OH2FXN
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How does a "chip antenna" work?
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8 votes

The chip antennas use some material, usually ceramic, that has high permittivity and low losses. In a medium having high permittivity, the wavelength is shorter than in the free space. This way the ...

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Understanding RG6-75 ohm Cable Impedance
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5 votes

You have mixed up the characteristic impedance of a coaxial cable with the DC impedance measured from a piece of that cable. So I'll tell you what you measured and then what you could have done ...

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If two antennas of 50 Ω and 377 Ω have VSWR=1:1, then which one is more efficient?
5 votes

The antenna efficiency refers the ratio of radiated power and the power fed to the antenna. The rest of the fed power is transformed to heat by the losses in the antenna. Thus, the antenna efficiency ...

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Demodulating ISO14443 (part of NFC) using SDR?
4 votes

This isn’t a solution to your problem, but I had similar challenges with UHF RFID at 865 MHz. In UHF RFID the tags are electrically short dipoles modulated by the chip impedance. I thought it would ...

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Can a person in Portugal get an amateur radio license in another country?
4 votes

I don't have the full answer, but I hope I can give you some pointers on where to search. If you get a HAREC (Harmonised Amateur Radio Examination Certificate) license in any country that complies ...

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Can I filter after modulation when using a square wave oscillator?
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4 votes

Filtering square wave aims to produce as pure as possible sine wave as the local oscillator frequency. If you would feed all the harmonics to the non-linear modulator, the output would contain all the ...

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Is the 3-cm band serviced by any commercial main-stream ham radio transceiver?
4 votes

At least in Finland you are allowed to use the entire band from 10.0 GHz to 10.5 GHz with "secondary rights". Maximum TX powers are 30 W (basic class) and 150 W. The 3 cm band is also available at ...

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How to increase the range of the spectrum analyzer in SDRSharp?
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3 votes

Unfortunately you cannot increase the bandwidth much: the sampling rate in RTL2832U is at maximum 3.2 megasamples / second. In theory (Nyquist theorem) you could get ±1.6 MHz banwidth, but that is ...

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If I parallel two crystal filters together, will that double the bandwidth?
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3 votes

As pointed out, the short answer is no. The Q value for the series resonance of a crystal can be calculated from $Q = \frac{2\pi f_s L_m}{r_m}$. Q value is of course related to the bandwidth: $Q = \...

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How to design a rubber ducky antenna
3 votes

The rubber duck antennas are monopole antennas that have their length of wire turned into a helix. The helical shape allows you to cram the same length of wire into a smaller volume, just as you ...

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Does propagation affect magnetic and electric fields equally?
3 votes

In a traveling plane wave the ratio of the electric ($\vec{E}$) and magnetic field ($\vec{H}$) is always the wave impedance of the medium (377 $\Omega$ for air or vacuum). Further, the fields are ...

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Will swapping receiver polarity on a spiral antenna change right hand to left hand polarization?
Accepted answer
3 votes

What do you mean by reversing connection? If you just swap the ground and center wire of the feeding coaxial you create 180 phase shift, not change the polarization. The polarization of a helix ...

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What is really happening during RF ionospheric refraction?
2 votes

The ionosphere contains freely moving charged particles that act like a conducting "plate". When a radio wave traveling up reaches the ionosphere, the electric field of the wave starts to move the ...

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Does the impedance along a transmission line change when there are standing waves?
2 votes

Yes, the characteristic impedance of the transmission line $Z_0$ does not change (it is a property of the cable itself), but the impedance seen from the end of the cable depends on the length of the ...

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How to choose right inductors for a matching circuit
2 votes

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 ...

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Frequency selective surfaces working principle
Accepted answer
1 votes

You had three separate questions there, I'll try to clarify some concepts: How can a time - varying magnetic field induce current in vertical strips Faraday's law of induction tells us how much ...

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How would I calculate aperture efficiency for an antenna?
1 votes

For any antenna, also for wire antennas, you can calculate so called effective area with $A_{eff} = \frac{\lambda^2}{(4\pi)}G$. An ideal antenna with surface area of $A_{eff}$ absorbs the same amount ...

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How much field strength to blow out a receiver?
1 votes

A major edit to my original answer to capture the comments below. The Friis equation, that I originally suggested, does not apply in this situation since the receiving antenna is only around one ...

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Resistive impedance with frequency
1 votes

Yes, you are correct: both resistive (real) and reactive (imaginary) part of the antenna impedance change as function of frequency. However, near the resonance of the dipole the reactive part changes ...

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Why does ice on a wire dipole affect the SWR?
1 votes

The increasing SWR means that some of the transmitted power is reflected back to your transmitter. There are several possible explanations for the effect: The ice is not completely dry and it ...

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