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8

To help identify a mystery ferrite core mix, the most common method is to take some measurements to determine the initial permeability (µi). Then compare your results to a table of µi for common core materials. This will put you in the ballpark and likely more than close enough to make an educated guess about the application(s) the ferrite core would be ...


7

No, adding ferrite beads to choke currents on the outside of the shield of a coaxial cable does not affect its impedance or velocity factor. Impedance and velocity factor are determined by the inside construction of the cable: the outside diameter of the inner conductor, d, the inside diameter of the outer conductor (shield), D, and the magnetic permeability,...


7

The basic operation can be understood by Faraday's law of induction. Any loop of wire will exhibit an electromotive force proportional to the rate of change of magnetic flux encircled by it. Since any electromagnetic radiation consists of both a time-varying electric and magnetic field, any loop of wire can theoretically be used as an antenna. The trouble is ...


7

The advantage of Litz wire —lower loss than solid wire— is realized below about 1 MHz. It is of little use above 160 meters. From https://en.m.wikipedia.org/wiki/Litz_wire Litz wire is a particular type of multistrand wire or cable used in electronics to carry alternating current (AC) at radio frequencies. The wire is designed to reduce the skin effect and ...


6

Following up on @dfannin's excellent answer: The most intuitive way of dealing with this would be: wrap your ferrite rod in halfway stable paper or so, something that certainly doesn't have high $\mu_r$ (gut feeling: baking paper is nice as it is very "slippery" on flat surfaces) make as many turns as you want around that; you're building a coil now, with ...


6

The K9YC paper you mention gives data up to 1 GHz on page 49: These data show for these core types the maximum number of turns is just one or two. Furthermore, it's quite difficult to achieve a choking impedance above 1 kΩ. That's not very much, and for many applications you'd want more. To get a higher choking impedance will require a larger core, and so ...


6

It appears that all three 'scope probes are set to their "X1" position. As such, each probe includes the oscilloscope's internal 1M input resistance in parallel with about 20pF input capacitance. But more importantly, the capacitance of the probe's cable is in parallel too. The total 'scope parallel capacitance is roughly 100pf. Since there are two ...


6

For well-designed coax, the EM fields are confined to the space between the inside of the braid and the center conductor, i.e. the dielectric insulation region which affects the velocity factor. Therefore, those beads have negligible effect on the differential signals. They do have an effect on the common-mode signals on the outside of the braid which has ...


5

When making a coax choke balun, does the size of the ferrite matter, and if so, why? Simplest answer: If the choke impedance is low enough to allow some common mode power through, then there is a possibility of overheating. The bigger cores either dissipate heat better or provide higher impedance. Another way to say the same thing: As long as the choke ...


5

The primary issues with coax wound common mode chokes are; The inductive reactance of the choke can cancel out the capacitive reactance associated with the feedline shield thereby worsening the CM situation The resistive component of the choke is not sufficient such that the core undergoes an undesirable temperature rise The interwinding capacitance forms a ...


5

I don't think it will work to add suppression to the fence. The fence charger is designed to support heavily reactive loads by generating pulses every second or two. The pulses are formed by dumping the charge of a capacitor bank through a step up transformer. Any additional reactance will be a very minor load delta. My experience (several miles of e fence ...


5

you're on the right track to measure/calculate effective permeability. However, you need to use an inductance meter that can measure up to 1 nH accurately or so. If you're trying to use one of those $25 LCR meters , it won't have the accuracy or precision you require, plus you won't be able to zero it. Another issue is that you'll have a wide variance ...


5

I've had a couple turn up cracked when left outside in an enclosure that wasn't waterproof, but I can't say if that was freezing that did it, or just thermal cycles on a compromised toroid causing stress. These days I hit pretty much all of them with a light coat of decent spray paint, or even a light coat of flex-seal type sealant before putting them ...


5

For the purposes of amateur radio, ferrite materials are usually useful for making inductors where an air-core coil could not feasibly achieve the necessary inductance. Three relevant questions which the datasheet can answer for us are: what inductance will a coil on this core have? what losses will this core material introduce? at what current will this ...


4

"Ferrite" is not a fungible material. There are many kinds of ferrite materials, each with very different properties. To make a comparison, you need the material datasheets, which answer questions like: What is the relative permittivity? What is the loss at the frequencies you intend to use them? What is the Curie temperature of the material? You can see ...


4

That does look like a fine core to use, and the photo of your construction looks good. Your coax isn't causing any problems with noise. Try putting the choke at the feedpoint, not at the radio, in lieu of the ugly balun you have now. A choke at the radio will do little since the coax shield, connector, and enclosure of the radio already form a continuous ...


