"dave.harper" wrote in message
ups.com...

Good info to know. I was kinda looking around to make a (mostly) IC
transmitter like that... (anything 70cm and under). Are you aware of
any chip PN's or schematics I could dive into to learn?

Analog Devices' parts are favored by hams. The greatest number of projects
out there use the AD9850, but that part is a little older, and does not
provide modulation input. Also, it is really only good up to about 30 MHz,
you can push a bit past that but the power requirements explode and the
noise goes up. Without any component changes it will go down to 1 Hz.
Newer AD98xx parts are starting to get more attention, and some of those are
useful up into the low 100's of MHz. The 99xx parts have more features yet.

TI has a TRF4400 which is a 440 MHz synthesizer with modulation and an amp
(not much of an amp, tho!), and the almost identical 4900 for 900 MHz. Some
folks have used these down to 6 meters. The TI parts have greater channel
spacing than the AD parts, but that also reduces the frequency of the
crystal or oscillator, which has a big effect on the power consumption. TI
also has a 2050/1/2 which are synthesizers (I don't recall if they have
modulation) up into the gigahertz range. I've been toying with using one of
the TI parts as a VFO for an HF rig by using a prescaler to divide down the
frequency (and consequsntly the spacing).

The AD parts are pricey, but AD is very good about samples. The TI parts
are all in the five buck neighborhood. There are a zillion projects/kits
out there based on the AD parts.

If you've ever built an analog VFO, these DDS parts are like black magic.
They take little in the way of support circuitry, no fretting about layout,
no spending weeks trying to work out the temperature compensation, no moving
around because you breathed on it, you just dial in the frequency you want
and you are spot on.

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