# Tag Info

9

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 WWV, but they have modulated time information in addition to the carrier which serves as a frequency reference signal. What you are receiving is almost certainly ...

7

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 factor $F$ is the linear ratio form of the noise figure which is given in decibels. For example, the first component may be an LNA, the second component a ...

7

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 atmospheric noise is high. On VHF and UHF the natural noise floor is lower, and low-noise receivers are more expensive, so it is possible but not guaranteed. It will ...

7

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 just amplifying inputs, they also mix them to some extent. So any input to the receiver which contains more than just a single frequency will generate some ...

6

I have read this too. I don't have personal data to back this up, but the reasoning I have read stated that local RFI (like household appliances) tended to be vertically polarized and hence more able to induce noise onto a vertical antenna than a horizontal one. I'll edit the answer when I find the references. Meanwhile there are a few really excellent ...

6

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. Make sure any battery powered computers/tablets are fully powered off. If the noise reduces, turn off all branch breakers, turn the main breaker back on, and ...

6

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 noise resistance also an inherent property of FM? Huh, that surprisingly can be a pretty philosophical question about what bandwidth actually is, but let's ...

6

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 the electric field strength to the magnetic field strength is called the field impedance. For any antenna, several wavelengths away (in the far field), this ...

5

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, through subtraction of an estimate of the average noise spectrum from the noisy signal spectrum. The noise spectrum is estimated, and updated, from the periods ...

4

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: what does the RS-232 standard say or what does your RS-232 chipset and UART require? I have formulated my answer from the perspective of the former. RS-232 ...

4

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 receive. Some other troubleshooting ideas: Check your radio's power supply for noise by substituting a battery and disconnecting the PS from the wall. Run ...

4

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 on 10m. In investigating this, I tried running my radio (IC-718 with a 40m cut OCF dipole, mildly sloping wires, peak at about 25 feet, directly over the house)...

4

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 ratio. In simple cases, this might simply mean reducing the bandwidth of an analog receiver. Sure, voice will not sound as crisp, but if that buys one a ...

3

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 company almost 90 days to fix it, but went from +20 static down to S-2 or 3. Also using a 160-10 fan dipole here. The problem insulator was at least 100 yards ...

3

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 like "pink noise" would be inaccurate. For example, lightning is a significant contributor to noise on HF, and it comes in "crashes" as you might expect. There ...

3

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 approximately equal to the wavelength, are more like folded dipoles and behave differently. Is a loop antenna better than a whip when man made noise in the near field ...

3

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 radiation outside the designated channel. But every radio does that. Modern cell phones also dynamically adjust their antennas so they are more sensitive in the ...

3

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. Absolutely no contest. The vertically-polarized antennas transmit DX very well, however. I actually run two antennas -- horizontal for listening, and transmit. ...

3

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 individual molecule is taking a random path all over, colliding with the walls of the room and other molecules. The only way to get rid of this random motion of ...

3

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 effectively a vertical with no radials. This means much of the ground current is in the soil. The soil is a resistor. Resistors convert electrical energy into heat. ...

3

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 less likely to be identified as a newbie. But we have all gone through this phase so I can assure you that once you get a few QSOs under your belt, you will be ...

3

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 with DC-DC converters can still produce, perhaps radiate, RF noise. The solar panels might have DC-DC converters that can't be switched off. Try throwing a ...

3

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 mix of digital and analog FM, depending on what the other station is transmitting. If you can find information on the repeater, you will probably discover what ...

3

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, it could be related to a lighting device such as a mercury vapor lamp, an LED light, holiday decorations or similar. It could also be some type of industrial ...

3

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 primary ways of reducing the received noise. On a small lot, this is not always possible but improvements should at least be evaluated. For example, an ...

2

I am a complete novice, so it does not necessarily mean that what I found on is something I understand, especially in terms of application to amateur radio - I would like to figure out how to apply some of the reduction techniques: From a set of lecture notes from a college class: "Thermal noise is produced by the motion of free electrons in a resistance ...

2

It's very difficult to say. Factors like ambient man-made noise around you can vary by orders of magnitude based on your location. Likewise, your radio system's internal noise and ability to reject ambient noise can vary by orders of magnitude. The difference between a \$20 RTL-SDR dongle in an urban environment and a \$2,000,000,000 array of receivers ...

2

It's expected that the total noise temperature to vary with elevation. Three major effects to consider: Sidelobe pickup of noise from the ground, this is the dominant effect Variation of atmospheric loss at different elevations, not really relevant for UHF frequencies The sky temperature itself, which varies mainly depending on whether you're on or off the ...

2

I've seen similar 'roving' signals emanating from low quality switching type power supplies, which can generate noise at multiple harmonically related frequencies. Since you've mostly ruled out local sources, you might have to do a bit of sleuthing with a small directional loop antenna and a portable receiver. A cheap RTL type SDR receiver with a down-...

2

I applaud you for wanting to learn how to potentially improve your AIS station. As others have commented, your questions can yield a response the size of a textbook but here are a few pointers to get you started. Perhaps some experimenting will lead you to post further questions for this forum which will help others with their understanding as well. You ...

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