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Re: [Discuss-gnuradio] diminishing returns with increasing frequency off

From: Martin Braun
Subject: Re: [Discuss-gnuradio] diminishing returns with increasing frequency offset
Date: Thu, 17 Mar 2016 11:33:12 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1

What's your sampling rate? The further you go towards the edge of your
Nyquist zone, the more the anti-aliasing filter might be kicking in.


On 03/17/2016 10:23 AM, tom x wrote:
> Hi,
> My setup is a USRP N210 receiving from a transmitter sending a few
> packets a second. (The packets are decoded with Bloessl's 802.15.4 PHY
> block if it matters)
> Let's say the transmitter is sending data on frequency f_t.
> I set the USRP to receive on f_t plus an offset f_o.
> The next block is a frequency xlating FIR filter centered at -f_o.
> This is intended to correct the offset.
> I made a slider block for f_o and allowed it to vary between 0 and 3MHz.
> I need an offset of a few MHz for my application. However, the number of
> packets received seems to drops as I increase f_o. I get almost no
> packets after f_o is increased over 0.5MHz.
> The overall purpose of this is to carve two channels out of the received
> bandwidth with two frequency xlating FIR filter blocks, with the USRP
> tuned between the channels and the filter blocks centered at offsets
> that put them on the channel peaks. As explained above, if the offset is
> too big, it stops working. Why do you think this is happening?
> Thanks,
> Tom
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