Tag Info

8

These were common abbreviations in use for Components, Radio equipment, and Printed publications in the 19th and most of the 20th century. Mfd = microfarad or μF kc = kilocycles or kHz. 1,000 cycles per second. μμf or mmf = pF (picofarad) Frequency The change from kc to kHz and mc to MHz were done because someone though that Heinrich Hertz ought to be ...

7

That's an expected phenomenon: Real-world physical systems tend to be frequency-selective (i.e. not constant over frequency), and "at large scale" low-pass systems. This applies to amplifiers, mixers, oscillators, and even transmission lines and connectors. So that's normal. Ettus even publishes exactly such measurements at https://files.ettus.com/...

6

Don't worry, there have been many researchers before you, and you can borrow some of their work. Your English is fine. If you do a web search for "lightning spectrum", you will find a graph showing lightning intensity vs. frequency. The range of frequencies emitted by lightning discharges is very broad. From amateur radio experience I can tell ...

6

Because mathematically, a function like $\sin(\omega t)$ has an angular frequency of $\omega$ and $-\omega$. Consider: $$e^{i\omega t} + e^{-i\omega t}$$ By Euler's formula this can be expanded to: $$\cos(\omega t)+i\sin(\omega t) + \cos(-\omega t)+i\sin(-\omega t)$$ By the trig identity $\sin(x) + \sin(-x) = 0$ this simplifies to: $$\cos(\omega t)+ \... 5 Baseband video is the DC to about 6 MHz signal that encodes the brightness channel, and sync. If it includes colour too then it's called Composite video. Brightness and sync are truly baseband, a specific voltage range represents the black to white brightness over time as the beam scans the display, with sync represented by pulses to a different voltage. ... 5 The number of cars is not an issue. Driving in a city with thousands of cars in your vicinity still allows FM reception. Engines are running, which is probably not the case when watching a film in a drive-in cinema. For good stereo reception (26 dB audio signal to noise) you need a field strength of 100 µV/m or more. In a Rayleigh path with reflections you ... 5 The frequency allocation chart is really more artistic than informative. You can not and should not use that as a guide for selecting a frequency. There is too much information to fit on the chart, and as much as is there anyway, it's not surprising you feel lost looking at it. (That may be part of the intention of the chart.) There are multiple bands ... 5 The wavelength at 1 Hz is several times greater than the circumference of the Earth. At these frequencies, one arguably can't even have an "antenna" for terrestrial communication, since any two such antennas would be so close together they would be more like two plates of a capacitor or two windings of an inductor than an antenna. 1 Hz isn't even ... 5 Yes. You're looking for a transverter that will take RF from one source (your radio) and treat it as if it were an IF stage into another system. Here is an example. Obviously, you'll need to take care that you have operating privileges at the output of the transverter, including making sure spurious emissions are appropriately suppressed, etc. 4 A bolt of lightning has an average center frequency of about 16 kHz, which varies with the height of the bolt. This is a distant stroke that I captured on one of my SDR lightning receivers, using three 4-turn 1-meter dia. vertical loop antennas, spaced 120° apart: (Ignore the apparent 50 mV offset) Note how the energy on this particular stroke is ... 4 That's just the math behind it – everything is alright with these results! You need to write down the formula of the real-valued \sin(t) in terms of e^{j2\pi t} and e^{-j2\pi t}, and you'll see that, as shown in your plots, the real-valued harmonic oscillations have a positive and a negative frequency component – so multiplying two of these yields four ... 3 Transmission between antennas is "two port in to two port out". But: in between there is a transmission path with reflections. Some frequencies are attenuated and some other frequencies are even stronger than average. That is called Rayleigh path (sorry, not complete for the moment). The transfer is frequency-dependent AND antenna position ... 3 A lot of the RTL-SDR code is open source on GitHub. This code runs just fine on a Raspberry Pi 3B or 4. The C code inside rtl_tcp to set the frequency is only a few lines long. From a remote system, after starting the TCP connection, send 5 bytes, 1st command byte 0x01, then 4 bytes containing the desired frequency in little-endian 32-bit integer format. ... 3 If you approximate the yellow trace as a rectangular function:$$ \text{rect}(ax) $$then the Fourier transform of this is:$$ {1 \over |a|} \cdot \text{sinc}\left(\xi \over a\right ) Of course, a lightning impulse isn't exactly a rectangular pulse, but I suspect that does not substantially change the character of the frequency response: infinite, with ...

