EMRFD Message Archive 4306
Message Date From Subject 4306 2010-02-20 16:00:11 hariz yacine LC circuit
[Non-text portions of this message have been removed]4309 2010-02-20 18:20:24 pchamilt1126@aol.... Re: LC circuit
Analogy is slipperier than logic but here goes:
In electrical engineering school one is taught parallel LC oscillators or "tanks" in the classic manner via math and theory. You can get that from any introductory text on electrical engineering.
The metaphor that helps me visualize what is going on is that of a child being pushed on a swing. The swing has a natural frequency that is a function of the length of the chain or rope and the gravitational constant. At the top of the swinging arc all of the energy of the pendulum is stored as potential energy based on the mass of the pendulum bob, in this case the child. At the bottom of the arc, all of the energy of the pendulum is stored as kinetic energy, based on the velocity of the pendulum bob, again in this case, the child. The person pushing the swing adds energy in phase with the natural frequency and in the same direction. This either increases the height of swinging or just replaces frictional losses. The pendulum or child on a swing is a natural harmonic resonator.
An LC oscillator works in a similar manner. The inductor stores energy as magnetic field due to the sinusoidal current flowing through it. When the current through the inductor is at a maximum, the stored energy of the magnetic field is also at a maximum. When the voltage across the capacitor is at a maximum it's stored energy is also at a maximum. These two events are at different times, out of phase with each other. This is just like the time difference between the top of the swing's arc and the bottom. The inductor and capacitor trade stored energy back and forth at a frequency defined by:
(omega)^2 = 1/(LC)
where omega =2*pi*F, L is the inductance in Henrys, C is the capacitance in Farads, F is the resonant frequency in Hertz and omega=2(pi)F. (omega)^2 means omega squared.
I hope this helps you.
Regards
Paul Hamilton, KE7UAE
-----Original Message-----
4310 2010-02-20 18:54:45 Stephen Wandling Re: LC circuit
Why do some tank circuits have DC current flowing through them, and some
use a capacitor to keep the DC current from flowing?
72
Stephen
VE7NSD
pchamilt1126@aol.com wrote:
> Hariz,
>
> Analogy is slipperier than logic but here goes:
>
> In electrical engineering school one is taught parallel LC oscillators or "tanks" in the classic manner via math and theory. You can get that from any introductory text on electrical engineering.
>
> The metaphor that helps me visualize what is going on is that of a child being pushed on a swing. The swing has a natural frequency that is a function of the length of the chain or rope and the gravitational constant. At the top of the swinging arc all of the energy of the pendulum is stored as potential energy based on the mass of the pendulum bob, in this case the child. At the bottom of the arc, all of the energy of the pendulum is stored as kinetic energy, based on the velocity of the pendulum bob, again in this case, the child. The person pushing the swing adds energy in phase with the natural frequency and in the same direction. This either increases the height of swinging or just replaces frictional losses. The pendulum or child on a swing is a natural harmonic resonator.
>
>
> An LC oscillator works in a similar manner. The inductor stores energy as magnetic field due to the sinusoidal current flowing through it. When the current through the inductor is at a maximum, the stored energy of the magnetic field is also at a maximum. When the voltage across the capacitor is at a maximum it's stored energy is also at a maximum. These two events are at different times, out of phase with each other. This is just like the time difference between the top of the swing's arc and the bottom. The inductor and capacitor trade stored energy back and forth at a frequency defined by:
>
> (omega)^2 = 1/(LC)
>
> where omega =2*pi*F, L is the inductance in Henrys, C is the capacitance in Farads, F is the resonant frequency in Hertz and omega=2(pi)F. (omega)^2 means omega squared.
>
> I hope this helps you.
>
> Regards
>
> Paul Hamilton, KE7UAE
>
>
>
>
>
> -----Original Message-----
>4311 2010-02-21 02:03:57 harizyacine Re: LC circuit 2
it's usful reply but I have some Comments,if we take tank circuit alone and feed by dc curent will does that event just one time how it works in the circuit I mean by all my question that some designer make LC circuit like an reciever and other like oscillator works like reciever also remember the coil pass dc curent through it and it's sensitive to wireless field.
here an exemple not oscillator
http://www.vk2zay.net/article/186
and here regenerative detector (oscillator and reciever)
http://www.vk2zay.net/article/156
thanks4312 2010-02-21 15:12:37 tim Re: LC circuit 2
v=L (di/dt)
You get a time-varying voltage v define by the inductance times the rate of
change in current over time.
