EMRFD Message Archive 9227

Message Date From Subject
9227 2013-10-08 18:53:09 bob_ledoux Using 74HC04 as VFO
I'm looking at QST, 2/2005, page 32, "The W6QIF Oscillator."  The article discusses use of varicaps, and back-to-back 1N4005 diodes as tuning caps in an oscillator based on a 74HC04 inverter chip. 

I'm interested in his selection of the 74HC04 chip.  He also describes his circuit as a Vackar oscillator, which suggests it is a low drift circuit.

 What experience do we have in building square wave LC VFO's using such a digital chip?

 I've seen numerous schematics using the inverter chip as a crystal oscillator for digital applications.

Are there reasons why this application isn't more common?
9228 2013-10-08 19:59:39 Dana Myers Re: Using 74HC04 as VFO
9229 2013-10-09 07:24:16 WA0ITP Re: Using 74HC04 as VFO

In his article W6QIF mentions that the TC of the -6 mix toroid he used went negative after boiling it.  Interesting, how can that happen?
Real radios weigh less than a pound.
I love this radio stuff !
72   WA0ITP
----- Original Message -----
9235 2013-10-11 09:54:14 mosaicmerc Re: Using 74HC04 as VFO
9237 2013-10-12 09:18:43 ehydra Re: Using 74HC04 as VFO
mosaicmerc schrieb:
> What do u guys think of this item:
> http://www.newark.com/jsp/search/productdetail.jsp?sku=29H0701
> That series include fast D flipflops which can give frequency division. I am thinking of making a custom oven controlled oscillator based around a 100 or 200Mhz crystal with this logic.
> Do you think 200Mhz is reasonable with this logic circuit?

Yes. Maybe not over full temperature range and lowest VCC, but at 3.3V
and 0 to 70°C no prob.

- Henry

9238 2013-10-12 11:39:04 Gene Dorcas Re: Using 74HC04 as VFO

See how fast it will go and more important is it stable???  Let us know.


Gene, W5DOR