hotpaw2
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Why do operators mention the band when calling CQ on phone?
15 votes

I have a scanner capable of HF receive, multiple HF receivers, and several HF SDR transceivers capable of receiving on more than one amateur band slice simultaneously. Lots of contest stations run ...

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Why is 20m band waterfall showing signals every 50 kHz?
13 votes

Those equally spaced lines in the waterfall are very likely from EMI/RFI noise generated by modern electronics, often harmonics and/or intermodulation coming from DC-to-DC power converters. Could be ...

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What is the decimal in Morse Code?
Accepted answer
10 votes

In the International Code of Signals (an International system of maritime communication, including radiotelegraphy), AAA (over-bar) is designated for both full stop and for decimal point. (See ...

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Why is Morse code still in use?
9 votes

Morse code requires an extremely small bandwidth (and is usable in a channel that has a relatively low S/N) for a mode that requires no digital processing hardware or computer/digital logic chips (...

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Is it legal to transmit with HackRF one?
7 votes

As for other legal alternatives, one might be transmitting inside a suitably shielded Faraday cage. I’ve seen such facilities at labs where various prototype and pre-production (and competitors?) ...

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Why were "PARIS" and "CODEX" considered "typical words"?
Accepted answer
6 votes

Answering the 2nd part: There seem to be many research articles and business documents reporting statistics on average word lengths, in characters, which seem to vary with language, dialect, corpus, ...

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Why are many ground radials preferable to a single ground stake buried 1m deep?
6 votes

The purpose of the ground radials isn’t to ground the counterpoise. The purpose of a dense field of radials is to emulate as much as possible a perfect mirror surface, so that, to the far field, the ...

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Why can't we use a simple wire for receiving 2.4 GHz signals?
Accepted answer
6 votes

A wire will pick up a GHz signal, as well as a ton of other RF signals, all mixed together. Some sort of filtering is required to separate out your desired radio signals. An Arduino has none of ...

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Vertical Yagi spun at 1000 RPM: gain properties?
6 votes

Depending on the gain characteristics of your Yagi antenna, you’ll be adding an amplitude modulation of 16.7 or 33.3 Hz to your signal, plus a similar phase modulation. These added modulation ...

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Calculation of transceiver current draw
Accepted answer
6 votes

The rest (of the current) is why your transmitter requires heat sinks (and/or airflow for thermal dissipation). Linear amplifiers are usually not anywhere close to 100% efficient. A high SWR might ...

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Why is gain used?
6 votes

The directional antenna doesn't actually radiate 200 Watts, it just focuses the actual mere 100 Watts so that along some optimal directional axis, a receiver would see same power as if an imaginary ...

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Common-mode choke (CMC) hurting my SWR. Live with it? Drop the choke?
5 votes

A choked end-fed antenna is (or acts just like) a highly off-center fed dipole, where the length of any stub between the common mode choke and the unun/transformer/feedpoint sets the off center ratio ...

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Is the Boom Strictly Necessary in a Vertical Dipole?
5 votes

If you don't route the feed line away from a center-fed dipole antenna at 90 degrees, it will be in an unbalanced RF field, and thus will couple to the unbalanced RF field, to some degree, even with a ...

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Is a magnetic loop antenna a good option for those in an apartment?
5 votes

In, meaning Inside an apartment, a magnetic loop may not be a good idea for transmit, as the RF magnetic field can couple very strongly to any household wiring or appliances inside, window frames, etc....

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Will using a 1:1 balun at the feedpoint of a center feed dipole result in no common mode current on the outside of the coax?
Accepted answer
5 votes

Depends on how much current you mean by no current. But in general, unless the dipole is actually perfectly symmetrical, in a perfectly symmetric environment, above a symmetric ground, with the ...

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How to get professional or official clarification of FCC Part 97 rules for specific complicated situations?
5 votes

The ARRL itself is not a law firm, but might be able to refer you to an attorney or lawyer with experience in federal communications law and FCC regulations who can appropriately advise you, and even ...

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Is it legal to broadcast an FM radio signal with a Raspberry Pi Zero?
5 votes

When running rpitx or pifm on a Raspbery Pi, the "transmitter" output uses an unfiltered digital I/O pin. Thus you not only need to worry about FM band interference, but emission laws and ...

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How does selecting the opposite sideband when receiving CW on HF reduce interference?
5 votes

If you are using (or building) a vintage radio that does not have a narrow CW audio filter, the audio bandwidth above and below a listenable CW audio side-tone frequency can be quite unsymmetric. By ...

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Is copper-clad steel a good material for wire antennas?
5 votes

Depending on the RF frequency and wire diameter, skin effect may dominate the effective resistance at that frequency. If so, since copper has a lower resistance, any resistive losses of a copper skin ...

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What is a "dip relay" and how does one use it to build a transmitter?
5 votes

This design could be using the key to control a tiny relay (possibly inside a Dual Inline Package) to connect and disconnect a tiny low power oscillator from the antenna feed.

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What safety procedures should be followed when developing and testing a high power amp?
4 votes

If you do have to stick a scope probe or adjustment tool into it, take off all your rings, watches, bracelets, necklaces, etc., before reaching into anything (or around any uncovered circuitry) that ...

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What cause the spectrum peak of `center frequency`?
4 votes

In addition to the clock leakage mentioned in the other answer, a DC offset spike can also show up in the downmixed IQ if the mixer(s) and/or the ADC(s) aren’t perfectly balanced (exactly equal gains ...

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

If you use SDRSharp with an Airspy Mini, instead of an RTL-SDR, the supported sample rates allow up to 6 MHz bandwidth, due to the use of an ADC with a higher sample rate than the RTL2832 is capable ...

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Tuner at antenna side versus transmitter?
4 votes

I'll add that a tuner is used for tuning, and tuning, for a single or small set of frequencies is often done at the antenna, usually by adding or adjusting a loading coil or adding a capacitive top-...

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What's the realistic SSB reception range for 25W on 20m and 40m?
4 votes

Depends on ionospheric propagation conditions (sun spots, solar flux index, time-of-day, direction, and etc.). People have completed QSOs at well over a thousand miles with a few milliwatts in CW. A ...

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What type of antenna are these?
4 votes

Looks like a vertical array of circular polarized antennas, each half element as half turnstile and half traveling wave used for the circular phasing.

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what is main reason for formation of side lobes in directional antennas?
Accepted answer
4 votes

Similar to optics or a water tank, waves passing through a finite aperture will produce a diffraction pattern. To over-simplify: In the far field, the difference between the distance to the left and ...

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What limits a PIN diode or varicap from being used in a "Software Defined [Radio] Filter"?
4 votes

Another difference between using a varicap for oscillators versus for input filters is feedback. You can feed the output of a variable oscillator into a phase comparator or frequency counter to ...

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Can I learn cw at too high wpm? Should I slow it down?
4 votes

If you want to actually successfully operate, then you should (eventually) practice copying Morse Code at the full range of WPM speeds you expect to hear over the air. Most Morse Code practice ...

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Problem with sample rate
4 votes

The RTL-SDR interfaces to your computer via USB. The USB interface and driver will buffer the data and send it to your software at the requested sample rate on average (baring underflow due to ...

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