4

SPICE modeling shows that replacing T2 and R with a 22.2-$\Omega$ resistor, the impedance looking into T1 is indeed 50-$\Omega$, as expected: Similarly, replacing the 50-$\Omega$ generator and T1 with a 25-$\Omega$ generator shows that the impedance looking into T2 is 25-$\Omega$: This is a result of the electrical symmetry about a "virtual ground" ...


4

No. At best it will do nothing; if it did something, it would probably turn your roof from a relatively good reflector (which may mess with your SWR, and may distort your pattern, but the energy that doesn't go where you expected it at least goes somewhere) to a relatively bad reflector (which absorbs energy from your antenna and turns it into heat — ...


4

A ferrite core used for radio is specially constructed to conduct magnetic fields while not conducting electrical current, especially eddy currents. A slinky is (typically) an uninsulated conductive coil of variable spacing, and thus variable inductance. It is nothing like a ferrite core. Typically they are made of steel which his high resistance (for metal)...


4

Now if I imagine the coil without the ferrite but I multiply the area by 1000, that will be a huge area, how can it be 1000 times more power? Because, as the article says, the magnetic permeability of the ferrite rod is much higher than that of air, and thus it concentrates the magnetic flux from a large area around the antenna. [Ferrite Antennas for A.M. ...


3

So the problem here is that your setup is not sufficient to tell you what you want to know about the ferrite core. In my set up I have a ferrite core where I made a number of turns on. I connected the signal from my signal generator and one channel of the oscilloscope to one end of the wire to monitor the input. So in this setup your first probe is ...


3

The answers here are excellent and I have little to add other than to emphasise / RFI problems are hard / Consider the case of the RFI problem discussed in Electronics Stack Exchange ( https://electronics.stackexchange.com/questions/402021/how-do-i-specify-a-low-rfi-led-driver/402029#402029 ). Everything has been ferrited to death (5000 ohm common mode ...


3

As it's name implies, a loopstick antenna is a magnetic loop antenna and is one of the best choices for an electrically short antenna; necessary because broadcast AM wavelengths are hundreds of meters long. Rather than a regular loop, a loopstick utilizes a large amount of (usually Litz) wire wrapped around a ferrite rod. This forms an inductor which is ...


2

Transformers are inductors. They just happen to have mutual inductance with another inductor. Like inductors, they also have self-capacitance, and so a resonant frequency. They also have loss, and consequently some maximum power handling ability which if exceeded causes the transformer to fail by overheating. As such, any parameter which is relevant to an ...


2

Permeability is the measure of the ability of a material to support the formation of a magnetic field within itself or more simply, the inductance per unit length. Magnetic permeability is typically represented by the Greek letter μ (mu) and is measured in henries per meter. It's helpful to remember that inductance here is a complex number. In the context ...


2

Because ferrites aren’t marked, it is difficult to know what frequencies they work on. However, now we can use the popular NanoVNA along with free software (and Excel) to graph the unknown ferrite’s impedance over frequency. YouTube video by Fair-Rite Corporation, using a Nano VNA and software: https://youtu.be/KmKQibSDzqM (Sorry that more info from this can'...


2

Looking at an Amazon listing, it appears that the Degen 31MS active antenna has three ways to connect to a radio. The first is via a direct ANT jack, the second is via clips to existing wire (likely telescoping) antennas, and the third is some sort of ferrite bar coupler that you're mentioning. A brief search didn't bring up a user manual or anything like ...


2

I believe the choice of the core size is twofold. As from K8NVH good answer a minimum impedance is needed for the balun to do its job. A common mode impedance much higher than differtial ones involved makes sure the balanced to/from unbalanced convertion takes place. This somehow drives the size of the core for its mechanical dimensions shall allow the ...


2

Nearby antenna elements do affect each other. Consider a Yagi-Uda. Pointed in the "wrong" direction, the director and reflector elements will reduce the EM power that the driven element receives from the impinging RF field. However, a parasitic loop can often increase the power to a nearby small radio antenna, rather than steal (or "zap"...


1

The very best source of information that you'll find about making common-mode chokes is available at Jim Brown, K9YC's site http://k9yc.com/publish.htm. Download his PDF http://k9yc.com/RFI-Ham.pdf. RFI, Ferrites, and Common Mode Chokes For Hams Most recent update April 2019. This tutorial is directed specifically to RFI in ham radio applications. It ...


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