New answers tagged

1

That answer does not make sense. If you have a typical AC audio signal, and you cut off the lower half of the waveform, say with a diode, you have a DC signal of no greater power. Plus, current is at zero for half of the time, therefore it would enjoy the same OR BETTER cooling time as the full AC. The only real difference then is that the natural tension of ...


2

The following points are to be taken care of while building the foxhole radio. Wire antenna around 60 - 120 feet long. A good earth connection to a buried water pipe. Coil former 1.5 - 2" in diameter. 75 to 125 turns of 25 SWG enamelled copper wire for the coil ( greater the former diameter, lesser the turns). Enamel stripped over the coil length ...


2

I don't know your speaker, but you have to realize this kind of receiver has a very high output impedance: there's nearly no current this can supply to the speaker. Also, you won't be able to see audio-frequency AC voltage with your voltmeter. You'll need an earpiece (usually, not something you'd call a "speaker") that has a very high impedance. ...


1

I think, looks like to me and forgive me if I am wrong, you confuse modulation signal (the information you want to obtain) and carrier that is the high frequency signal which its amplitude is modulated. Again, if I am not wrong, when you refer to the range 20~20000Hz you refer to audio signals that is the usual bandwith. The 20KHz can be managed by any opamp ...


0

The transformer gives gain without noise, but you can replace the diode with an LM1496 balanced Demod with 85dB carrier suppression. An Op Amp demod is too noisy and poor carrier suppression at 1MHz due to lack of GBW. GBW must be 300 MHz for transadmittance to get this performance.


0

A mains-operated radio would be earthed to enable ground-fault tripping that would render it safe from electrocution hazards. Likewise, an antenna too could be earthed to provide a safe path for static charges, accumulated on it, to ground. At low frequencies and good ground conductivity, a grounded ¼ λ antenna would be used without an extensive ground ...


0

Not all radios need to be grounded. The cell modem in your mobile phone is not grounded. The radio transceivers in a satellite are not grounded. Radios receive electromagnetic waves that pass by the antenna. At the antenna the intensity of the electric and magnetic fields are changing with time. But changing with respect to what? That's why you ground ...


3

Often we don't actually ground them, but the ground symbol is just a design convention. If we had to ground them, then we couldn't have radios in aircraft or spacecraft or make portable hand held ones. The conceptually simplest radio antenna is a dipole, which consists of two wires running in opposite directions, operated in opposition to each other. Often ...


0

I think that the ground in the schematic is just a voltage reference point. Here is a schematic diagram of a handheld flashlight (torch). simulate this circuit – Schematic created using CircuitLab


0

Lower frequency waves travel further as surface waves. They tend to follow the earth's curvature due diffraction and attenuation. Diffraction causes bending and is inversely proportional to the wave's frequency. Attenuation, along with energy loss, also makes the waveform to tilt downwards. This essentially helps in following the earth's curvature. ...


0

This is an AM radio demodulator. The L1 of RF transformer along with Cvar1 adjust the tuning frequency of incoming RF signal. The diode and C3 and R2 together form an "envelope detector" which extracts the envelope of the RF signal (u can google for envelope detector). The first OPAMP is just a buffer with a gain of 1. The next two opamps amplify ...


1

A compact (roughly measuring 3/4" x 1/2 "), 1 MHz 'canned' crystal oscillator may be used. It's also known as a DIL 14 oscillator, available in 5 V and 3.3 V versions. When plugged into a dual-in-line 14 pin socket, the pin numbering would be 1, 7, 8, 14 instead of 1, 2, 3, 4. A metre long piece of wire could serve as an antenna considering the ...


2

I am still wondering if that is physically possible to make it work for very short distances like in my bench and without the requirement of large and complex antennas A short monopole will work fine if you have a half decent earth. Alternatively, a short dipole will work at either end of the link. At circa 6.8 MHz, the wavelength is about 44 metres and a ...


5

Neither. Satellite radio such as Sirius transmits the digital data with COFDM-DQPSK modulation.


5

You can regard your long steel pipe as a waveguide. There are four principal ranges for RF frequency to consider when trying to transmit an RF signal along a pipe a) waveguide below cutoff b) single mode operation c) operation with a few modes d) operation with very many modes The two lowest frequency modes for circular waveguide are TE11 and TM01. In a pipe ...


1

I also unfortunately have no answer, but perhaps these comments help the OP along. The reference by @VVT (https://www.netl.doe.gov/sites/default/files/2018-03/FG113004.pdf) is quite applicable, as it includes not just signal strength measurements but also a modem test for a 24in steel pipe over about 1 mile. The OP is cautioned not to equate signal strength ...


3

Being in essence just a reference, this info is more relevant as a comment to your question. With cited quotations (for your convenience), the text is too long to be included in a comment. Please understand that this "answer" is just a comment. Pipelines as Communication Network Links Abstract ... The work addressed the need to develop secure ...


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