Contents :

A collection of thoughts, and my notes about experiments and ideas, technical or otherwise, connected to Amateur Radio, Satellite working and monitoring and other electronics.

Sunday, June 13, 2010

Enter the DDS

Just received a kit, the DDS-2 from N3ZI.

The kit contains all parts, including a simple display, for making a functional DDS.

The kit is relatively easy to assemble, all parts were present. The SMD integrated DDS chip is somewhat more tricky to solder without creating solder bridges. I think the pads are a bit wider than the pads for the NE612 SMD mixer on the Rockmite/Warbler kits from Small Wonder Labs.

First the bad news : Tuning the DDS-2, as it is, is an exercise in patience. it is slow, when trying to use the fast function (turning the knob faster), the tuning becomes erratic. The lack of a keyboard entry function is serious with such a slow tuning.

It looks like a modification of the firmware should be attempted. Quite a daunting task, given that (as far as I know) the source code is not available, and my programming skills are not that good.

The good news is that the temperature stability looks fine. the crude "switching on and off the fan" method revealed about 20 - 25Hz drift on 10 MHz, of course relatively less on lower frequencies. For a non- temperature compensated clock oscillator this feels quite good, and I would expect better stability when the DDS is boxed.

Other good new on the DDS-2 : even if tuning is a bit of a pain, there are two redeeming qualities :

- the standard firmware has 10 "memories", acting like the "Band stacking" feature of many modern transceivers. so a multi frequency MEPT with 10 (11) pre-programmed frequencies is quite doable

- the application of the RIT should be quite useful for generating FSK easily, eg for a relatively frequency agile MEPT.

However, for more experiments I did order a DDS60 daughterboard that should be programmable from a PC or an external (PIC, PICAXE etc) microprocessor board.

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