote:
>After some calculations I came with the following procedure:
>1: The Nyquist region can be obtained using n = floor(fc/B + 1/2)
>   where floor(x) rounds x towards minus infinity, fc is the
>   IF center frequency and B the signal bandwidth.
>2: The minimum fs can then be easily obtained by fs = (2*fc+B)/n
>3: If the optimum fs is intended use fs = 4*fc/(2*n-1) instead.
>Moreover, if (fc/B + 1/2) is an integer, then minimum fs equals
>the optimum fs.
>If you find some inconsistency in this procedure please let me know.

Dear Henrique,

No inconsistencies found. I had to brush up on my algebra of inequalities (aarghh!) but I agree with your equations #1 & #2. Nicely done and thank you again.

However, I must admit that I still don't fully appreciate what qualities make a particular fs "optimum".

Best regards,
Joseph A. DiVerdi, Ph.D., M.B.A.
http://xtrsystems.com/          970.980.5868 (voice)
PGP Key ID: 0xD50A9E33

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