Resonant circuit design

[bitrex]

On 8/10/19 8:52 PM, Bill Sloman wrote:

On Saturday, August 10, 2019 at 6:31:55 PM UTC+10, Phil Hobbs wrote:
On 8/10/19 12:56 AM, Jan Panteltje wrote:
On a sunny day (Fri, 9 Aug 2019 18:06:17 -0400) it happened bitrex
user@example.net> wrote in <u7m3F.75406$3m1.70413@fx17.iad>:

it's slow enough freqs (MHz) that I can use some op amps.

74HC4046?
Works from 3V upwards.
Always have some in stock here.


Yeah, that part has about the crappiest oscillator in history.

The original 4046 oscillator worked over a large range of voltages, and the Philips 74HC and 74HCT didn't. The 74CT9046 did have an improved pahse detector.

In a VCO with a wide tuning range there are also second order effects I
assume, when delta f is not sufficiently <<< as compared to the resonant
frequency f of the tank.

I could do the math but I suspect it would tell me that the tuning range
is pessimistic as compared to calculations under the assumption that the
tank resonant frequency is a constant and no second-order effects apply.

 

[George Herold]

On Sunday, August 11, 2019 at 2:17:30 AM UTC-4, bitrex wrote:

On 8/10/19 8:52 PM, Bill Sloman wrote:
On Saturday, August 10, 2019 at 6:31:55 PM UTC+10, Phil Hobbs wrote:
On 8/10/19 12:56 AM, Jan Panteltje wrote:
On a sunny day (Fri, 9 Aug 2019 18:06:17 -0400) it happened bitrex
user@example.net> wrote in <u7m3F.75406$3m1.70413@fx17.iad>:

it's slow enough freqs (MHz) that I can use some op amps.

74HC4046?
Works from 3V upwards.
Always have some in stock here.


Yeah, that part has about the crappiest oscillator in history.

The original 4046 oscillator worked over a large range of voltages, and the Philips 74HC and 74HCT didn't. The 74CT9046 did have an improved pahse detector.


In a VCO with a wide tuning range there are also second order effects I
assume, when delta f is not sufficiently <<< as compared to the resonant
frequency f of the tank.

I could do the math but I suspect it would tell me that the tuning range
is pessimistic as compared to calculations under the assumption that the
tank resonant frequency is a constant and no second-order effects apply.

Ahh if you told us what you wanted (freq./ range/ amplitude /load. etc)
then you could get more help.

GH

 

[Clifford Heath]

On 10/8/19 2:39 am, bitrex wrote:

In e.g. VCO design, assuming a less than ideal varactor/varicap, is
there a particular resonant circuit/tank topology or ratio of components
where given a base operating frequency with no control voltage applied,
the VCO frequency deviation either side is maximized with respect to
change in varicap capacitance?

Not sure what you're asking exactly, but the Vakkar oscillator gets
about a 4:1 ratio from two varicaps. Google it up.

Clifford Heath.