Pulling frequency or spread spectrum of Colpitts osc

[Klaus Kragelund]

Hi

I have a Colpitts osc that is giving me a headache in radiated EMI

If I could pull the frequency at 100Hz so the energy is spread out, it could solve my problem

Sort of like this:

https://www.researchgate.net/publication/251979186_Simulation_and_implementation_of_improved_chaotic_Colpitts_circuit_for_UWB_communications

It looks like they use the inherent properties of the transistor to make a chaotic signal

I am using a standard BC847, so cannot do this

Anybody have an idea how to pull the frequency, cheap?

Sort of like an varicap across the tank caps, but varicaps are not cheap?

Cheers

Klaus

 

[Phil Hobbs]

On 2020-01-06 09:01, Klaus Kragelund wrote:

Hi

I have a Colpitts osc that is giving me a headache in radiated EMI

If I could pull the frequency at 100Hz so the energy is spread out,
it could solve my problem

Sort of like this:

https://www.researchgate.net/publication/251979186_Simulation_and_implementation_of_improved_chaotic_Colpitts_circuit_for_UWB_communications

It looks like they use the inherent properties of the transistor to
make a chaotic signal

I am using a standard BC847, so cannot do this

Anybody have an idea how to pull the frequency, cheap?

Sort of like an varicap across the tank caps, but varicaps are not
cheap?

Cheers

Klaus

Crystal or LC?

You might be able to FM a bit by changing V_CE.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

On Mon, 6 Jan 2020 06:01:28 -0800 (PST), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

Hi

I have a Colpitts osc that is giving me a headache in radiated EMI

If I could pull the frequency at 100Hz so the energy is spread out, it could solve my problem

Sort of like this:

https://www.researchgate.net/publication/251979186_Simulation_and_implementation_of_improved_chaotic_Colpitts_circuit_for_UWB_communications

It looks like they use the inherent properties of the transistor to make a chaotic signal

I am using a standard BC847, so cannot do this

Anybody have an idea how to pull the frequency, cheap?

Sort of like an varicap across the tank caps, but varicaps are not cheap?

Cheers

Klaus

What's your frequency? How far above spec limits is your EMI? In what
measurement bandwidth? In other words, how much do you need to sweep?

As Phil says, frequency will depend on supply voltage.

And all diodes are varicaps. Most ceramic caps are varicaps too.

Either way, you'd need a low frequency oscillator or equivalent to
sweep the oscillator frequency.

Is there a uP port pin available? You can have fun lowpass filtering a
pseudoramdom bit stream.





--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

On Monday, 6 January 2020 15:56:45 UTC, jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass filtering a
pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being jittered
by the pseudorandom bit stream...

John

 

[John Larkin]

On Mon, 6 Jan 2020 10:18:57 -0800 (PST), jrwalliker@gmail.com wrote:

On Monday, 6 January 2020 15:56:45 UTC, jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass filtering a
pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being jittered
by the pseudorandom bit stream...

John

It's interesting to consider making truly random bit streams from a
small uP. It needs an external source of entropy.

One idea is to pull down a tri-state pin and let it charge back up
into the same, or another input pin, logic or an ADC input. That
generates a sorta random time delay or number. Stir that into the guts
of a pseudorandom sequence generator or several.

--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[piglet]

On 06/01/2020 14:01, Klaus Kragelund wrote:

Hi

I have a Colpitts osc that is giving me a headache in radiated EMI

If I could pull the frequency at 100Hz so the energy is spread out, it could solve my problem

Sort of like this:

https://www.researchgate.net/publication/251979186_Simulation_and_implementation_of_improved_chaotic_Colpitts_circuit_for_UWB_communications

It looks like they use the inherent properties of the transistor to make a chaotic signal

I am using a standard BC847, so cannot do this

Anybody have an idea how to pull the frequency, cheap?

Sort of like an varicap across the tank caps, but varicaps are not cheap?

Cheers

Klaus

If you can tolerate AM and the colpitts is high enough frequency you can
modulate the oscillator transistor capacitances by injecting some wobble
into it's base. Or instead of a costly varicap across the tank use a
second vanilla BC847 across the tank either varicapping C-B or B-E
junctions or as an old school reactance modulator (should be findable
online).

piglet

 

[Cursitor Doom]

On Mon, 6 Jan 2020 21:58:41 +0000, piglet <erichpwagner@hotmail.com>
wrote:

If you can tolerate AM and the colpitts is high enough frequency you can
modulate the oscillator transistor capacitances by injecting some wobble
into it's base. Or instead of a costly varicap across the tank use a
second vanilla BC847 across the tank either varicapping C-B or B-E
junctions or as an old school reactance modulator (should be findable
online).