A dc current through an inductor doesn't vary over time so it generates no
voltage (other than the resistance drop through the wire of the inductor).
So it would seem that it doesn't really matter if you run DC through tank
circuits inductor or not, it shouldn't change the resonant frequency of the
tank circuit at all.
tim ab0wr
On Sunday 21 February 2010 04:03:51 am harizyacine wrote:
> Hi,thank Stephen
> it's usful reply but I have some Comments,if we take tank circuit alone and
> feed by dc curent will does that event just one time how it works in the
> circuit I mean by all my question that some designer make LC circuit like
> an reciever and other like oscillator works like reciever also remember
> the coil pass dc curent through it and it's sensitive to wireless field.
> here an exemple not oscillator
> http://www.vk2zay.net/article/186
> and here regenerative detector (oscillator and reciever)
> http://www.vk2zay.net/article/156
> thanks
>4313 2010-02-21 15:27:34 hariz Re: LC circuit 2
I will try to simplify my subject,what I have talked about Briefly is :
may you know that some oscillator or most we can make it like recievers for Certain Frequency.
what I have observed in some receivers design that there is a dc current pass through tank circuit,how it can detects a wave with dc current?
here an example of Transceiver look to the tank circuit.
http://www.vk2zay.net/article/156
in other side if I joined a colector of transistor with its base by LC and I considered it like a receiver is it oscillates ?
hope that I explained my Idea for you
regard4314 2010-02-21 15:42:13 hariz Re: LC circuit 2
so,it will be sensetive Although dc current pass through it4315 2010-02-21 15:55:33 Brent G DeWitt Re: LC circuit 2
If the inductor has an air core, the DC current won't matter until the wire
melts. With ferrite and powdered iron cores, the situation is more complex,
and you will need core data and some calculations.
Brent
4316 2010-02-21 16:18:46 Stephen Wandling Re: LC circuit 2
that scary place, my brain, I thought I saw something about DC current
affecting Q? Is there any issue with getting an oscillator, with DC in
it's tank circuit, to start? From your post, I suspect the answer to
both questions is No.
72
Stephen
tim wrote:
>
>
> So it would seem that it doesn't really matter if you run DC through tank
> circuits inductor or not, it shouldn't change the resonant frequency of the
> tank circuit at all.
>
> tim ab0wr
>4328 2010-02-22 11:16:57 hariz Clarification
my next question is Abbreviate for what we have all talked about
is no dc current makes tank circuit Generates a constant magnetic field and Loses Its function ? for oscillator or reciever
thanks4329 2010-02-22 11:56:01 Lasse Re: LC circuit and current
be altered by having a current flowing...
Don't thik it was a hit though, but there might be one in my junkbox
somewhere!
/Lasse4330 2010-02-22 12:15:46 Stephen Wandling Re: Clarification
If I understand your question, you are asking: if there is no DC current
in a tank circuit, does it generate a constant magnetic field, and does
it then lose its function for being an oscillator or receiver? My short
answers would be No, and No.
My understanding, based on what Tim wrote (sorry about calling you Ted)
is this: Regardless of whether there is a DC current in a tank circuit
or not, the changes in the magnetic field will be determined by the
other components connected to the tank circuit. The only effect a DC
current has in a tank circuit, that is not connected to anything else,
is to create a very short magnetic field when you connect the DC current
and when you disconnect it. While the DC current is connected there is
no magnetic field that is created by the DC current.
And, regardless of whether there is a DC current in a tank circuit or
not, it can still function in a receiver or an oscillator.
For further clarification, it is my understanding that the term "tank
circuit" typically refers to a capacitor in parallel with an inductor.
It seems to me that neither of the circuits you posted from the Alan
Yates site contain simple "tank circuits".
Let me know if this helps.
