DDS may have their place but a transceiver VFO may not be one of them
for the present state of the art. They can display low phase noise but
over a broad background spectrum of coherent closely spaced spurs
accompanied by a few spurs with significant strength. They are improving
and using a smaller fraction of their possible frequency range sometimes
allows enough major spur free range for something like a Tentec VFO.
That can require using a UHF or 1 GHz clock and taking much care with
that clock to not introduce lots of phase noise with the on chip phase
locked loop multiplier with an inadequate loop filter.
One of the best references I know for them and for designs for ham gear
in general is the ARRL book titled Experimental Methods in RF Design,
ARRL number 9239, by Wes Hayward, W7ZOI, Rick Campbell, KK7B, and Bob
Larkin, W7PUA, radio
gurus of the highest order.
73, Jerry, K0CQ
On 11/26/2010 5:11 PM, Bwana Bob wrote:
I have seen ads in the radio magazines for a DDS VFO. It's not
advertised as a replacement for any current VFO, but it might do the
job. It would be an interesting science project.
73,
Bob WB2VUF
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