He hasn't stated if he's using a xtal or just LC. If it's the former,
there's much less latitude to pull the frequency.
--

"The BEST Deal is NO DEAL"

 

[John S]

On 1/6/2020 12:24 PM, John Larkin wrote:

On Mon, 6 Jan 2020 10:18:57 -0800 (PST), jrwalliker@gmail.com wrote:

On Monday, 6 January 2020 15:56:45 UTC, jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass filtering a
pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being jittered
by the pseudorandom bit stream...

John

It's interesting to consider making truly random bit streams from a
small uP. It needs an external source of entropy.

One idea is to pull down a tri-state pin and let it charge back up
into the same, or another input pin, logic or an ADC input. That
generates a sorta random time delay or number. Stir that into the guts
of a pseudorandom sequence generator or several.

What about taking the audio output of a radio tuned off-station as an
input to a processor for random numbers?

 

[Klaus Kragelund]

On Monday, January 6, 2020 at 3:29:21 PM UTC+1, Phil Hobbs wrote:

On 2020-01-06 09:01, Klaus Kragelund wrote:
Hi

I have a Colpitts osc that is giving me a headache in radiated EMI

If I could pull the frequency at 100Hz so the energy is spread out,
it could solve my problem

Sort of like this:

https://www.researchgate.net/publication/251979186_Simulation_and_implementation_of_improved_chaotic_Colpitts_circuit_for_UWB_communications

It looks like they use the inherent properties of the transistor to
make a chaotic signal

I am using a standard BC847, so cannot do this

Anybody have an idea how to pull the frequency, cheap?

Sort of like an varicap across the tank caps, but varicaps are not
cheap?

Cheers

Klaus


Crystal or LC?

it's LC

You might be able to FM a bit by changing V_CE.

Yes. I also tried loading the center cap point with variable resistance, and I can pull the frequency by doing that

Cheers

Klaus

 

[Klaus Kragelund]

On Monday, January 6, 2020 at 4:56:45 PM UTC+1, jla...@highlandsniptechnology.com wrote:

On Mon, 6 Jan 2020 06:01:28 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

Hi

I have a Colpitts osc that is giving me a headache in radiated EMI

If I could pull the frequency at 100Hz so the energy is spread out, it could solve my problem

Sort of like this:

https://www.researchgate.net/publication/251979186_Simulation_and_implementation_of_improved_chaotic_Colpitts_circuit_for_UWB_communications

It looks like they use the inherent properties of the transistor to make a chaotic signal

I am using a standard BC847, so cannot do this

Anybody have an idea how to pull the frequency, cheap?

Sort of like an varicap across the tank caps, but varicaps are not cheap?

Cheers

Klaus

What's your frequency? How far above spec limits is your EMI? In what
measurement bandwidth? In other words, how much do you need to sweep?

The frequency is 20MHz. The test receiver for radiated emissions has 120kHz bandwidth, so to move it out of band, I need about 1% deviation, just to get 6dB reduction

Right now I am about 15 dB above the limits

As Phil says, frequency will depend on supply voltage.

And all diodes are varicaps. Most ceramic caps are varicaps too.

Either way, you'd need a low frequency oscillator or equivalent to
sweep the oscillator frequency.

Is there a uP port pin available? You can have fun lowpass filtering a
pseudoramdom bit stream.

Yes. I have a microcontroller on board, so I can use that to modulate the frequency. Although I would like a self running device, I have 2 IO pins that could be used for that purpose

Cheers

Klaus

 

[Klaus Kragelund]

On Monday, January 6, 2020 at 10:58:43 PM UTC+1, piglet wrote:

On 06/01/2020 14:01, Klaus Kragelund wrote:
Hi

I have a Colpitts osc that is giving me a headache in radiated EMI

If I could pull the frequency at 100Hz so the energy is spread out, it could solve my problem

Sort of like this:

https://www.researchgate.net/publication/251979186_Simulation_and_implementation_of_improved_chaotic_Colpitts_circuit_for_UWB_communications

It looks like they use the inherent properties of the transistor to make a chaotic signal

I am using a standard BC847, so cannot do this

Anybody have an idea how to pull the frequency, cheap?

Sort of like an varicap across the tank caps, but varicaps are not cheap?

