Re: [Discuss-gnuradio] SDR question

Thanks Marcus

So you can go outside the useable bandwidth, you just need to understand
that you will loose something as you move to the next chunk of RF ?

I saw an image of several MHz and a little decode window, but I guess that
is a decoding window, smaller than the SDR sampling window.

I want to use SDR for satellites and packet radio

Does it meet a tnc / analogue radio specs ?

- Andrew -

----- Original Message -----
From: "Marcus D. Leech" <mleech@ripnet.com>
To: <discuss-gnuradio@gnu.org>
Sent: Saturday, October 29, 2011 7:16 AM
Subject: Re: [Discuss-gnuradio] SDR question

> On 28/10/2011 5:08 PM, Andrew Rich wrote:
>>
>> I have a question about software defined radio
>>
>> I saw a pass band the other day on a screen which prompted me to ask
>>
>> The Software defined radio has a specific bandwidth ?
>>
>> Does it "scan" across the band very quickly to form the passband, or is
>> the bandwidth already that large it just appears as a chunk of MHz ?
>>
>> I am trying to make the connection between how a Software Defined Radio
>> would be different from an analogue system.
>>
>> For example decoding packet radio using an SDR, is there any performance
>> degradation due to the way it works ?
>>
>> Would the SDR "sweep" and miss some of the signal ?
>>
>> - Andrew VK4TEC -
>>
>
> A typical SDR hardware front-end (just taking the RX view for now) has a
> tunable direct-conversion down-converter that converts a swath of
> bandwidth at a desired center frequency into a complex (I,Q) baseband
> signal that "straddles" from -BW/2 to BW/2,
> with "DC" in the middle.
>
> That swath of (analog) bandwidth is sampled by an ADC and FPGA, and then
> decimated for delivery of a lesser bandwidth (again, in complex
> baseband form) into the host computer for further processing. The
> decimation also acts as a filter, so that there is strong alias
> suppression
> in the delivered bandwidth. It is usually the case that the FPGA
> decimator is configurable with respect to the amount of bandwidth
> delivered towards the host.
>
> Bandwidths of several MHz into the host are achievable these days, with
> all demodulation, etc, happening on the host.
>
> That is not to say that you couldn't implement a sweeper for doing SIGINT
> and spectral estimation, etc. In fact, there are Gnu Radio
> applications that do just that.
>
>
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