72
Stephen
VE7NSD
hariz wrote:
> thank stephen
> my next question is Abbreviate for what we have all talked about
> is no dc current makes tank circuit Generates a constant magnetic field and Loses Its function ? for oscillator or reciever
> thanks
>
>
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>4331 2010-02-22 13:34:31 k5nwa Re: Clarification
>A steady magnetic field will change the inductance of the coil by
>
>Hariz,
>
>If I understand your question, you are asking: if there is no DC current
>in a tank circuit, does it generate a constant magnetic field, and does
>it then lose its function for being an oscillator or receiver? My short
>answers would be No, and No.
>
>My understanding, based on what Tim wrote (sorry about calling you Ted)
>is this: Regardless of whether there is a DC current in a tank circuit
>or not, the changes in the magnetic field will be determined by the
>other components connected to the tank circuit. The only effect a DC
>current has in a tank circuit, that is not connected to anything else,
>is to create a very short magnetic field when you connect the DC current
>and when you disconnect it. While the DC current is connected there is
>no magnetic field that is created by the DC current.
>
>And, regardless of whether there is a DC current in a tank circuit or
>not, it can still function in a receiver or an oscillator.
>
>For further clarification, it is my understanding that the term "tank
>circuit" typically refers to a capacitor in parallel with an inductor.
>It seems to me that neither of the circuits you posted from the Alan
>Yates site contain simple "tank circuits".
>
>Let me know if this helps.
>
>72
>Stephen
>VE7NSD
having operate in a different part of the BH curve. The effect will
be to shift the resonant frequency of the tuned circuit, there are
limits on the amount of the steady field otherwise you will shift the
operating point enough to get into the saturation part of the curve.
It's an expensive way to shift the resonant because of the required
current for the coil.
Cecil
K5NWA
www.softrockradio.org www.qrpradio.com
"Blessed are the cracked, for they shall let in the light."4332 2010-02-22 16:02:17 hariz Re: Clarification 4333 2010-02-22 16:10:56 Stephen Wandling Re: Clarification
Are you speaking of an external magnetic field that's applied to a tank
circuit?
Or maybe you are replying to Lasse's post about the 'special inductor'?
Thanks
72
Stephen
VE7NSD
k5nwa wrote:
> At 02:14 PM 2/22/2010, you wrote:
> A steady magnetic field will change the inductance of the coil by
> having operate in a different part of the BH curve. The effect will
> be to shift the resonant frequency of the tuned circuit, there are
> limits on the amount of the steady field otherwise you will shift the
> operating point enough to get into the saturation part of the curve.
> It's an expensive way to shift the resonant because of the required
> current for the coil.
>
>
>
> Cecil
> K5NWA
> www.softrockradio.org www.qrpradio.com
>
> "Blessed are the cracked, for they shall let in the light."
>
>4334 2010-02-22 16:12:29 Stephen Wandling Re: Clarification
hariz wrote:
> thank stefen yes that helps. So,I understand that a dc current going through the LC circuit will not effect its work whether in oscillator or reciver?
>
>
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>4336 2010-02-22 18:26:17 k5nwa Re: Clarification
At 06:10 PM 2/22/2010, you wrote:
>Cecil
>
>Cecil,
>
>Are you speaking of an external magnetic field that's applied to a tank
>circuit?
>
>Or maybe you are replying to Lasse's post about the 'special inductor'?
>
>Thanks
>
>72
>Stephen
>VE7NSD
>
>k5nwa wrote:
> > At 02:14 PM 2/22/2010, you wrote:
>
> > A steady magnetic field will change the inductance of the coil by
> > having operate in a different part of the BH curve. The effect will
> > be to shift the resonant frequency of the tuned circuit, there are
> > limits on the amount of the steady field otherwise you will shift the
> > operating point enough to get into the saturation part of the curve.
> > It's an expensive way to shift the resonant because of the required
> > current for the coil.
> >
> >
> >
> > Cecil
> > K5NWA
> > www.softrockradio.org www.qrpradio.com
> >
> > "Blessed are the cracked, for they shall let in the light."
> >
> >
>
k5nwa
< www.softrockradio.org > < www.qrpradio.com >
< http://parts.softrockradio.org/ >
Never take life seriously. Nobody gets out alive anyway.4337 2010-02-22 18:35:43 Stephen Wandling Re: Clarification
the effect of DC current on a tank circuit.
k5nwa wrote:
> Any field that gets into the core will affect it if it's strong enough.