Cheers

Klaus


If you can tolerate AM and the colpitts is high enough frequency you can
modulate the oscillator transistor capacitances by injecting some wobble
into it's base. Or instead of a costly varicap across the tank use a
second vanilla BC847 across the tank either varicapping C-B or B-E
junctions or as an old school reactance modulator (should be findable
online).

I like the idea to inject into the base. I guess it should be an ac coupled cap. I have mains input voltage, so I could even feed mains ripple from the DC link capacitor into this point.

Cheers

Klaus

 

[Klaus Kragelund]

On Monday, January 6, 2020 at 11:48:59 PM UTC+1, John S wrote:

On 1/6/2020 12:24 PM, John Larkin wrote:
On Mon, 6 Jan 2020 10:18:57 -0800 (PST), jrwalliker@gmail.com wrote:

On Monday, 6 January 2020 15:56:45 UTC, jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass filtering a
pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being jittered
by the pseudorandom bit stream...

John

It's interesting to consider making truly random bit streams from a
small uP. It needs an external source of entropy.

One idea is to pull down a tri-state pin and let it charge back up
into the same, or another input pin, logic or an ADC input. That
generates a sorta random time delay or number. Stir that into the guts
of a pseudorandom sequence generator or several.


What about taking the audio output of a radio tuned off-station as an
input to a processor for random numbers?

I do not have a radio receiver in this product

 

[LM]

What kind of metal shielding you have around the oscillator and parts
that follow it. It must be leaky if you have problems.
On Mon, 6 Jan 2020 06:01:28 -0800 (PST), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

Hi

I have a Colpitts osc that is giving me a headache in radiated EMI

If I could pull the frequency at 100Hz so the energy is spread out, it could solve my problem

Sort of like this:

https://www.researchgate.net/publication/251979186_Simulation_and_implementation_of_improved_chaotic_Colpitts_circuit_for_UWB_communications

It looks like they use the inherent properties of the transistor to make a chaotic signal

I am using a standard BC847, so cannot do this

Anybody have an idea how to pull the frequency, cheap?

Sort of like an varicap across the tank caps, but varicaps are not cheap?

Cheers

Klaus

 

[Klaus Kragelund]

On Tuesday, January 7, 2020 at 12:29:14 AM UTC+1, LM wrote:

What kind of metal shielding you have around the oscillator and parts
that follow it. It must be leaky if you have problems.

No shielding. It is leaking via a capacitance across a barrier. I have no clear way to reduce that leaking. I need to try other tricks

Cheers

Klaus

 

[John Larkin]

On Mon, 6 Jan 2020 15:10:27 -0800 (PST), Klaus Kragelund
<klauskvik@hotmail.com> wrote:

On Monday, January 6, 2020 at 11:48:59 PM UTC+1, John S wrote:
On 1/6/2020 12:24 PM, John Larkin wrote:
On Mon, 6 Jan 2020 10:18:57 -0800 (PST), jrwalliker@gmail.com wrote:

On Monday, 6 January 2020 15:56:45 UTC, jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass filtering a
pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being jittered
by the pseudorandom bit stream...

John

It's interesting to consider making truly random bit streams from a
small uP. It needs an external source of entropy.

One idea is to pull down a tri-state pin and let it charge back up
into the same, or another input pin, logic or an ADC input. That
generates a sorta random time delay or number. Stir that into the guts
of a pseudorandom sequence generator or several.


What about taking the audio output of a radio tuned off-station as an
input to a processor for random numbers?

I do not have a radio receiver in this product

You don't need anything fancy for spread-spectrum. I've used a sloppy
triangle from a schmitt-gate-RC oscillator. If you have a uP output
pin, lowpass that and square wave drive to make a triangle. Fancy
pseudo-random the pin to make a gaussion spectrum. But a triangle is
fine, to make a rectangular spectrum.

Any diode is a varicap. It could be as simple as a schmitt gate, one
resistor, one cap, one diode. Possibly simpler, depending on your
oscillator circuit.






--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

 

[Steve Wilson]

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

On Mon, 6 Jan 2020 15:10:27 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Monday, January 6, 2020 at 11:48:59 PM UTC+1, John S wrote:
On 1/6/2020 12:24 PM, John Larkin wrote:
On Mon, 6 Jan 2020 10:18:57 -0800 (PST), jrwalliker@gmail.com wrote:

On Monday, 6 January 2020 15:56:45 UTC,
jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass
filtering a pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being
jittered by the pseudorandom bit stream...

