VCO IC for HF

[W1RKW]

Anyone know of a VCO IC that will work in the HF region.  All the IC's I have come across operate in the VHF or higher range.

[KF1Z]

How about   74LS624  ?

I picked up a couple to play with.... though I haven't had time yet to try it out.

I think though, it may only be good up to 20mhz....
(I'm only interested in <4mhz anyway)

I can email you a data sheet if you want.... ( about 400kb pdf)

[W1RKW]

Looks like it could do the trick.  Were did you get yours?  Mouser and Digikey don't stock it.

How about   74LS624  ?

I picked up a couple to play with.... though I haven't had time yet to try it out.

I think though, it may only be good up to 20mhz....
(I'm only interested in <4mhz anyway)

I can email you a data sheet if you want.... ( about 400kb pdf)

[w3jn]

ANy of those ttl or CMOS VCO chips that use R/C frequency determining elements are gonna be unusable for much of anything except maybe as a signal generator.  The phase noise is ungodly high, and if you try and use it as an oscillator in a xmitter you're gonna create a lot of hate on the band.  If you use it as the LO in a receiver you won't hear much of anything except noise.

The 4066 PLL chip has a R/C VCO on it as well, it's good up to about 20 MHz I believe.

You can use the oscillator section of a NE602/SA602/SA612 as a VCO, just add a varactor as part of the L/C resonant circuit.  But in reality the oscillator part of the'602 is just one transistor on the chip.

The MC1648 is another L/C oscillator chip that you might want to consider.

[WA1GFZ]

My first upconversion receiver project had a MC1648 in the synthesizer. It was OK but not great.
 I like a grounded gate fet like U310 with a hunk of semiridged as a resonator. A LC will also work well at lower freqs. RC oscillators are very unstable.

[W1RKW]

thanks for the heads up. I read the data sheet it but wasn't sure if I'd be dealing with logic type levels or a sinewave. Plan B

[KF1Z]

Yeah......ok on the phase noise......
For my purposes (class-e) square wave is a good thing.....
But I'm sure excessive phase noise is not....

[w3jn]

Forget using a VCO as a VFO unless it's part of a synthesizer.  A free running VCO has WAY too much phase noise.

It's easy to build a nice stable VFO using a variable capacitor.  Buffer the output well and run that into a 74LS14 to square it up.  You can run some variable bias on the input of the '14 to vary the duty cycle.

[KF1Z]

That's basically what I have now....

A Hartly Osc, into a 74s112  (WA1QIX).
The case is padded for mechanical vibration, and out of the sun (for temperature stability),
after a minute or so, it stays pretty well on frequency.

The 74s112 drives the two DEIC420 mosfet driver ICs fairly well, but Steve has suggested using a pair of ixdd414 ICs as another buffer stage.
That's usable on 75 and 160...Osc runs in teh 7mhz range, and uses the divide by 2 (or 4) function of the 74s112 JK flip-flop to get the output frequency.

Guess I may as well stick with that for now, until a cheaper DDS kit is available.

[WA1GFZ]

S logic is old as dirt. Iout high sucks, Try AC logic much stronger output driver.
You will make a much cleaner square wave.

[w3jn]

That VFO was my design actually, I gave it to Steve.  Not that it matters.