14
votes
Accepted
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 ...
- 51.6k
14
votes
Accepted
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 ...
- 24.4k
11
votes
Accepted
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 ...
- 51.6k
6
votes
Accepted
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. ...
- 18.5k
6
votes
Accepted
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 ...
- 15.5k
6
votes
Accepted
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 ...
- 51.6k
6
votes
Accepted
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 ...
- 11.7k
5
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. ...
- 59
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, ...
- 7,864
5
votes
Accepted
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 ...
- 191
5
votes
Accepted
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 ...
- 7,818
5
votes
Are there any modes that use pseudo-random noise codes to "amplify" signals?
If you're asking if Amateur Radio licensees use modes based on PRC, it may depend on how those are defined exactly. There are some relatively common ham radio modes that allow decoding near or below ...
- 7,269
5
votes
Accepted
Why are there weird sounds in radio?
What you describe is at least in part a feature of single side band demodulation. The radio is taking a range ("window" of bandwidth) of RF spectrum and shifting it to the audio spectrum. ...
- 5,651
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: ...
- 18.5k
4
votes
Accepted
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 ...
- 18.5k
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 ...
- 41
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 ...
- 15.5k
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 ...
4
votes
Accepted
Is the noisy spectrum from 20MHz to 330 MHz normal?
Is this expected?
This is actually better than many people would expect, yes, assuming the floor at ca -130 dBm/300 Hz ~= -153.5 dBm/Hz is mostly thermal noise + spectrum analyzer noise temperature.
...
- 15.5k
4
votes
Is the noisy spectrum from 20MHz to 330 MHz normal?
The 0-300 MHz spectrum is full of strong signals, but it should be at least half empty, meaning that in many places an instrument with excellent selectivity would not see anything above thermal/...
- 10.5k
4
votes
Accepted
Why does my received power rise so much when I connect an antenna?
I suspect the background noise is from your FPGA development board, coupled to the antenna via the cables. You should see plenty of signals in that band but there should also be places where you get ...
- 10.5k
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 ...
- 18.5k
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 ...
- 51.6k
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 ...
- 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 ...
- 51.6k
3
votes
Accepted
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 ...
- 51.6k
3
votes
Accepted
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 ...
- 51.6k
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 ...
- 13.2k
3
votes
Accepted
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 ...
- 51.6k
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, ...
- 18.5k
Only top scored, non community-wiki answers of a minimum length are eligible