>
> At 06:10 PM 2/22/2010, you wrote:
>
>> Cecil,
>>
>> Are you speaking of an external magnetic field that's applied to a tank
>> circuit?
>>
>> Or maybe you are replying to Lasse's post about the 'special inductor'?
>>
>> Thanks
>>
>> 72
>> Stephen
>> VE7NSD
>>
>> k5nwa wrote:
>>
>>> At 02:14 PM 2/22/2010, you wrote:
>>>
>>
>>
>>> A steady magnetic field will change the inductance of the coil by
>>> having operate in a different part of the BH curve. The effect will
>>> be to shift the resonant frequency of the tuned circuit, there are
>>> limits on the amount of the steady field otherwise you will shift the
>>> operating point enough to get into the saturation part of the curve.
>>> It's an expensive way to shift the resonant because of the required
>>> current for the coil.
>>>
>>>
>>>
>>> Cecil
>>> K5NWA
>>> www.softrockradio.org www.qrpradio.com
>>>
>>> "Blessed are the cracked, for they shall let in the light."
>>>
>>>
>>>
>
> Cecil
> k5nwa
> < www.softrockradio.org > < www.qrpradio.com >
> < http://parts.softrockradio.org/ >
>
> Never take life seriously. Nobody gets out alive anyway.
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>
>
>
>
>4338 2010-02-23 01:25:50 hariz Re: Clarification
thanks4340 2010-02-23 06:52:12 Chris Trask Re: Clarification
> yes, I am speaking about an external magnetic field that's applied
> to a tank in radio projcts but with a dc current pass through tank
> circuit that what I found it in some design
> thanks
>
A strong external magnetic field can also affect the core permeability. There are devices known as transductors, a form of saturable reactor, that provice remote tuning by way of producing a strong magnetic bias field in the core that alters the permeability. You don't see these very often as varactors are much less expensive, however they are very useful in remotely tuned antenna matching networks where power levels preclude the use of varactors.
Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/4341 2010-02-23 07:38:10 Dave Re: Clarification 4342 2010-02-23 07:54:45 w0ep Re: Clarification
> > A strong external magnetic field can also affect the core
> permeability. There are devices known as transductors, a form of
> saturable reactor, that provice remote tuning by way of producing a
> strong magnetic bias field in the core that alters the permeability.
> You don't see these very often as varactors are much less expensive,
> however they are very useful in remotely tuned antenna matching
> networks where power levels preclude the use of varactors.
>
> The effect can, and has, been used for tuning the resonant frequency of an
> LC circuit:
>
> http://www.hanssummers.com/radio/huffpuff/fast/index.htm
> <http://www.hanssummers.com/radio/huffpuff/fast/index.htm>
>
http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf4343 2010-02-23 07:56:34 Chris Trask Re: Clarification
> > A strong external magnetic field can also affect the core
> > permeability. There are devices known as transductors, a form
> > of saturable reactor, that provice remote tuning by way of
> > producing a strong magnetic bias field in the core that alters
> > the permeability. You don't see these very often as varactors
> > are much less expensive, however they are very useful in
> > remotely tuned antenna matching networks where power levels
> > preclude the use of varactors.
>
> The effect can, and has, been used for tuning the resonant frequency of an
> LC circuit:
>
> http://www.hanssummers.com/radio/huffpuff/fast/index.htm
>
Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/4344 2010-02-23 08:02:43 Chris Trask Re: Clarification
> >
> > >
> > > A strong external magnetic field can also affect the core
> > > permeability. There are devices known as transductors, a form of
> > > saturable reactor, that provice remote tuning by way of producing a
> > > strong magnetic bias field in the core that alters the permeability.
> > > You don't see these very often as varactors are much less expensive,
> > > however they are very useful in remotely tuned antenna matching
> > > networks where power levels preclude the use of varactors.
> >
> > The effect can, and has, been used for tuning the resonant frequency
> > of an LC circuit:
> >
> > http://www.hanssummers.com/radio/huffpuff/fast/index.htm
> > <http://www.hanssummers.com/radio/huffpuff/fast/index.htm>
> >
>
> And a wide-ranging VCO
> http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf
>
Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/4345 2010-02-23 08:04:28 Matt Palmer Re: Clarification
Matt
W8ESE
sent from my VIC-20
4346 2010-02-23 08:18:40 Russ Hines Re: Clarification
current changing the permeability?
