Some
other frequency control options
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New-fangled digital stuff just around the
corner:
A neat DDS kit: (August
2002) I now
have a Hands Electronics DDS3
module assembled and working - based on the AD9850 DDS, this puppy
gives
you 0-40 MHz RF with 1 Hz resolution, readouts, offsets, twin VFO's for
split, etc., etc. Kanga
used to carry the kits in the US, until Sheldon Hands retired to
Portugal! The kit's output is pretty clean on its own, but
will
still need a PLL/VCO setup for cleanest output. When comparing it with
10 MHz WWV, it starts about 30 Hz low, then after 10 minutes drifts
right
onto frequency - pretty good for being clocked with a simple canned 100
MHz oscillator!
A more bare-bones digital approach:
While looking for PLL blocks for the above, I found this neat little PLL
Experimenter's Kit, with a Motorola MC145170 PLL chip, keypad,
minimal
microprocessor, and prototyping area for your own VCO. It'll go
anywhere
in 10 kHz increments up to about 185 MHz. I was thinking of trying the
DDS3 as a variable reference for this.
Great digital experimenter's info: QRP
Quarterly had a
cool Digital QRP
Homebrewing column, with an evolving "digital
breadboard". Now under the banner of the American QRP Club, the system is
coming closer to reality: as of mid-March 2004, you can put in a
reservation for the
Micro908 Antenna Analyzer, which actually can be more than that
with just some new software. It's got several blocks on one board: a
68HC908AB32 microcontroller
programmable in-circuit, an AD9850 DDS daughterboard, LCD, rotary
encoder, keyboard input, paddle input, reflectometer and buffer amps,
and for future audio use, a DSP board. This could turn into a central
rig control center for me!
A superb stand-alone DDS VFO setup: the
"Melt-Solder
DDS Controller" takes one of those DDS daughterboards above and
adds an Atmel microprocessor to control it, drive an LCD, serve as a
keyer, and drive band-selection lines for your complete rig! Not
available as of mid-March 2004, I just got in on the first run, and it
may come available again.
How about a synthesizer with a "manual
transmission?" Just finished is the PLL module kit from
the multiPIG+ - http://www.kitsandparts.com/kits.html
... Sure, the microprocessor, knob, and LCD display of the DDS3 above
is
slick... but how about an approach where you get into the nuts and
bolts
of it when you tune around? Just use the Motorola MC145151P2
parallel-input
PLL chip, some hexadecimal input switches, a wide-range VCO, and a
varactor
tuned VXO for a variable reference, and you have a fun way to generate
a wide range of frequencies. The whole multiPIG+ idea is a cool
experimenter's radio to try - clean state-of-the-art circuitry but a
bunch of modules with no slick front panel - to change bands you plug
the jumpers around , set the PLL switches, etc - see the pictures here
to get the idea. Kind of like my haywired picture above...
Why is it called the multiPIG? Checkout the Flying
Pigs QRP Club....
Another quasi-synthesizer
which I haven't
tried: Another,
less expensive digital option is the Radio
Adventures CycleMaster
, a versatile frequency-locked loop
controller
with 10 Hz resolution, RIT, and 32 setup memories that will tune and
stabilize
any voltage-controlled oscillator. Just build your oscillator for the
desired
range, hook it up, and go. Under $100 for the controller kit, plus your
junk box parts for an oscillator.
Less range, but low power consumption: The FCC-1 and FCC-2 kit combo from the Norcal QRP Club
are a great option for portable rigs. The FCC-1 is a frequency counter
kit, through 50 MHz, with display offset capabilities. The FCC-2 is an
add-on that adds DDS VFO functionality, DC-20 MHz. Another one sitting
on the bench awaiting assembly time...
And the ultimate: For
as much as I paid for the Sheldon Hands kit years back, I can now get a
nice fancy QUADRATURE DDS-VFO - AA0ZZ's IQPro, available from Kanga US. Nice full controller, lots of buttons, band select outputs... the works. Have to wait a while on this one... |