John

It's interesting to consider making truly random bit streams from a
small uP. It needs an external source of entropy.

One idea is to pull down a tri-state pin and let it charge back up
into the same, or another input pin, logic or an ADC input. That
generates a sorta random time delay or number. Stir that into the
guts of a pseudorandom sequence generator or several.


What about taking the audio output of a radio tuned off-station as an
input to a processor for random numbers?

I do not have a radio receiver in this product

You don't need anything fancy for spread-spectrum. I've used a sloppy
triangle from a schmitt-gate-RC oscillator. If you have a uP output
pin, lowpass that and square wave drive to make a triangle. Fancy
pseudo-random the pin to make a gaussion spectrum. But a triangle is
fine, to make a rectangular spectrum.

Any diode is a varicap. It could be as simple as a schmitt gate, one
resistor, one cap, one diode. Possibly simpler, depending on your
oscillator circuit.

The name is important. Octpart shows 174 hits for varicap:

https://octopart.com/search?q=varicap&currency=USD&specs=0

and 1,000 hits for varactor:

https://octopart.com/search?q=varactor&currency=USD&specs=0

The price is generally between $0.10 and $1.00 for qty 1.

The capactance range is wider and probably better controlled than with a
random diode.

1N4001 shows typical values:

http://www.vishay.com/docs/88503/1n4001.pdf

1N4148 shows maximum value:

https://www.vishay.com/docs/81857/1n4148.pdf

 

On Tue, 7 Jan 2020 04:43:51 -0000 (UTC), Steve Wilson <no@spam.com>
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

On Mon, 6 Jan 2020 15:10:27 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Monday, January 6, 2020 at 11:48:59 PM UTC+1, John S wrote:
On 1/6/2020 12:24 PM, John Larkin wrote:
On Mon, 6 Jan 2020 10:18:57 -0800 (PST), jrwalliker@gmail.com wrote:

On Monday, 6 January 2020 15:56:45 UTC,
jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass
filtering a pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being
jittered by the pseudorandom bit stream...

John

It's interesting to consider making truly random bit streams from a
small uP. It needs an external source of entropy.

One idea is to pull down a tri-state pin and let it charge back up
into the same, or another input pin, logic or an ADC input. That
generates a sorta random time delay or number. Stir that into the
guts of a pseudorandom sequence generator or several.


What about taking the audio output of a radio tuned off-station as an
input to a processor for random numbers?

I do not have a radio receiver in this product

You don't need anything fancy for spread-spectrum. I've used a sloppy
triangle from a schmitt-gate-RC oscillator. If you have a uP output
pin, lowpass that and square wave drive to make a triangle. Fancy
pseudo-random the pin to make a gaussion spectrum. But a triangle is
fine, to make a rectangular spectrum.

Any diode is a varicap. It could be as simple as a schmitt gate, one
resistor, one cap, one diode. Possibly simpler, depending on your
oscillator circuit.

The name is important. Octpart shows 174 hits for varicap:

https://octopart.com/search?q=varicap&currency=USD&specs=0

and 1,000 hits for varactor:

https://octopart.com/search?q=varactor&currency=USD&specs=0

The price is generally between $0.10 and $1.00 for qty 1.

The capactance range is wider and probably better controlled than with a
random diode.

Then don't use a random diode! I think Klaus is super price sensitive,
so some under-one-cent diode might be appropriate.

We don't know his frequency or the circuit, so we can't recommend
anything.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Steve Wilson]

jlarkin@highlandsniptechnology.com wrote:

On Tue, 7 Jan 2020 04:43:51 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

Any diode is a varicap. It could be as simple as a schmitt gate, one
resistor, one cap, one diode. Possibly simpler, depending on your
oscillator circuit.

The name is important. Octpart shows 174 hits for varicap:

https://octopart.com/search?q=varicap&currency=USD&specs=0

and 1,000 hits for varactor:

https://octopart.com/search?q=varactor&currency=USD&specs=0

The price is generally between $0.10 and $1.00 for qty 1.

The capactance range is wider and probably better controlled than with a
random diode.

Then don't use a random diode! I think Klaus is super price sensitive,
so some under-one-cent diode might be appropriate.

Good luck finding a diode under a cent with controlled capacitance
characteristice that can be used in his circuit.

Perhaps shielding might work better, or adjusting the operating parameters
of the oscillator to reduce EMI.