Otherwise, it would seem there should be some AC component on the DC for
the effect you mention to occur. Since we're talking about tank
circuits, it seems circulating RF currents would be the overwhelming
source for this, as to make any DC current effect negligible.
I just don't have enough experience or knowledge of transductors and
magnetic amplifiers, so I submit to your analysis.
Thanks,
73,
Russ
WB8ZCC
Chris Trask wrote:
>[Non-text portions of this message have been removed]
>
> >
> > yes, I am speaking about an external magnetic field that's applied
> > to a tank in radio projcts but with a dc current pass through tank
> > circuit that what I found it in some design
> > thanks
> >
>
> As k5nwa had stated earlier, a DC current passing through the inductor
> can affect the tuning of the tank circuit, provided that the inductor
> has a core of magnetic material and the DC current combined with the
> number of turns is sufficient to affect the permeability of the core.
> This effect is more noticable with higher permeability ferrite
> materials such as Fair-Rite mixes 43, 73, and 77 and Ferroxcube 3F3.
> You will not see this effect in powdered iron materials as the initial
> permeability is much too low.
>
> A strong external magnetic field can also affect the core
> permeability. There are devices known as transductors, a form of
> saturable reactor, that provice remote tuning by way of producing a
> strong magnetic bias field in the core that alters the permeability.
> You don't see these very often as varactors are much less expensive,
> however they are very useful in remotely tuned antenna matching
> networks where power levels preclude the use of varactors.
>
> Chris Trask
> N7ZWY / WDX3HLB
> Senior Member IEEE
> http://www.home.earthlink.net/~christrask/
> <http://www.home.earthlink.net/%7Echristrask/>
>
>
>
>
> __________ NOD32 4888 (20100222) Information __________
>
> This message was checked by NOD32 antivirus system.
> http://www.eset.com
4347 2010-02-23 08:28:44 w0ep Re: Clarification
> > > http://www.hanssummers.com/radio/huffpuff/fast/index.htm
> <http://www.hanssummers.com/radio/huffpuff/fast/index.htm>
> > > <http://www.hanssummers.com/radio/huffpuff/fast/index.htm
> <http://www.hanssummers.com/radio/huffpuff/fast/index.htm>>
> > >
> >
> > And a wide-ranging VCO
> > http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf
> <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf>
> >
>
> Nice. I wasn't aware of that one.
>
a follower PLL for a DDS.
I found this article and it lead me to at least try to figure out what
the thing was about. I was reading
in Terman a bit to try to see if he talks about low-power saturable
inductors but could not find anything obvious. Everything seems to
be geared toward higher saturation not low saturation.
I did find a powerpoint presentation online that talked about
some materials having a nice gradual saturation curve. But I was
soon in over my head with the magnetic flux terminology.
Whether or not following a DDS would actually be useful is not something
I am qualified to answer.4348 2010-02-23 08:36:09 sm5glc Current Controlled Inductors
From the simplified drawings it appears to be an inductor with a additional winding which is used to inject a control current (0 to 60 mA)
The inductor range goes from 20 milliH down to 0.5 microH and the adjustment range appears to 4:1 or better. High inductance inductors seems to be more "controllable" and have >10:1 range i.e. 22 microH to 5 milliH with currents from 0 to 60 mA.
Control winding inductance goes from 75 up to 450 milliH
Pity they do not list any Q values... nor any linearity diagrams.
Í just found two very very old boxes containing one M-P1 and one M-P5.
The latter is 0.5 to 0.125 microH but I lack data on the M-P1. See if I can produce some real measured Q and inductance vs. current on these.
BTW boxes indicated that VariL was located in Stamford Conn, but catalogue says Denver Co. Anyone know when they did move?4349 2010-02-23 08:52:48 Leon Heller Re: Current Controlled Inductors 4350 2010-02-23 08:53:49 sm5glc Re: Current Controlled Inductors
Joseph Kiser founded Vari-L in Stamford, Conn., in 1953; its first contract was to supply electrical inductors to the Navy. He moved it to Colorado in 1969. In 1992, the company started manufacturing components for the growing wireless industry. Vari-L went public in 1994.
