Sunday, 20 November 2011

Direct Digital Synthesiser (DDS 1 and 3)

These are the synthesisers that steer the phase locked oscillators. Their heart consists of an AD9850 which is a 125 MHz complete CMOS DDS from Analog Devices.

The DDS 1 Module, SLIM-DDS-107, is the fine frequency "steering" source for PLO 1 in the MSA.

 Finished DDS1. There's not much in there, you can see a 78L05 voltage regulator to the left, the AD9850 itself in the centre and a 10.7 MHz crystal filter to the right.

The filter is shielded from the rest of the circuit with a fence.

Bottom view. The SMA connectors are not placed yet as they weren't in the mail. Connectors in China are incredibly cheap but you have to live with up to 30 days of shipping...

 Both synthesisers and a couple of extra perimeter shields.

A few copper strips prepared for the shields

The first few attempts were crap but his frame is actually almost a perfect fit. I'm bending the strips with small pieces of PCB.

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