hotpaw2
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Can I wind my 9:1 unun with two wires instead of three?
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Using triple windings allows closer wire spacing between the transformer input and output (primary and secondary) windings which can improve the magnetic coupling coefficient. This can slightly ...

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What comes first, Voltage or Current?
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In a transmitter with a capacitively coupled output, a change in instantaneous voltage created at the transmitter causes current to accelerate up the feedline (if the impedance is less than infinite). ...

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At near-QRP levels should I include a balun/unun in the antenna system?
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It depends. A choke and/or transformer between the feedline and the antenna changes the ratio of currents flowing on each, and thus where the EM radiation and thermal losses occurs. In some ...

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Ground plane reflects RF or brings it to ground
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The actual antenna is always balanced (as there are no magnetic monopoles in nature at any frequency, including RF). However, the actual antenna may include stuff that most people do not normally ...

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Is a resonant antenna inherently more efficient because it couples to free space more efficiently?
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Effective coupling can result in either higher gain (into some feed point impedance) or to higher heating losses (due to the antenna's elements own real impedance == resistance). Either way, energy ...

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Receiving range of ham radio on SSB with a portable radio reciever
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The range of amateur radio SSB over HF "shortwave" can be between a few meters to over 20000 kilometers, depending on frequency band, transmit power, antenna type/height/polarization/aim, ...

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How does IQ modulation work (intuitively)?
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As to the Hilbert transform for Rx or Tx? If you have a strictly real signal X (you calling CQ into a mic, etc.), it has conjugate symmetric sidebands, which is necessary for all the imaginary stuff ...

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What is antenna reactance?
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Any physical object where there are potential voltage or current reflections off of impedance mismatches or open circuits (such as the ends of a wire antenna) can change the AC waveform of the current ...

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what am i listening to when i listen to morse code?
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There are several methods to allow hearing CW as a audible sidetone on receive. Regenerative and direct conversion receivers often use the same method as they use for LSB/SSB receive and tune above ...

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How do I find when my license expires?
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The expiration date may be on the paper copy of your license. If you lost your paper copy, you simply can do a Google search (or other search engine search) for your callsign + "FCC". For a ...

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Does 3 W vs 5 W TX power make a huge difference in QRP CW operation?
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You can test the value of this difference. Emit a WSPR beacon, vary every other one in transmit power by 2.2 dB, and gather statistics over multiple cycles of the number of spots at each power level. ...

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Do chokes at the antenna feedpoint stop the coax from receiving signals as well, or just transmitting?
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A common mode choke at the antenna feedpoint will have little to no affect on whether received RF induces signals on the outside shield of a long (relative to the wavelength) coax. If you disconnect ...

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Is there an FT8 or other weak-signal digital mode specification available?
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To answer my own question: An article titled "The FT4 and FT8 Communications Protocols", by S. Franke K9AN, B. Sommerville G4WJS, and J. Taylor K1JT, in the July/August 2020 edition of QEX ...

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Can a receiving antenna really be "as small as you can imagine"?
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True only if you do not want to detect or receive the signal. Any physically realizable (e.g. made out of atoms) feedline, passive network, or receiver input connected to the antenna will add thermal ...

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What is minimum resolution for 2 frequencies to interfere each other
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If you want 2 unmodulated finite length sinusoids to be mathematically orthogonal, then the frequency separation is 1/T, where T is the length in time of a DFT used to detect them, and the period of ...

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Practicality of SDR-based TX/RX
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There are at least a couple differences that aren't just based on the specs (wattage, etc.) of current commercial offerings known to the OP. One advantage of SDRs is that some SDR setups (Hermes Lite ...

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Space Requirements
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Not much space at all is required for basic radio equipment. There are many handheld, portable, QRP, and kit radios that will easily fit in a small backpack or drawer. For HF antennas, big, outdoors,...

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Relation between antenna physical size and gain
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The angular resolution of an EM imager is in inverse proportion to its effective aperture. See Rayleigh criteria. A parabolic dish antenna can be thought of as an EM imager, similar to a radio ...

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Method to generate PIM
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Any non-linear device can work. But a good physical analog might be to find a crystal radio kit with a point contact crystal, and use the point contact detector inductively or capacitively coupled to ...

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What is IQ in the context of SDRs?
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IQ is a type of sampled data. Sampled data (a vector of numbers) allows digital processing (a bunch of arithmetic on finite size numbers), instead of using analog circuits (inductors, capacitors, etc....

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Why do we talk about common mode current from an antenna, but not from a transmitter?
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The outside shield of a coax can “radiate like crazy”, depending on the antenna and feedline configuration. This effect is sometimes noticed when shifting a feedline noticeably changes the SWR and/or ...

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Vertical antenna
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A single counterpose wire makes the antenna pattern directional, usually in the direction of the counterpose. Two or more counterposes in a symmetrical arrangement makes the antenna pattern more ...

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DIY SA612 + RTL-SDR HF receiver: good on laptop, but huge wideband noise on Raspberry Pi
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If the question is about how to solve this RFI/EMI issue, here's what I did to partially reduce the problem: I put chokes (multiple turns thru ferrite toroids) on every wire and cable connected to ...

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Batch sampling SDR
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The rtl_sdr command-line tool can capture a file of IQ samples of a specified (on the command line) duration, file name, center frequency, gain, and sampling bandwidth, from a connected RTL-SDR device....

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Tweak antenna resonant frequency higher
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If adding an inductive load half way up each leg of a dipole “lengthens” it, I might try the opposite to “shorten” it. Add a capacitive non-hat part way (half?) up each leg. This might partially ...

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Base vs center loading a vertical antenna
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As a rough rule of thumb, moving inductive loading from near the feed point to near halfway up an antenna of the same dimension might improve radiation resistance by somewhere around 2X, minus added ...

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Antenna testing, minimizing feed-line radiation?
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To add a partial answer to my own question, I realized I have at least one interesting test tool available, a tiny transmitter (TAPR WSPR board), controlled via a small computer (a Raspberry Pi Zero), ...

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Are transmit antennas the same as receive ones?
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There may be current carrying and legal requirements for transmit antennas (minimum 16 gauge wire size, insulators, separation distance from human bodies and heads, etc.) that do not apply to receive ...

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Weird Harmonic Issue on Raspberry PI FM Transmitter
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Connecting an antenna to a Raspberry Pi GPIO (usually 4 or 18) clocked at HF/VHF rates without a low-pass filter (and band-pass filter for higher frequencies) is a bad idea. This filtering is ...

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Key CW on zero crossings - zero bandwidth?
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From a mathematical point of view, any finite length (e.g. keyed) signal has infinite bandwidth. You can reduce the side-bands by choosing a keying envelope whose FT has low sidebands, which implies ...

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