EMRFD Message Archive 8511

Message Date From Subject
8511 2013-04-11 22:09:06 yz1gw Design tracking PLL, help
Hi Wes and group,

I'm trying to make a PLL VFO for my phasing DC receiver. I tried PLL design with 74hc4046, but i have loop oscillation problem.

I would like to try similar design to offset tracking PLL with 74HC74 detector, from EMRFD fig 4.42, 4.45 and 4.57A, but I need help for specific loop filter components ("TBD" components from fig 4.57A).

My goal is:

VCO range: 28 to 28.4 MHz
VCO gain: 120kHz/V (measured)
VFO range: 4 to 4.4 MHz
I will use OP AMP TL072 (i have not OP027)

I would be grateful if someone could help.

73 de YT5RA
Djole
8539 2013-04-15 12:02:44 Wes Re: Design tracking PLL, help
Hello Djole and group,

I have also had problems with the 74hc4046 and loop stability. I didn't pursue it very far.

I have added a PLL design aid on my web site. This is a program within a Zip file, so it can be downloaded. Just go to http://w7zoi.net/ and then to the emrfd errata section. Then look at the book related items where you can click
8540 2013-04-15 12:25:03 Lasse Moell Re: Design tracking PLL, help
Years ago I did some PLL design with the 74HC4046.. what I had problems
with was the dead-zone where the phase detector goes into hi-z mode and
the gain changes. The remedy was to have a 1Mohm resistor on output to
draw current all the time. This worsen the phase noise a bit but made
the loop much much more stable.

One other thing that may cause problems is when one uses an active loop
filter, the op-amp may have stability issues if input voltage is too
high.

/Lasse SM5GLC

On 15 apr 2013 21:02 "Wes" <wesw7zoi@gmail.com> wrote:

>
>
> Hello Djole and group,
>
> I have also had problems with the 74hc4046 and loop stability. I
> didn't pursue it very far.
>
> I have added a PLL design aid on my web site. This is a program within
> a Zip file, so it can be downloaded. Just go to <http://w7zoi.net/>
> and then to the emrfd errata section. Then look at the book related
> items where you can click
8541 2013-04-15 12:50:43 William Carver Re: Design tracking PLL, help
I think it was Philips who otroduced a version of 4046 that didn't have
that dead zone. I think that's now the NXP 74HCT9046A. I'm not sure how
much that might have increased the phase detector spur in the output.

W7AAZ


On Mon, 2013-04-15 at 21:25 +0200, Lasse Moell wrote:
>
> Years ago I did some PLL design with the 74HC4046.. what I had
> problems
> with was the dead-zone where the phase detector goes into hi-z mode
> and
> the gain changes. The remedy was to have a 1Mohm resistor on output to
> draw current all the time. This worsen the phase noise a bit but made
> the loop much much more stable.
>
> One other thing that may cause problems is when one uses an active
> loop
> filter, the op-amp may have stability issues if input voltage is too
> high.
>
> /Lasse SM5GLC
>
> On 15 apr 2013 21:02 "Wes" <wesw7zoi@gmail.com> wrote:
>
> >
> >
> > Hello Djole and group,
> >
> > I have also had problems with the 74hc4046 and loop stability. I
> > didn't pursue it very far.
> >
> > I have added a PLL design aid on my web site. This is a program
> within
> > a Zip file, so it can be downloaded. Just go to <http://w7zoi.net/>
> > and then to the emrfd errata section. Then look at the book related
> > items where you can click
8542 2013-04-15 16:49:04 kb1gmx Re: Design tracking PLL, help
8544 2013-04-15 18:02:01 rlramirez77 Re: Design tracking PLL, help
Has anyone had similar experiences with the Motorola MC14046BCP part? Only asking because this version is a bit different than the CD4xxx or 74HC4xxx parts.

Russ
K0WFS

8546 2013-04-15 18:02:02 Dana Myers Re: Design tracking PLL, help
8551 2013-04-15 18:36:06 Chris Trask Re: Design tracking PLL, help
>
>> Years ago I did some PLL design with the 74HC4046.. what I had problems
>> with was the dead-zone where the phase detector goes into hi-z mode and
>> the gain changes. The remedy was to have a 1Mohm resistor on output to
>> draw current all the time. This worsen the phase noise a bit but made
>> the loop much much more stable.
>>
>> One other thing that may cause problems is when one uses an active loop
>> filter, the op-amp may have stability issues if input voltage is too
>> high.
>>
>
>Has anyone had similar experiences with the Motorola MC14046BCP part? Only asking because this
> version is a bit different than the CD4xxx or 74HC4xxx parts.
>

This is a situation where you might want to consider using the XOR phase detector (PC1out). It's essentially a quadrature phase detector. They work fine as long as your tracking bandwidth is less than an octave.


Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/
8555 2013-04-16 02:34:08 Lasse Moell Re: Design tracking PLL, help
I found it easier to use the old MC4044 and the faster sibling MC12040
rather than trying to push a 4046 into service at a high reference
frequency.

Today I would look into some more modern circuits from Analog Devices or
similar.

/Lasse


8563 2013-04-19 07:43:05 yz1gw Re: Design tracking PLL, help
I thank you all for the helpful information, especially Wes for software which helped me a lot.

I constructed PLL (ugly style) and it worked from the first time. Since I have no sophisticated instruments to check for phase noise, I used another receiver to listen to the VCO and I was very pleased with results, noise was much lower then with 4046 PLL. Second, when I connected VCO/PLL to my phasing receiver, listening to the strong transmitter signal(on dummy load), I did not noticed any PLL problem/harsh on the whole band.

My VFO is stabilized with Huff&Puff and frequency stability is excellent.

After this experience, I have many new ideas...

73, Djole / YT5RA