hotpaw2
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Eliminating RFI from raspberry pi
1 votes

If the suspected RFI is conducted from the Pi, then the RFI spectrum should change if you use a much longer USB cable with both ends of the cable wrapped several turns through large enough ferrite ...

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Is there value in grounding the virtual null in an auto transformer?
Accepted answer
3 votes

An end-fed acts more like a highly off-center fed dipole. Thus, the point you label "GND" is really the attachment point to the the remaining portion of the dipole, either something like a 5%...

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How to transmit computer audio to a wireless microphone receiver?
1 votes

An educational SDR kit, such as the ADI ADALM-Pluto or a Lime SDR Mini, can be used as a UHF exciter, with any modulation that your receiver requires generated by software synthesis (GNU radio , et. ...

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What's the difference between LPF and BPF in context of bandwidth setting?
3 votes

The 300 650 combination is often used for CW (Morse Code) reception. It tunes the SDR receiver’s (Tayloe mixer or FPGA or software synthesized) oscillator(s) 650 Hz below (or above for LSB) the dial ...

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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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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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Learning morse, but I can't write fast enough?
3 votes

The Unix diff utility can handle out of sequence misses. My morse code software offers to display (or hide) the complete text (of its randomly selected words or code groups it plays as audio Morse ...

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Is it necessary to have a "loop" antenna to make the primary antenna work?
2 votes

It is most commonly unnecessary to need a loop antenna to make a (tall) vertical antenna work. However, a horizontal loop antenna has a different polarization (like polaroid sunglasses for reflections)...

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Antenna tuner at the transceiver output confusion
1 votes

Lets simplify the scenario a little by using a resistor at the end of a 50 foot long 50 Ohm impedance feedline instead of an antenna. If the resistor is zero Ohms, then about 100 nS after enabling a ...

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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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EIRP - Conservation of energy
3 votes

That’s just conservation of energy. In the one dimensional case, 100 mW would “isotropically” radiate 50 mW backwards and 50 mW forwards. A one dimensional 3 dB directional gain would just move that ...

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What cause the shape of frequency spectrum convex or concave?
0 votes

Answer to part 2: The USRP SDR uses an downconverting IQ modulator before the ADCs. An error in quadrature phase or quadrature levels of the two IQ modulator clock signals or gain and delay balance ...

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What is the minimum height required for a 60 meter NVIS antenna?
0 votes

One of the comments for this question includes a link to a paper on blast-resistant ground level HF antenna's that the U.S. Airforce used or uses. So zero. Or negative if you count the buried cavity....

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Audio frequency used for Morse code in licensing exams?
1 votes

I found a comment on the web that the U.S. Army used 641 Hz for their radio operator Morse Code training.

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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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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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Does an SWR higher than 1:1 necessarily cause additional heat in the transmitter?
1 votes

As an additional answer, I would add that the answer most appropriate for many operators is to test this with their actual transmitters. For equipment safety, one should test this by transmitting at ...

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What is a "direct sampling superheterodyne" receiver?
1 votes

The 7300 is a direct sampling receiver, since it samples RF at well above twice the the band frequency of interest. However, there is more than one signal path with more than one bandwidth and center ...

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Does an SWR higher than 1:1 necessarily cause additional heat in the transmitter?
1 votes

If a load is reactive (inductive or capacitive) then sinusoidal voltage and current feeding that load will be out of phase. Therefore, to output the same power (to be dissipated by the load as heat ...

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How much is the greatest distance of a communication link that man can reach? Intergalactic? (ascertainable)
Accepted answer
1 votes

The latest distance estimates for the Voyager spacecraft transmitters is displayed on a NASA web site, as well as the last communication date. AFAIK, there is no, more distant, humanly accessible and ...

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Is this true about ferrite loop antennas?
2 votes

Nearby antenna elements do affect each other. Consider a Yagi-Uda. Pointed in the "wrong" direction, the director and reflector elements will reduce the EM power that the driven element ...

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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's the `Minimum signal duration` and `Minimum detectable signal duraion` of Ettus B210?
0 votes

The bandwidth and thus the impulse response duration of any anti-aliasing filter(s) in front of the ADC affects the minimum duration of a signal that can pass the input filter(s) without (more than ...

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Does signal frequency affect the band width of SDR hardware?
1 votes

In SDR receivers which use a mixer in front of the ADC to receive radio spectrum above the ADC sample rate(s), the sample rates and down-conversion frequency are usually independent settable (except ...

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How did "rational resample" change the type of wave?
1 votes

A (non-undersampling) resampler usually assumes that the total signal represented by the original samples is baseband bandlimited (perfectly low-pass filtered), and thus contains no frequency spectrum ...

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What cause `multiply` has difference result between `float` and `complex` signal?
1 votes

A real-valued multiply is the same as an AM modulation, where the result includes both upper and lower sidebands. (Similar to the spectrum of an AM radio station on an SDR waterfall.) A complex-...

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Why does a sine wave show two peaks in the frequency domain on GNUradio?
0 votes

The output of the FFT you used is complex. When you input a strictly real signal to a FFT that produces a complex result, half of the complex result is the complex conjugate of the other half (this ...

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Broadband dipole with no standing waves?
Accepted answer
1 votes

Any change in impedance at the end of a wire, different from the rest of a transmission-line-like wire, will reflect some current. An impedance matched resistor at the ends of a dipole won't reflect a ...

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Why does a channel get transmitted for a wide frequency range at night in Amplitude Modulation?
Accepted answer
1 votes

It's possible that your AM radio has a very wide bandwidth (low Q filters), so high power broadcast stations far from the center tuned frequency can be heard, but are drowned out by higher RF noise ...

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