# Tag Info

8

SMD chip inductors, compared to larger ones, will generally have: lower Q higher DC resistance higher SRF lower DC saturation current, if they're ferrite cored But read the datasheet and see if they'll work for your application. Often the higher SRF, smaller size and lower cost are the most important factors. For filter design trade-off, I'd suggest: ...

6

Any material with a relative permeability greater than 1 will increase inductance when inserted into a coil. Note that permeability is a complex number and frequency dependent. The imaginary part of permeability contributes to loss and appears as a resistance, so the addition of some material in the coil may increase inductance and also add resistance. ...

4

TL;DR: It's NOT mild steel, brass, or aluminum. I connected two different inductors to an antenna analyzer, and all of the above materials decreased the inductance as they were inserted. The larger the diameter of the steel I inserted, the lower the inductance and the greater the loss. It was the worst material I tried. When I inserted some powdered iron ...

4

I'm not certain of this answer, but this is my approximate understanding: Yes, the coiled-up ends form inductors at the ends of the antenna. But the ends of the antenna are the part of it where (almost) no current flows, only voltage builds up! Therefore no current flows through the inductor, and so the inductance has no effect. And if you're wondering why ...

4

A balanced mixer is one that suppresses the local oscillator (LO) input in the output. A double-balanced mixer (like the one you show here) suppresses both the RF input and the LO in the output. This is often accomplished with balanced transformers, hence the name. Because T1's secondary has a grounded center tap, the voltages on its two "hot" output ...

3

HF or not, toroidal transformers are pretty great. They'd be the only kind anyone would use were it not for: Fabrication cost. They are hard to wind with automated machines, since you have to somehow pass the end through the middle multiple times. Try winding one without ever letting go of the wire to see the problem. They have a lossy core. Ferrite ...

2

The value is specified as "large". The idea is to use the inductors to provide a DC bias without affecting the RF circuit. This works because an inductor has 0 impedance at DC, but increases with frequency. With a sufficiently "large" inductance, by the time you get to 434 MHz the impedance will be so large that it's effectively an open circuit. I wouldn't ...

2

Looking at T1, on the unbalanced side of the transformer, one leg of the input is tied to the chassis ground (the zero volt reference); the other leg is driven by a voltage source. Because the voltages on the two legs aren't equal but opposite, the input is said to be unbalanced. The current in the primary winding of the transformer creates a magnetic flux ...

2

It boils down to practical issues — you want to make it as small as possible, but no smaller. The power-handling requirements will dictate the wire diameter (to handle the current) and the end-to-end spacing (to handle the voltage). For an air-core coil, you also want the wire to be stiff enough to hold its shape well. You will want to wind the coil ...

2

As others have pointed out, the discrete components, suchs as capacitors and inductors, start to be quite challenging in higher frequencies. In general, transmission lines tend to have lower losses and higher repeatability around your frequency. Long story: While the transmission lines might be better for practical applications, I wanted to share the ...

2

One thing you might try is to add a fixed inductor in series with your rotary inductors to reach the overall required inductance. To maintain balance, I would wind two identical inductors, each on a toroid core with the same wire spacing. By using toroids, the magnetic fields are contained so that they don't couple to each other or to the rotary inductors. ...

2

There is also the matter of how much current the device needs to carry. A hand-wound coil made from a few turns of relatively heavy copper (compared to the off-the-shelf devices shown in the question) will pass a lot more current than a tiny pre-bought inductor. The ones in the picture look like 1/4W or so, but you could easily put 5W into a small hand-wound ...

1

Speaking only for myself... I have found air-wound coils to be relatively easy to make and tolerant of misuse. In the several instances I would have preferred to buy an inductor, I found it difficult to find something appropriate. So --for me-- it is mostly ignorance.

1

Here is a schematic for a simple, wide range balanced to balanced tuner: simulate this circuit – Schematic created using CircuitLab It consists of a 32 $\mu$H variable inductor (which you already have) and two double gang 470 pF capacitors. The voltage and current ratings will depend on the power levels you wish to run and the range of impedances the ...

1

In general, a choke would not be a good choice for this type of circuit as explained below. Given the relatively high frequency of your application, I would expect that you could find more suitable values or topologies for your impedance transformation requirement. Technically, the difference between a choke and an inductor is only a matter of application. ...

1

Inductors act analogously to a flywheel for electrical current. That is, they want to keep the current steady. To increase or decrease the current requires work, like speeding or slowing a flywheel requires work. They are the electrical dual of capacitors: capacitors do for voltage what inductors do for current. In RF applications, inductors (like ...

1

Would an inductor with SRF > 7 GHz and Q > 10 be okay at above frequency? Could it be made to work? I suppose. But any discrete inductor at 6 GHz is going to have significant non-ideal behaviors that you will need to model (or empirically measure) to get an accurate match. At the SRF the inductive reactance and capacitive reactance are equal, but this does ...

1

First thing first: Whenever you make an inductor, wire must be insulated for the working voltage of the circuit or higher. Otherwise, you get shorted turns and your inductor turns into jut normal conductor. Next, since you're high-school student, my advice would be to just use one of the calculators for coil inductance and get the results from there. One I ...

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