[sdiy] HF VCOs and tracking problems

[Richie Burnett]

I'd put in a good word for Direct Digital Synthesis (DDS) technology.

DDS chips are cheap, give outstanding frequency linearity, allow you to set 
the frequency to mHz resolution from DC to MHz frequencies, can change 
frequency at the drop of a hat with no "settling time" and the output drift 
spec is as good as the crystal you use for the master oscillator!  These are 
gradually replacing PLLs in conventional frequency synthesiser applications 
because of their improved frequency agility and fine frequency resolution. 
They're also easier to set up than a PLL - No messing about with loop 
filters, stability calculations etc.

The only downside might be that you have to program in the frequency 
digitally over SPI.  This might complicate your application if it's all 
analogue so far.

-Richie,

----- Original Message ----- 
From: "Karl Ekdahl" <elektrodwarf at yahoo.se>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, November 13, 2012 10:10 PM
Subject: Re: [sdiy] HF VCOs and tracking problems


Okay there's a lot of good suggestions here. Yeah i'm trying to avoid the 
PLL stuff as i want both low parts count and i want to avoid the settling 
time. This is for testing some divide-down stuff so i need all of the usual 
properties of a VCO. I'm going to give the OTA triangle core a shot and see 
how good tracking i can get. I'll probably be back with more questions. 
Thanks a lot everyone!

Karl