After 50 years it went belly-up :(
http://denver.bizjournals.com/denver/stories/2004/04/05/story5.html4351 2010-02-23 09:00:40 w0ep Re: Clarification
> > > And a wide-ranging VCO
> > > http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf
> <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf>
> > <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf
> <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf>>
> > >
>
material
inside a magnetic field changes inductance with the strength of the magnetic
field. As the magnetic field increases inductance goes up until
a saturation point and then continued increase in magnetic field makes
inductance go down. Different core materials have different
inductance/saturation curves.
Some core materials have a post-saturation inductance curve
that goes down gradually as the saturating magnetic field is increased,
some drop faster. I think his paper implies that he is using the
post-saturation part of the curve for his coil.
This guy has a small electro magnet operating on variable DC current
in proximity to his VCO coil which changes the inductance of the VCO coil.
He has a circuit which automatically regulates the current through the
electromagnet. The tuning is all via varicaps but he achieves
a wide frequency range.
As the frequency of the VCO goes up, the reactance of the VCO coil
goes up. His circuit attempts to maintain a constant reactance in the coil
by varying the saturating magnetic field, so varicap changes no longer have
a multiplier effect.
It seems pretty slick to me except for a couple of things: 1) changes in
mechanical construction would change the tuning, so would have to be very
rigid and 2) how much current is required in the electromagnet?4352 2010-02-23 09:29:04 Russ Hines Re: Clarification
tank circuit, isn't it?
Just asking...
73,
Russ
WB8ZCC
w0ep wrote:
>[Non-text portions of this message have been removed]
>
>
> >
> > > > And a wide-ranging VCO
> > > > http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf
> <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf>
> > <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf
> <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf>>
> > > <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf
> <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf>
> > <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf
> <http://www.wenzel.com/pdffiles1/pdfs/crvco.pdf>>>
> > > >
> >
> If I understand this right, an inductor that is operating using core
> material
> inside a magnetic field changes inductance with the strength of the
> magnetic
> field. As the magnetic field increases inductance goes up until
> a saturation point and then continued increase in magnetic field makes
> inductance go down. Different core materials have different
> inductance/saturation curves.
> Some core materials have a post-saturation inductance curve
> that goes down gradually as the saturating magnetic field is increased,
> some drop faster. I think his paper implies that he is using the
> post-saturation part of the curve for his coil.
>
> This guy has a small electro magnet operating on variable DC current
> in proximity to his VCO coil which changes the inductance of the VCO coil.
> He has a circuit which automatically regulates the current through the
> electromagnet. The tuning is all via varicaps but he achieves
> a wide frequency range.
>
> As the frequency of the VCO goes up, the reactance of the VCO coil
> goes up. His circuit attempts to maintain a constant reactance in the coil
> by varying the saturating magnetic field, so varicap changes no longer
> have
> a multiplier effect.
>
> It seems pretty slick to me except for a couple of things: 1) changes in
> mechanical construction would change the tuning, so would have to be very
> rigid and 2) how much current is required in the electromagnet?
>
>
>
>
> __________ NOD32 4888 (20100222) Information __________
>
> This message was checked by NOD32 antivirus system.
> http://www.eset.com
4353 2010-02-23 09:29:33 w0ep Re: Clarification
>I shouldn't have put this last part in. I really can't say I know enough
>
> It seems pretty slick to me except for a couple of things: 1) changes in
> mechanical construction would change the tuning, so would have to be very
> rigid and 2) how much current is required in the electromagnet?
>
to make an intelligent assessment.4354 2010-02-23 09:29:58 Nick Kennedy Re: Clarification
was controlled by DC current in the tank coil. It was based on the
referenced EDN article.
http://pages.suddenlink.net/wa5bdu/current_controlled_oscillator.htm
73-
Nick, WA5BDU
[Non-text portions of this message have been removed]4355 2010-02-23 09:41:48 w0ep Re: Clarification
>The DC current changes the encompassing
>
> While interesting, all this is kind of tangent to DC current through a
> tank circuit, isn't it?
>
> Just asking...
>
magnetic field which would change the part of the
inductance curve your coil was working on.
If capacitance were held fixed, change in
DC current would have some change in frequency of the tank
depending on the core material.
