Re: [Discuss-gnuradio] AR5000 and downconversion

[Alan Gray]

Sorry, I probably should have been more specific about my aims

I'm looking to receive and demodulate an Australian HDTV signal. We use a 
COFDM (Coded Orthogonal Frequency Division Multiplexing) modulation scheme 
instead of the ATSC scheme used in the US but the bandwidth requirements 
are approximately the same, around 6-7MHz. This, I believe, rules out the 
possibilities of trying to use undersampling techniques to sample the 
signals, as I don't think I can fit the entire signal into a Nyquist region.

I'm looking at trying to downconvert the 10.7MHz IF to a center somewhere 
in the range of 5-6MHz, which I think should be possible though I'm 
currently unsure if there is an IC on the market which will do the job 
while still maintaining a decent IF bandwidth. I'm still looking into the 
possibilities, but again, if anyone has an opinion it's most welcome

Alan



At 07:58 AM 14/05/03 -0700, you wrote:

> Alan,
>
> I thought that many of the applications for SDR had baseband bandwidths on 
> the order of 10MHz... how low of an IF are you looking for?  Check out the 
> datasheet for the max2450 (http://www.maxim-ic.com/max2450) -- its an I/Q 
> mod/demod, but its set up for a 70MHz IF, so it won't work here.
>
> I'm looking into a zero-IF solution, but it seems like a 10.7MHz IF 
> solution makes your 20Msps ADC _almost_ good enough -- how much margin 
> over Nyquist are you looking for?  It just seems too easy to stick with 
> 10.7 since LOs, filters, etc are sooooo cheap. I take it you really like 
> your ADC?
>
> Brian.
>
> On Wednesday, May 14, 2003, at 06:52 AM, Alan Gray wrote:
>
> > Hi all,
> >
> > I've recently found that I have access to several standard radio
> > receivers,
> > including an AOR AR5000 and AR8600. Naturally, these both have a 10.7MHz
> >
> > output IF and thus aren't much use in combination with my 20MSPS A/D
> > card
> > but I was wondering if anyone has looked into the possibility of adding
> > an
> > extra downconversion stage after this to obtain a usable IF.
> >
> > I haven't much experience in dealing with the radio side of things, but
> > a
> > quick look at some books on the subject seem to indicate that it might
> > not
> > be too hard a circuit to put together. If anyone has looked into doing
> > this
> > or has ideas on if it will/will not work, any information would be most
> > welcome
> >
> > Alan
> >
> > <ATT645869.txt><ATT645870.txt>
>
>
>
>
>
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