3

There's multiple way that multiple signals can be sent at the same time on the same frequency. One is to have multiple antennas, where even though the antennas themselves can be omnidirectional, they can be used to "beam form" by carefully offsetting the signal. And likewise the receiver can do this trick. Also see this article on MIMO. Wifi can ...

3

The frequencies in your pasted image of a table are in kilohertz (kHz). These days frequencies are more often expressed in megahertz or gigahertz (MHz or GHz). Anyway, frequencies ranging from 3560 kHz, also known as 3.56 MHz, to 15.245 MHz are in the high-frequency (HF) band, also commonly called "shortwave", rather than the very-high-frequency (...

3

Gnu Radio doesn't really know anything about frequency in cycles per second (Hz), only cycles per sample. The left of the chart is -0.5 cycles per sample, the middle is 0 cycles per sample, and the right is +0.5 cycles per sample. It's up to you to enter the correct numbers for "bandwidth" and "center frequency" if you want the scale on ...

3

This is a consequence of what was discussed in your previous question, that any real-valued function like $\sin(\omega t)$ consists of both positive and negative frequencies. Multiplying by a complex exponential $e^{i\omega t}$ simply shifts frequency by $\omega$. There are many ways to show this, one way is to simply look it up in a table of Fourier ...

2

Radio waves are waves, which have many similarities to other waves, which allows us to consider analogies. Here's one: if you put your ear firmly to the end of a long tube, the sound will be different than if you weren't listening through the tube. Instead of hearing the usual mix of high-pitched sounds, low-pitched sounds, and mid-range-pitch sounds, you ...

2

Consider a swing, like the kind found at a playground. If you sit on it and shift your weight forward and backward at just the right rhythm, you can get the swing to go very high. It goes high because the combination of the swing and the mass of your body is resonant at a particular frequency. When you shift your weight to "pump" the swing, you add ...

2

I am jumping in late, and I hope that the OP received an out-of-band answer, or found their own answer. I have a problem with the question, given the statement that the OP is using a Kostas Loop for the demodulator. By definition, the Kostas Loop is a type of phase-locked loop (PLL) in which the local oscillator (LO) frequency is adjusted until the phase ...

2

It's not like mixing paint. That's because it's a just a simple sum or linear mix, rather than a chaotic or non-linear mix with intermodulation products. It's like a duet with a soprano and a bass singer. You can easily transcribe the low frequency bass voice and semi-ignore the soprano, or vice versa, because the frequency ranges are so different, and ...

2

There's something called the "principle of superposition" — in a linear system (which we can consider an antenna and the "front end" of a receiver to be), if the current resulting from signal A is $C_A$, and the current resulting from signal B is $C_B$, then the current resulting from both signals at once is simply $C_{A}+C_{B}$. Even if ...

2

More than one block can be read into the psd if you want a result that is averaged (thus usually smoother) over several blocks. A sample rate in Hz can be divided by 1e6 if you want a spectral plot labeled in MHz, instead Hz.

2

Perhaps you are thinking of a switched capacitor filter? Unfortunately, most switched capacitor IC components are (were) designed for audio frequencies, not VHF. Another possibility is to use an LC tuned circuit containing a voltage controlled varicap diode capacitor, controlled by a (digital input) DAC. As per the earlier answer, you can use a use a ...

2

The real number of samples from an RTL-SDR is not available via the USB interface. The RTL2832U chip samples at 28.8 Msps, but then mixes and downsamples the internal samples to lower rate IQ samples at from 240k to about 3 Msps, to allow transport over its slower USB 2.0 bus. The front-end R820T tuner can first downconvert VHF and UHF signal to a low HF ...

2

Common solution for this problem is the setting of the frequency step size. That must be different from 25 or 12.5 kHz. Grid step must be set to 20 kHz or 10 kHz or 5 kHz. According the technical description that is possible. Scroll to that specification point: "Frequency Step: 2.5KHz/5KHz/6.25KHz/10KHz/12.5KHz/20KHz/25KHz".

1

A "simulated inductor" might work in your application: You could adjust the simulated inductance by using an analog multiplexer IC and resistive ladder array IC to change the values of RL and R1.

1

Frequency setting and control can be achieved with a phase locked loop (PLL). The frequency of the oscillator is compared to a known and stable reference frequency. Look for further explanation with search terms: radio PLL, RF synthesizer and frequency stabilisation. Digital control of frequency: fractional PLL and All Digital PLL. See picture. Copyright? I ...

1

The number of samples to read. Probably because whoever wrote it wants the graph to read in MHz rather than Hz.

Only top voted, non community-wiki answers of a minimum length are eligible