Other VFO's

by John Seboldt, K0JD, 
Milwaukee, WI

Last update: 9/7/06

Some other frequency control options

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....fpqrp

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...

John's Mugshot

John Seboldt, K0JD, Milwaukee, WI
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