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Hi,

array processing / analog to digital cards

I would like to process signal from an antenna array with 8 elements.
Initially I was thinking of using an A/D card to digitize, with 8
input ports for 8 antenna array. Each antenna would have its cable
coming into each port (assuming no RF analog) on to the card

But recently a friend told me that a "multiplexer" can be used to
multiplex the 8 antenna signals into one and piped to a single port of
A/D card. That way a single port (cheaper) card could be used and less
hassle with cabling.

Assuming the bandwidth to be received/processed is 30 Mhz and the A/D
is 70Mhz, can someone pls guide me:

1. Can such processing be done using multiplexers?
What are the drawbacks in terms of losing signal info, etc.

2. What are the important specs/considerations when dealing with
multiplexers in such a setup?

3. Can you recommend a brand?

4. If multiplexers are not useable, can you suggest a cheaper
alternative to buying a 8 port A/D card with 8 a/d chips, etc.

Thanks

Russ


You seem to think that the multiplexer approach will give you something for
nothing - it won't. If you replace eight 70MHz A/Ds with one A/D and an
8-input multiplexer you'll have to sample eight times faster - i.e. at a
rate of at least 480MHz. What is more, you will need a multiplexer that can
switch at 480MHz - i.e. spend only 2ns on each channel. In that time all
switching transients - and the signal itself - must settle and THEN, the A/D
perform the conversion.

Not mission impossible, but if you need to ask these questions, you might
find this project quite difficult.

John A