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Re: [linrad] Mixer design - comments please

Hi Alex,

Since the input range of some soundcards can be in the range of 10 vpp, it 
may be better to use a 10V supply for the Op-Amps. You may also consider 
using the NE5532 instead of the NE5534 to lower the component costs.

What type of LO source are you planning in building? 

Looking at the DDS schematics presented in the SDR-1000 article, I don't
understand why Gerald used lowpass filters and than a comparator if the
DDS already has a square I/Q output.


-- Edson, 7n4ncl

On Mon, 7 Jul 2003, Alex Crow wrote:

> Hi All,
> With the help of some very good chaps on this list I am now comitted to 
> working on a General Coverage receiver to work with Linrad in the I/Q mode, 
> to receive SSB and AM, both amateur and broadcast. My design is based largely 
> on the SDR-1000 articles, and I have just finished the design of what should 
> be the Tayloe Detector part.
> I have replaced the (too expensive) Instrumentation amps with a cascade of 
> NE5534's, and have (tentatively) reworked for a single +5V supply. What I 
> would like is for you chaps to have a look at my circuit and make any 
> criticisms and reccomendations you see fit: I only have enough resources at 
> the moment to make one board for each part and would like them to work first 
> time! BTW, I am using Eagle for the CAD of these bits.
> If you feel I should give the Op-Amps a 10V supply please tell me, and if you 
> can explain why the input bias to the Tayloe detector in the SDR-1000 seems 
> to be 1V, when the Instr. Amps have the whole 10V to play with!
> The url for the schematic  is:
> http://home.clara.net/alexcrow/mixer.png
> I can also put the Eagle files up there if anyone is interested.
> BTW, I know I need some electolytics on the ouput to the soundcard!
> Thanks  muchly in advance,
> Alex