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    Diameter of imperial machine screws

    Dear Forum, I am currently trying to buy some imperial machine screws and bolts online, and I am confused with how the diameter is given. The website I am seaching ( gives me these diameters but I don´t understand what is meant by i.e. "2-56" 2-56 4-40 6-32 8-32...
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    Isolation Transformers and Electrical Safety

    Hi, An isolation transformer is used in order to "safely" separate one part of an electric circuit from the mains. (description in" [Broken]) Still I have problems grasping the important concept of such a transformer. I have spent some...
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    ESD Protection

    Hi, I have a switch connected to a motherboard. During ESD test with 8000kV (directly on the switch) the ESD spike caused my system to reboot, and I need some kind of surge protection betwee nthe switch and motherboard. I am not sure what I need to look for? Can anyone suggest a...
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    Op-Amps for ECG Monitor

    Dear Forum, I would like to build my own ECG monitor. Does anyone have experience building one? Especially I am looking for recommendations on which op amps I can use. The ones I have found, like TI's ina122, ina 332 are both rather expensive (like 10 euro per piece) and hard tu find...
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    Coupling between tuned circuits

    Hello I have two resonant circuits (tuned to the same frequency) that are magnetically coupled to each other via two coils placed paralell to each other. (energy and data is transferred from one circuit to another) Now, I know that the coupling between the two can be overcoupled...
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    PU resin

    Dear group, Can anyone tell me what kind of material PU Resin is? Is resin a material or just a "spacification" of PU? regards t.
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    Superposition of magnetic fields

    Hi a short question: can I use the superposition principle for magnetic fields? reegards tem
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    Source (inner) resistance

    Dear Group, I need to simulate a HF circuit (matched to 50 ohm ) connected (via a 50 ohm coax cable) to a signal source with 50 ohm output resistance. Simulating this with e.g. Spice, should I use a 50 ohm resistor in series with the source? Does the fact that the source is matched to 50...
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    Pcb design software

    Dear Group Does anyone have experience with any good freeware for designing PCB? regards eirik
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    Loading of transformer

    dear all, When loading the secondary winding of a transformer, my textbook gives the following relationships: \frac{V_{sec}}{V_{pri}}=\frac{N_{sec}}{N_{pri}}\\ and \frac{I_{sec}}{I_{pri}}=\frac{N_{sec}}{N_{pri}}\\ Do these relationships hold also when the diameter of the windings are...
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    Q-factor in resonant RCL circuit

    Dear Forum, I am not sure how I can calculate the Q-factor in the circuit attached. (The circuitresonates at 13.56MHz and tuned to 50 ohm input impedance, thus the two capacitors) Is the Q-factor of the circuit simply Q = \frac{\omega L}{R_{a}+R_{coil}} ? I went through some examples...
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    Resonance in a coupled circuit

    Dear Forum, My question is to the circuit drawing I have attached. (representing a simplified rfid system, with "Circuit 1 being the tranceiver antenna, "Load" being a transponder and "Circuit 2" represents an additional circuit between) ... For optimal performance the circuit should...
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    Magnetic Field Lines

    I always thougth the "dotted lines" illustrating the direction of a magnetic field were only a tool for vizualizing this direction... Now I read that the definition of a weber equals 10^{8} field lines. So does this mean that the field lines really exist as discrete lines along the direction...
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    Magnetic Field Density

    Hi My textbook denotes the magnetic flux through a single turn loop as \Phi, and the magnetic flux density in the same loop as B = \frac{\Phi}{Area}. Extending to an N-turn loop the total flux passing through the coil is given by \Psi = N\cdot\Phi \leftrightarrow \Phi = \frac{\Psi}{N} ...
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    Impedance of load

    Hi, I have some problems in understanding how to calculate the input (is it input?) impedance of a small circuit. (I have attached the equiv. circuit with values ) The circuit is a small loop antenna that resonates at 13.56 MHz and is tuned to 50 ohm. From the source point of view: a...
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    Basic question on input impedance

    Hi, I have a HF transmitter rated with 200mW output power. An antenna is connected to the transmitter via a 50 ohm coax cable. (The antenna is also matched to 50 ohm.) Does this mean that from the transmitters point of veiw, a 50 ohm resistor is connected as load? Can I find the current...
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    Electromagnetic Field, H vs. B

    I have a problem understanding the meaning of magnetic field strength, denotet H. I have the following example from a textbook: 1. The path of magnetic field strength developed in a conductor loop is given by the formula H = (I*N*R^2) / (2*sqrt(R^2+x^2)^3) I = current N=number of turns...
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    Practical impedance matching

    Hi, I have a few 50 ohm loop antennas tuned to resonate at 13.56 MHz. (inductive RFID antenna). I would like to test one antenna´s influence on the other, so I think one approach is to connect one antenna directly to a signal generator. Do I have to design any matching circuit between the...
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    Jet planes´ tail

    Hi, Sometimes when a jet plane is flying above you you can see the white tail from the motors, and sometimes not. What is the reason for this? Why isn´t this visible all the time? regards t.
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    Confused with dB conversions

    Hi I´m a little bit confused regarding conversion to dB: Regulations for a project I´m on say the maximum magnetic field strength allowed is 60 dBuA/m at 10 m. (here I chose 60 myself for simplicity...) So the question is will this correspond to 1 A /m at 10 m (10log[1000000/1]=60 dB)...
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    Xor of multiple bytes

    Hi, Short question, I have to XOR multiple bytes. Is the right procedure to XOR first and second byte then XOR the result with the third byte and so on? Or is there a different method? t.
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    Why do the tuaregs wear dark blue?

    Why do the tuaregs wear dark blue..??? Hi, I tried to find a suitable forum for this question...this seemed to be the most appropriate. The Tuaregs living in the Sahel/Sahara region in North Africa cover their body completely in dark dark blue clothing. A long time ago I read somewhere...
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    RFID Antennas with ferrite Rod

    Hi, I have a question relating to RFID antennas... For inductively coupled RFID systems, the max. range is about 1.4 times the diameter of the sender antenna (for a loop antenna). In low frequency systems (125, 134 kHz) the antenna coil is often wounded around a ferrite rod, making the...
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    Simulation of near field

    Hi, I´m looking for a program (free or cheap download) that can simulate the nearfield of a coil/ field of inductive antennas preferably in 3D. Does anyone know if such a thing exist? t.
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    Magnetic fields / RFID

    Hi First, I´m new in this forum so I´m not sure if I´m posting in the right place. If I don´t.....well, sorry. Then my question...I´ll try to explain. I´m playing with an inductively coupled RFID-reader and smart labels. Holding the smart label 90 degrees with respect to the antenna...