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13 votes
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What are these continuous sine wave tones I keep hearing?

A pure tone is an unmodulated signal — it carries no data. Almost nobody intentionally transmits a pure tone — it would be wasteful. The exceptions are the time-and-frequency reference signals like ...
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12 votes
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How can I calculate the effects of an LNA, antenna gain, etc. on noise performance?

Try the Friis noise formula: $$ F_{eq} = F_1 + {F_2-1 \over G_1} + {F_3-1 \over G_1 G_2} + \cdots \tag 1 $$ $F_n$ is the noise factor of the n-th component, and likewise $G_n$ is the gain. The noise ...
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11 votes
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How does lowering the RF Gain help with SNR?

For an ideal, linear receiver, reducing the RF gain by 1 dB lowers signal and noise by 1 dB, so there would be no change in SNR. However, receivers are not perfectly linear. This means that besides ...
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7 votes
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Can I improve reception with a more sensitive antenna / preamplifier / better feedline?

These things will significantly help under one condition: the RF noise floor is below the receiver's noise floor. This is almost never the case on HF, where low-noise amplifiers are easy and ...
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6 votes
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HF Noise Level S5 to S9+18

Some troubleshooting ideas: Check your radio's power supply for noise by substituting a battery and disconnecting the PS from the wall. Run your receiver on a battery and turn off your main breaker. ...
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6 votes

Is FM modulation still more resistant to noise when given the same bandwidth as an AM signal?

FM modulated radio is much more resistant to noise and can deliver better sound quality than AM radio. Under certain conditions, that is! Namely, additive noise, and a fading channel. or is this ...
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6 votes
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Does a loop antenna have less susceptibility to atmospheric noise than an open ended antenna?

Your reasoning is not too far off. Say you attach a signal generator to an antenna, and then probe the magnetic and electric fields at many places around this antenna in a test chamber. The ratio of ...
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5 votes
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Noise & shielding, SDR Dongle

While the other answer is quite detailed, this one is much shorter and specific: I purchased and installed an aluminum RF shield for the dongle. The noise floor is significantly lower as a result! ...
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  • 789
5 votes

Noise & shielding, SDR Dongle

“Sensitivity” isn't all that well-defined. Insofar as it is, you might as well just think in terms of noise, because there is always a noise floor and it's always what determines the weakest signal ...
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  • 22.9k
5 votes

What is Spectral Subtraction for noise reduction?

From https://link.springer.com/chapter/10.1007/978-3-322-92773-6_9 : Spectral subtraction is a method for restoration of the power or the magnitude spectrum of a signal observed in additive noise, ...
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  • 7,495
5 votes
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How to track down and neutralize this apparent mixer creating noisy emissions around my signal?

This is caused by the RTL-SDR I was using to view my signal. Here's a quote from the guide at https://www.rtl-sdr.com/rtl-sdr-blog-v-3-dongles-user-guide/: Note that this feature makes use of direct ...
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  • 191
4 votes

Is a vertical noisier than a dipole, and if so, why?

I live in Seoul, Korea, a city of 15 million, with lots of lights and electronics on late until 11pm. My vertical dipoles I have created are easily 1 to 3 s-units noisier than horizontal dipoles. ...
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4 votes

Baud rate/frequency/bandwith/characters per second

The issue of filtering RS-232 (or any slow digital signal) is not so much the baud rate as it is the required rise and fall time of each bit. There are two ways to quantify this rise/fall time issue: ...
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4 votes
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Is 20m noisy, or do I have a lot of local interference?

Make certain you have a 1:1 choking balun at the apex of your antenna. This will reduce or eliminate the possibilty of common mode currents on your feedline causing it to pickup local interference on ...
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  • 18.1k
4 votes

Is 20m noisy, or do I have a lot of local interference?

At my home, background noise is typically S6-S9 pretty much all the time on anything lower than 20 meters. 17 and up is generally less noisy, although I occasionally will have some really strong noise ...
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4 votes

What does a receiver's noise reduction function do?

What does this noise reduction do? That should depend on the device. Generally, it's to be assumed that it applies (analog and/or digital) signal processing to improve the perceived Signal-to-Noise ...
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4 votes
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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?

Receive power does vary with SWR; but for reception quality we're interested in signal-to-noise ratio. As long as you're getting enough receive power that the noise received from the antenna is ...
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  • 8,833
4 votes
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Why is QRN so bad on the low HF and MF bands?

The primary source of atmospheric radio noise is the estimated 40 lightning strikes that occur each second around the world. NASA's Review of Measurements of the RF Spectrum of Radiation from ...
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  • 7,685
4 votes

QRN: How to chase down a solid S9 noise floor on 40m only

Look around your neighbourhood or Google satellite imagery for new solar panel installations. We recently discovered a solar panel installation with noisy regulators creating noise at a neighbours ...
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3 votes

HF Noise Level S5 to S9+18

Just went through the same thing last year. One hint - does the static level lower when it rains? if the answer is yes, very likely a bad insulator or distribution transformer. Took my electric ...
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  • 81
3 votes

Loop Vs Whip for MW DX

I'm going to assume that by "loop" you mean a "magnetic loop" or a "small loop". That is, one with a circumference significantly less than the wavelength. Larger loops, with a circumference ...
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3 votes
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Cell Phone Filter / Interference?

How do cell phone filters filter out all the extraneous EM waves and noise (especially noise) when you get a call? Short answer: they don't. Of course, they use a bandpass filter to reject EM ...
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3 votes

Color of radio noise?

There is no single answer to your question. Atmospheric noise varies over the RF spectrum. It's generally true that the natural RF noise power is higher at lower frequencies, but to call it something ...
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3 votes
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Inquiry regarding thermal resistor noise

Imagine an ordinary gas, like air, inside a room. If the room is perfectly sealed and the air is completely still, we can say that the average motion of all the gas molecules is zero. However, each ...
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3 votes

Signal path to maximize RFI rejection in an urban environment

Definitely do: Counterpoise in addition or in replacement to ground connection Roof mounted antenna Or generally, some improvement to the antenna. Your existing antenna sounds like ...
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3 votes

Signal path to maximize RFI rejection in an urban environment

As a new ham, you may have more success answering a CQ since you will then know that you can at least hear the other station over your local noise. Answering a CQ also requires less finesse so you are ...
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  • 18.1k
3 votes

What can I do about my strong RF noise?

You killed the main AC circuit breaker to your house, but still detect RF noise centered at your house? Battery operated devices (laptop?, electric car?), systems with battery backup, and batteries ...
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  • 12.4k
3 votes
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How do I have a full signal of noise on a handheld?

That's not noise, it's digital voice. DMR, DSTAR, and P25 are digital modes that find popular use on the amateur bands. Some repeaters are digital-only. Others are dual-mode, so you will encounter a ...
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3 votes

High Noise Floor on 40/80m at Night

I'm unsure if it's something in my area or something to do with my equipment? Since the effect is time dependent, it is most likely RFI caused by a timed electrical device. Based on the time of day, ...
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  • 18.1k
3 votes

Doublet with ladder line vs coax w.r.t. noise

There are a few things to think about. Coaxial cable will likely not have a positive impact on your RFI. Unfortunately, urban locations are loaded with RFI. Antenna direction and distance are the ...
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  • 18.1k

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