Or so it would seem to me.4356 2010-02-23 10:30:44 Chris Trask Re: Clarification
> I had been searching for a VCO because I was thinking about
> a follower PLL for a DDS.
>
> I found this article and it lead me to at least try to figure out what
> the thing was about. I was reading
> in Terman a bit to try to see if he talks about low-power saturable
> inductors but could not find anything obvious. Everything seems to
> be geared toward higher saturation not low saturation.
> I did find a powerpoint presentation online that talked about
> some materials having a nice gradual saturation curve. But I was
> soon in over my head with the magnetic flux terminology.
>
> Whether or not following a DDS would actually be useful is not something
> I am qualified to answer.
>
http://www.home.earthlink.net/~christrask/trnsdctr.html
Everything I've been able to find on the subject is listed there.
Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/4357 2010-02-23 10:32:39 Chris Trask Re: Clarification
> Hmm... Chris, are you talking about heating of the core from the DC
> current changing the permeability?
>
magnetic bias flux in the core. That changes the permeability, and there's
a matter of whether the bias flux is orthogonal or parellel with the signal
flux. When it's parellel, the effect is much sharper as you are forcing the
signal flux up against the saturation of the core, which produces all sorts
of distortion. This is how electric arc welders perform frequency
multiplication so as to get a better bead on the welding.
When the bias flux is orthogonal to the signal flux, the signal flux
remains in the centre of the B-H curve. This takes more bias flux than the
parallel bias to change the permeability, but at the same time you will
isolate the signal and control windings as well as avoid the distortion due
to core saturation.
>No, there is no AC component on the bias current unles you intend to
> Otherwise, it would seem there should be some AC component on the DC for
> the effect you mention to occur.
>
make what's known as a magnetic modulator. Those are interesting little
devices that have passed into history a very long time ago.
Chris Trask
N7ZWY / WDX3HLB
Senior Member IEEE
http://www.home.earthlink.net/~christrask/4358 2010-02-23 10:38:42 Russ Hines Re: Clarification
no longer DC, is it? Like switching transients, I can see how this can
effect the electromagnetic field.
So, even micro-small current changes in the DC supply could effect the
magnetic field induced, since it's not strictly-speaking a pure DC
current anymore. Yes? No?
This discussion is very interesting, keep it coming. I'm going back to
my battery, a nail and coil of wire now... ;-)
73,
Russ
WB8ZCC
w0ep wrote:
>[Non-text portions of this message have been removed]
>
> Russ Hines wrote:
> >
> >
> > While interesting, all this is kind of tangent to DC current through a
> > tank circuit, isn't it?
> >
> > Just asking...
> >
> The DC current changes the encompassing
> magnetic field which would change the part of the
> inductance curve your coil was working on.
>
> If capacitance were held fixed, change in
> DC current would have some change in frequency of the tank
> depending on the core material.
>
> Or so it would seem to me.
>
>
>
>
> __________ NOD32 4888 (20100222) Information __________
>
> This message was checked by NOD32 antivirus system.
> http://www.eset.com
4359 2010-02-23 11:09:42 Roelof Bakker Re: Clarification
I can't find my notes, but if I remember correct, this technique was used
in a Marconi sweepgenerator.
I have build a similar oscillator and the V/F curve was amazingly linear.
On an other note, the inductance of a toroid can be sensitive to the
applied AC voltage as well.
In an attemp to minimise the size of a LC audio filter, 200 windings were
squeezed on a FT-37-43 core.
Not the most suitable core material, but it was done, just out of
curiosity.
The core had an inductance of 19 mH.
A parallel tuned circuit was made consisting of this coil and a 1 uF
capacitor.
An audio generator was coupled to this tuned circuit via a 10 nF capacitor.
The voltage over the tuned circuit was measured with a scope and a 10M
probe
This was found:
1 mV-pp, F = 1214 Hz and L = 17.2 mH.
5 mV-pp, F = 1162 Hz and l = 18.8 mH.
10 mV-pp, F = 1134 Hz and l = 19.7 mH.
15 mV-pp, F = 1103 Hz and l = 20.8 mH.
20 mV-pp, F = 1073 Hz and l = 22.0 mH.
25 mV-pp, F = 1064 Hz and l = 22.4 mH.
