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Trouble with some devices
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Hey guys,
I need some help to simulate my circuit correctly. I want to simulate a UHF-transmitter and I have problems with three devices in my curcuit. Here you can see the circuit diagram: Now the three devices which exasperate me. 1. BB105: I did not find any model for this device. I'm not sure if it's manufacturing stoped. Can someone help me with this? A alternative model or sth. 2. ECM: Like other microphones I used a voltage source in my simulation. Now I'm not sure how to connect it with my curcuit? 3. Silver wire: Can I leave it for a simulation because of the same conductance as a copper wire? Have a nice day, CV |
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John Woodgate
In message <kt5gi5+d3ua@...>, dated Mon, 29 Jul 2013, christianvierck <christianvierck@...> writes:
I need some help to simulate my circuit correctly.I'm not sure we should help you with an illegal transmitter, especially as it can be used to invade privacy. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Why is the stapler always empty just when you want it? John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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Hello Christian,
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When I assume C1=18pF and C30=2pF, a reasonable diode model could be as shown below. .model BB105 D(Is=.1p Rs=1 Bv=35 Ibv=10u Cjo=35p Vj=.75 M=.8) Use Cjo and M to adjust the capacitance. The ECM is a V-source with 1kOhm or 2kOhm output resistance. I think using silver wire or copper wire doesn't matter. You can try to calculate the resistance taking skin effect into account. Be aware that all the components have inductance of 0.5nH to 1nH per mm of wire length. Best regards, Helmut --- In LTspice@..., "christianvierck" <christianvierck@...> wrote:
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Hello CV,
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Original reference uses BFR92 which is plenty good enough for this gadget. Per result of 45 sec search, look in Philips catalogs: (copy entire line sans line breaks) Regarding silver: they likely mean silvered copper to reduce skin effect losses (improve conductance of the wire surface layer, a common treatment of high-power transmitter hardware). Regarding microphone: search for electret microphone. You will see it is a capacitor driving a JFET. ME --- In LTspice@..., "christianvierck" <christianvierck@...> wrote:
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Thank you.
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The model is a good approach for the original device. As I mentioned before, I used a V-source as the ECM and connected the output with the negative cable. I also think that silver wire and copper wire are equal. Now I simulated it(AC) and my frequency at the antenna is a good deal bigger than 900MHz. Probably I made a mistake calculating the inductances of the coil. I will repeat it now. --- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
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Hello Christian,
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You forgot the many x*nH inductance of every component-pin. Best regards, Helmut --- In LTspice@..., "christianvierck" <christianvierck@...> wrote:
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Thank you.
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I used the BFR92 as the BFR92 already. My problem is the BB105 which is not available anymore. The point with the silvered copper seems reasonable. I searched the ECM in english and the third contact makes sense. I searched german webpages before and nothing made sense before. --- In LTspice@..., "miller_effect" <miller_effect@...> wrote:
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I think the frequency is determined by the first stage, with the BB105 and
the 25 mm long wire. The coil L is in the second stage which is an RF amplifier and shouldn't change the frequency (or am I mistaken?). The silver or silvered wire is puzzling. I guess the precise 25 mm length is to make an inductor, and the designer must have thought that it needs very low RF (skin effect) resistance, to get large Q. You would not see that effect unless you include skin effect resistance in your simulation. Andy |
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John Woodgate
In message <kt5rjr+q9qr@...>, dated Mon, 29 Jul 2013, Helmut <helmutsennewald@...> writes:
Be aware that all the components have inductance of 0.5nH to 1nH per mm of wire length.Specifically, that silver wire is an *inductor* and needs to be modelled as such. You can find formulas for the inductance of a wire of specified dimensions on the Internet. -- OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk Why is the stapler always empty just when you want it? John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK |
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@Helmut: I'm not sure how to allocate the inductions to the seperate pins. But I will find out how to manage it.
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@andy:If I change the details on the bb105 diode it does not change the frequency at the antenna. I have splitted the coil into two parts and calculated the induction of both parts separate. When I increase the induction of the coil with two rounds the frequeny decreases. I will test the silver wire as a inductor now. Thank you. --- In LTspice@..., Andy <Andrew.Ingraham@...> wrote:
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Thank you for the advice. I will try this first and find out, how to manage the seperate inductions afterwards.
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--- In LTspice@..., John Woodgate <jmw@...> wrote:
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Hello,
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Every component has a two or more leads. Even if you make it as short as possible, you will always have more than 1nH on every lead. Also one shouldn't forget the capacitance of every device to the ground plane if there is one. Best regards, Helmut --- In LTspice@..., "christianvierck" <christianvierck@...> wrote:
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Or you can model it as a length of transmission line. Below a quarter-wavelength long, it will behave as an inductance, exactly like the real wire does. The thing I don't see specified on the schematic, is the proximity between the wire and the ground plane. The amount of inductance depends not on its length but on the loop area enclosed by the wire and its return path (ground plane), so you would get totally different results for a PCB trace as opposed to a wire suspended above the circuit board. Andy |
The thing I don't see specified on the schematic, is the proximity between the wireYes, the standard "it's not what is on the schematic that you should be concerned about, it's what is not on the schematic" problem. -- Scanned by iCritical. |
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Hi,
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the theory is evident. I didn't reflect on the difference between the simulation and the original specification of the frequency in my image. I thought of the ideal characteristics of the simulation and why it does not work with this modulation. Is it possible to assign the induction separate to the leads or do I have to integrate inductors to every single lead? Thanks, CV --- In LTspice@..., "Helmut" <helmutsennewald@...> wrote:
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Something is wrong with that. The frequency should depend on the capacitance at that node (top of BB105 to ground). If it doesn't, then the oscillator transistor (the one on the left) isn't oscillating; the amplifying transistor (the one on the right) is. I think the oscillation in the left transistor happens because of feedback internal to the transistor, because no added feedback is shown on the schematic. This means that exactly what happens in simulation, is strongly dependent on the device models used for the transistors. I have splitted the coil into two parts and calculated the induction of Are the two halves also coupled, with a K ? Andy |
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Okay, thank you.
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I am absolutely confused how to handle this problem. :) The best way to find an answer is to ask my professor what he wants. He gave me this circuit and said: as a training you have to simulate this first. --- In LTspice@..., Andy <Andrew.Ingraham@...> wrote:
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For the most part you need to add little inductors in series with each component. There is no parameter or something similar that adds an inductance everywhere. Capacitors in LTspice do have an "equivalent series inductance". (Right-click on the capacitor.) The inductance remains hidden on the schematic. For resistors, if you don't mind messing up the schematic a bit, you can use an inductor to represent a resistor with series inductance, by entering the resistance value as the "series resistance". Unfortunately the resistance doesn't show up on the schematic. (Annotate your schematic well.) People can go overboard by adding stray inductance and stray capacitance everywhere possible. You might not want to do that. You probably only need to add it in a few places. Also, components have two leads, but the two lead inductors are in series with one another so you only need one inductor per component, not two. If all you are trying to do is simulate this circuit to see how it simulates (and not trying to replicate an actual circuit on the bench), then one might argue that you do not need to bother at all, with all the stray inductors. For the most part, the circuit SHOULD work without them. The biggest exception being that silvered wire. Inductances on the transistor leads might also be important for proper operation (I'm only guessing here). Regards, Andy |
Something is wrong with that. The frequency should depend on theDo you think I used the wrong models or the setup of my circuit is wrong? Are the two halves also coupled, with a K ?No they are not. I thought if it is a coil with tap I can separate it without using this. On the first hand I don't know how to use it. And on the second I thougt, if it's ideal conducting the K doesn't matter. |
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