DIYing an LF signal generator with phase modulation

[philpem]

Hi guys,

I'm doing some experimenting with LF radio navigation (specifically, Datatrak). I'm at a point where I'd like to generate a test signal...

What I'd like to do is generate a pair of LF signals (around 130-140kHz) with phase modulation. I need to modulate the phase at ~1kHz (1ms per step) or faster, ideally with ~1 millicycle (0.36 degree) phase resolution.

Both signals would go down the same cable to the RF In of the nav receiver.

I was thinking of using a pair of Analog Devices AD9837 DDS chips and a mixer stage (probably with a dual digital pot so I can vary the amplitude of the signal). Question is, is the phase noise of a DDS likely to cause me problems?

I need good frequency accuracy too -- the receiver uses a TCXO, an I'm planning to do the same.

Are there any other ways to generate a PSK signal with this kind of resolution?
The modulation is analog - part of the signalling involves phase-modulating the carrier with a 50Hz or 33Hz modulating signal to transfer data.

Thanks.