30 mV-pp, F = 1026 Hz and l = 24.1 mH.
A similar test carried out with a TOKO series 10RB 18 mH coil, did reveal
no change at all in inductance between 1 mV-pp and 80 mV-pp.
I build a LC audio filter with home made 100 mH coils wound on 9 mm / 3E2
/ 5000 u core.
In a receiver it showed that at S-1 the filter centre frequency was 590 Hz.
At S-9 + 30 dB it had dropped to 482 Hz!
This happened in October 1995!
73,
Roelof Bakker, pa0rdt4361 2010-02-23 12:58:10 w0ep Re: Clarification
> Some core materials have a post-saturation inductance curve
> that goes down gradually as the saturating magnetic field is increased,
> some drop faster. I think his paper implies that he is using the
> post-saturation part of the curve for his coil.
>
Back to the books on that part.4362 2010-02-23 15:39:16 joop_l Re: Current Controlled Inductors
> technique.
>
> Leon
> --
> Leon Heller
> G1HSM
>
Joop4363 2010-02-23 15:49:19 joop_l Re: Current Controlled Inductors
>
> Joop
>
http://www.uploadarchief.net/files/download/tf1066b.png
The 1066 needs some repair though. But I never seem to get around to do it.
Joop4364 2010-02-23 15:52:53 tim Re: Clarification
permeability of the core it will not affect how the coil operates in a tank
circuit of a receiver or oscillator. Any adjustable inductor, even a simple
one with a screwdriver adjustment for the core depth in the coil, will need to
be set to the correct operating frequency. The same with a core that has a
permeability that is affected by dc current through the coil.
But this won't change how it operates in the circuit.
v = L (di/dt) still applies.
tim ab0wr
On Tuesday 23 February 2010 08:41:24 am Chris Trask wrote:
> > yes, I am speaking about an external magnetic field that's applied
> > to a tank in radio projcts but with a dc current pass through tank
> > circuit that what I found it in some design
> > thanks
>
> As k5nwa had stated earlier, a DC current passing through the inductor
> can affect the tuning of the tank circuit, provided that the inductor has
> a core of magnetic material and the DC current combined with the number of
> turns is sufficient to affect the permeability of the core. This effect
> is more noticable with higher permeability ferrite materials such as
> Fair-Rite mixes 43, 73, and 77 and Ferroxcube 3F3. You will not see this
> effect in powdered iron materials as the initial permeability is much too
> low.
>
> A strong external magnetic field can also affect the core
> permeability. There are devices known as transductors, a form of
> saturable reactor, that provice remote tuning by way of producing a strong
> magnetic bias field in the core that alters the permeability. You don't
> see these very often as varactors are much less expensive, however they
> are very useful in remotely tuned antenna matching networks where power
> levels preclude the use of varactors.
>
>
> Chris Trask
> N7ZWY / WDX3HLB
> Senior Member IEEE
> http://www.home.earthlink.net/~christrask/
>4367 2010-02-23 18:14:31 Brent G DeWitt Re: Clarification
I'm not clear about what you are saying here. It seems to imply that
inductance is independent of the permeability of the core. Is that what you
meant to say?
Brent
> -----Original Message-----
>4369 2010-02-24 03:51:54 hariz Re: Clarification
thanks4373 2010-02-24 17:32:50 Justin Re: Current Controlled Inductors 4378 2010-02-25 15:32:31 tim Re: Clarification
it could work in an oscillator or receiver.
The DC current doesn't affect how an inductor works in a tank circuit., all it
can do is determine what frequency the tank circuit is resonant at (plus
perhaps some impact on Q if the core is saturated).
This is no different than having a tuned inductor using a core that is screwed
into and out of the inductor. It still works as an inductor in the circuit no
matter how far in or out the core is screwed. The only thing you change is the
resonant frequency of the tank circuit.
v = L(di/dt) still applies.
tim ab0wr
On Tuesday 23 February 2010 08:14:21 pm Brent G DeWitt wrote:
> Hi Tim,
>
> I'm not clear about what you are saying here. It seems to imply that
> inductance is independent of the permeability of the core. Is that what
> you meant to say?
>
> Brent
>
> > -----Original Message-----
> >4379 2010-02-26 04:50:06 davidpnewkirk Re: Current Controlled Inductors