For examples of properly adjusted Colpitts, see

https://drive.google.com/open?id=1ZsbpkV0aaKS5LURIb1dfu_ndshsSaYtf

Follow the instructions in the Readme.txt file.

 

[Klaus Kragelund]

On Tuesday, January 7, 2020 at 6:11:39 AM UTC+1, jla...@highlandsniptechnology.com wrote:

On Tue, 7 Jan 2020 04:43:51 -0000 (UTC), Steve Wilson <no@spam.com
wrote:

John Larkin <jlarkin@highland_atwork_technology.com> wrote:

On Mon, 6 Jan 2020 15:10:27 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Monday, January 6, 2020 at 11:48:59 PM UTC+1, John S wrote:
On 1/6/2020 12:24 PM, John Larkin wrote:
On Mon, 6 Jan 2020 10:18:57 -0800 (PST), jrwalliker@gmail.com wrote:

On Monday, 6 January 2020 15:56:45 UTC,
jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass
filtering a pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being
jittered by the pseudorandom bit stream...

John

It's interesting to consider making truly random bit streams from a
small uP. It needs an external source of entropy.

One idea is to pull down a tri-state pin and let it charge back up
into the same, or another input pin, logic or an ADC input. That
generates a sorta random time delay or number. Stir that into the
guts of a pseudorandom sequence generator or several.


What about taking the audio output of a radio tuned off-station as an
input to a processor for random numbers?

I do not have a radio receiver in this product

You don't need anything fancy for spread-spectrum. I've used a sloppy
triangle from a schmitt-gate-RC oscillator. If you have a uP output
pin, lowpass that and square wave drive to make a triangle. Fancy
pseudo-random the pin to make a gaussion spectrum. But a triangle is
fine, to make a rectangular spectrum.

Any diode is a varicap. It could be as simple as a schmitt gate, one
resistor, one cap, one diode. Possibly simpler, depending on your
oscillator circuit.

The name is important. Octpart shows 174 hits for varicap:

https://octopart.com/search?q=varicap&currency=USD&specs=0

and 1,000 hits for varactor:

https://octopart.com/search?q=varactor&currency=USD&specs=0

The price is generally between $0.10 and $1.00 for qty 1.

The capactance range is wider and probably better controlled than with a
random diode.

Then don't use a random diode! I think Klaus is super price sensitive,
so some under-one-cent diode might be appropriate.

Yes, as always

We don't know his frequency or the circuit, so we can't recommend
anything.

I wrote that in another post, about 20MHz

Cheers

Klaus

 

[Klaus Kragelund]

On Tuesday, January 7, 2020 at 1:46:24 AM UTC+1, John Larkin wrote:

On Mon, 6 Jan 2020 15:10:27 -0800 (PST), Klaus Kragelund
klauskvik@hotmail.com> wrote:

On Monday, January 6, 2020 at 11:48:59 PM UTC+1, John S wrote:
On 1/6/2020 12:24 PM, John Larkin wrote:
On Mon, 6 Jan 2020 10:18:57 -0800 (PST), jrwalliker@gmail.com wrote:

On Monday, 6 January 2020 15:56:45 UTC, jla...@highlandsniptechnology.com wrote:

Is there a uP port pin available? You can have fun lowpass filtering a
pseudoramdom bit stream.

Especially if the uP is clocked by the oscillator which is being jittered
by the pseudorandom bit stream...

John

It's interesting to consider making truly random bit streams from a
small uP. It needs an external source of entropy.

One idea is to pull down a tri-state pin and let it charge back up
into the same, or another input pin, logic or an ADC input. That
generates a sorta random time delay or number. Stir that into the guts
of a pseudorandom sequence generator or several.


What about taking the audio output of a radio tuned off-station as an
input to a processor for random numbers?

I do not have a radio receiver in this product

You don't need anything fancy for spread-spectrum. I've used a sloppy
triangle from a schmitt-gate-RC oscillator. If you have a uP output
pin, lowpass that and square wave drive to make a triangle. Fancy
pseudo-random the pin to make a gaussion spectrum. But a triangle is
fine, to make a rectangular spectrum.

Any diode is a varicap. It could be as simple as a schmitt gate, one
resistor, one cap, one diode. Possibly simpler, depending on your
oscillator circuit.

Yes, I am working on this. I have a couple of pins free on the micro, so could use these for the function.

About the receiver comment, it's just that another post suggested a radio receiver, and as I wrote I do not have that luxury ;-)

Cheers

Klaus