hotpaw2
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change LC parameter digitally
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2 votes

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 ...

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Not able to understand some operations in rtlsdr library in python
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2 votes

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 ...

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Can SDR receivers be detected remotely?
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A direct sampling SDR does not need a LO anywhere within the frequency range or tracking the signal of interest. A processor running off of a fixed clock frequency well above twice the RF signal ...

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If receive performance doesn't depend on SWR, then how can I tune my manual HF antenna tuner by band noise?
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You can get a good match by maximizing received noise, because that is the point where more RF noise might be transferred from the antenna to your receiver, and thus indicate where the SWR is lower (e....

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Does Kirchhoff's current law (KCL) apply to antennas?
2 votes

You are not considering distance, time, frequency, and the speed of light (or EM propagation) being finite. If the current flowing into on end (point A) of a segment of wire changes, that change won't ...

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Loop Antenna Construction
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Partial answer to part 1 of your question. Yes, the loop created by the open space between the ground lead of your scope probe and the probe tip acts as a small (parasitic) loop antenna. But mostly ...

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Understanding how quadrature heterodyning captures information from negative frequencies
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Negative frequencies in the real (single DOF measurement) world are just what we call positive frequencies that happen to below some other frequency. Above baseband, that LSB signal isn't really ...

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rtlsdr - hearing an FM broadcast on different frequencies
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Likely 5th order IMD (inter-modulation distortion), caused by a strong signal mixing with the 4th harmonic of another frequency (internal digitally synthesized signal or oscillator) related to the “LO”...

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Transmitting Video Underwater
2 votes

Any antenna under water is creates a far more difficult problem than that of the main focus of the school project. I would put a WiFi transmitter (ESP32, et.al., inexpensive loss if drowned) on a ...

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How can a tuner pick up a specific frequency?
2 votes

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 ...

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Why is outer coax usually grounded?
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One important reason is safety. One wants the exposed metal part of the coax connector to be at the same potential as the Transmitter case at one end, and any grounded equipment at the other end. Not ...

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Why can I hear Morse when not in CW mode?
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Morse Code is a timed on-off signaling method that is not restricted to CW radio, as it was invented decades before Maxwell hypothesized the existence of radio waves. Morse Code can be used for ...

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I can copy 15wpm how to to continue?
2 votes

Some random untested ideas: Don't get stuck using just standard spacing/timing. Variation (data augmentation or novelty) proves effective for both machine learning and human learning. It's also more ...

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Vertical Hustler - do I need any radials?
2 votes

The Hustler web site says: "For optimal performance, radial wires should be used." Somewhere else, there is a recommendation for sets of 3 tuned radials per band on which you plan to operate. A ...

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SDR transmit on more than one frequency
2 votes

Yes. A direct conversion SDR (one with an ADC and DAC that covers the entire HF band, for instance) might be able to transmit not only on multiple frequencies, but with custom firmware/gateware, ...

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What causes the light and dark bands (of background noise) in an HF waterfall display?
2 votes

Often, the source of bands of noise in an SDR spectrum is locally generated RFI or EMI. During a neighborhood power outage, one might notice a large number of these bands disappear. Sharper bands in ...

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How is frequency selection (tuning) accomplished in a direct conversion receiver?
2 votes

For single-channel direct-conversion to baseband, tuning is done by setting the heterodyne or mixer oscillator frequency, and possibly by tuning band-pass filters, if any, in front of the direct-down-...

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Why does an RF Amplifier fail when the SWR is high?
2 votes

I like to turn the question around. Why does a transmitter amplifier not burn up or fail? There's power coming into the transmitter from the power supply. Why doesn't it melt the transmitter? ...

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Synchronizing HackRF Ones at a distance
2 votes

First synchronize all 4 clock generators in frequency using an external source (say, GPS or atomic clock derived into the 10MHz ref input). Start receiving continuously on all 4, and use the received ...

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Improve AM reception on an old Walkman that has no external antenna
2 votes

A tunable high-Q loop antenna, such as: https://www.amazon.com/Kaito-Tunable-Passive-Antenna-Panasonic/dp/B001KC579Q/ placed near your small AM radio can inductively couple into the internal ferrite ...

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Does scanning take much more battery than listening on one channel?
2 votes

I would not be surprised if the audio amp used more power than the rf front, tuner osc, and signal detect combined. Thus listening at some reasonable speaker volume, and using energy to vibrate a ...

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Is the Nyquist rate independent of the power of the analog signal being digitized?
2 votes

Theoretically, the rate is independant. In reality, exceeding certain power levels will cause real world digitizers to increase in non-linearities (clipping, saturation, thermal damage, and etc.), ...

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If someone transmits on 151.88 MHz and I listen on 151.18 MHz, how likely would I hear their transmission?
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2 votes

It's possible for a strong enough interfering RF signal to overload the front end amplifier(s) of a receiver. Once overloaded into a non-linear range, all bets are off as to the resulting bandwidth ...

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How to operate on HF if an AM transmitter is only 540 feet away?
2 votes

Assuming the AM station doesn't wipe out your internet connection, how about setting up a remotely operated HF rig far offsite (friend or relative's house, etc.)?], and operating it from your home ...

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Bandwidth of a CW signal?
2 votes

Answering my own question: First, the question was ambiguous, as it does not differentiate between (1) the bandwidth required to transmit the information, (2) the bandwidth required for the typical ...

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Why prefer LC oscillators rather than RC oscillators in RF design?
2 votes

The transient response of an RC circuit driven to oscillation by negative feedback generates a much higher proportion of harmonics than a similar LC circuits response. These harmonics have to be ...

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How can I know over what distance or at what speed I can communicate?
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2 votes

Shannon's law on information communication provides statistical upper limits on data rate given a signal to noise ratio: S/N. There may be nice physics models on the power coupled between a pair of ...

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Why are some electrical contacts gold plated?
2 votes

Surface conductivity that changes less over time after exposure to an oxidative environment (normal room air). Some oxides are insulators, the opposite of what most connectors are usually meant to ...

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Why do satellite tracking programs have to be updated?
2 votes

Some of the factors, such as friction against the upper atmosphere, can have the same sort of predictive problems as with lower weather prediction (non-linear dynamical "chaos", or sensitivity to ...

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What is morse code used for in amateur radio?
2 votes

Amateur radio operators still use Morse Code, as do a few other government services, such as aviation beacons, etc. These Morse Code signals are usually just encoded text (roughly related to other ...

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