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15 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 ...
Kevin Reid AG6YO's user avatar
  • 24.7k
15 votes

Why are radio frequency ranges aligned on multiples of 3?

The ITU bands are actually delineated along plain powers of ten! They're just hiding a bit. From the description above a table of all the bands on Wikipedia: As a matter of convention, the ITU ...
natevw - AF7TB's user avatar
12 votes
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What is a "calling frequency"?

A calling frequency is a common channel known to all - this is the channel that anyone can jump onto and say Hi! Or a specific person you know may be monitoring this channel, you can call out to them. ...
Matt Clark's user avatar
12 votes
Accepted

Why is 9 kHz the lowest frequency for spectrum analyzers?

Spectrum analysers are often specified down to 9 kHz because this is the lowest frequency of conducted or radiated emissions that is specified in the Electromagnetic Compatibility (EMC) standards. ...
tomnexus's user avatar
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11 votes
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What is inside a 50 ohm termination?

It depends on the frequency range the termination is rated for, and the power handling required. High power and high frequency is very difficult. At HF, any old non-inductive 50 Ω resistor will do. ...
tomnexus's user avatar
  • 11.4k
11 votes

What is the frequency range 2300-21950 kHz used for?

"Shortwave" means roughly the same thing as "HF": 3 to 30 MHz. It definitely does not include the FM broadcast (around 90 MHz, too high) or AM broadcast (around 1 MHz, too low) bands received by a ...
Phil Frost - W8II's user avatar
11 votes
Accepted

How is FT8 modulated with both upper side band and FSK?

Remember that, theoretically speaking, a USB transmitter just takes a signal, shifts it up in frequency, and amplifies it. That means that if you take a 50Hz wide 8FSK signal centered at 1500 Hz, and ...
hobbs - KC2G's user avatar
  • 12.5k
9 votes

Can my laptop pick up CB radio frequencies?

Yes, very strong radio signals can be picked up by just about any device with a speaker and a transistor in it. The transistor acts as a rectifier, forming a crude envelope detector. Amplitude ...
Phil Frost - W8II's user avatar
9 votes
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How does a receiver know the exact frequency in the channel to "listen to"?

The signal is not at exactly one frequency. The only signal that exists exactly at one frequency is an unmodulated carrier, and such a signal contains no information. As soon as the carrier is ...
Phil Frost - W8II's user avatar
8 votes
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Why do the ham radio bands get broader with increasing frequency?

There's more space at higher frequencies so the allocations can be bigger. Consider the difference between 15 MHz and 30 MHz, and the difference between 5,015 MHz and 5,030 MHz. It's a 15 MHz change ...
Phil Frost - W8II's user avatar
8 votes
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What do old unit abbreviations like "mfd" and "kc" mean, and where did they come from?

These were common abbreviations in use for Components, Radio equipment, and Printed publications in the 19th and most of the 20th century. Mfd = microfarad or μF kc = kilocycles or kHz. 1,000 cycles ...
Mike Waters's user avatar
  • 8,071
8 votes

How is FT8 modulated with both upper side band and FSK?

FT8 is just FSK. However, most legacy transceivers don't support direct digital to FSK modulation (and FSK to digital), but do support SSB modulation and demodulation (from and to audio). So these ...
hotpaw2's user avatar
  • 13.5k
7 votes

Why do the ham radio bands get broader with increasing frequency?

There are some straightforward reasons I can think of which apply to all spectrum allocations, not just amateur radio: In a lot of cases, the bandwidth of a RF device is relative; if you are using ...
Kevin Reid AG6YO's user avatar
  • 24.7k
7 votes
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What is the best frequency to start working EME on a budget?

You're generally right, the free space path loss formula incorporates wavelength quadratically, so it would seem wise use the lowest available frequency. Since you're bouncing off an object, you get a ...
Marcus Müller's user avatar
7 votes

Output power from the TX/RX port of the USRP N210 decreases as the frequency increases

That's an expected phenomenon: Real-world physical systems tend to be frequency-selective (i.e. not constant over frequency), and "at large scale" low-pass systems. This applies to ...
Marcus Müller's user avatar
7 votes
Accepted

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

Because mathematically, a function like $\sin(\omega t)$ has an angular frequency of $\omega$ and $-\omega$. Consider: $$ e^{i\omega t} + e^{-i\omega t} $$ By Euler's formula this can be expanded to: $...
Phil Frost - W8II's user avatar
7 votes

What cause the spectrum peak of `center frequency`?

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 ...
hotpaw2's user avatar
  • 13.5k
6 votes

Can a Baofeng UV-5R+ be used on FRS, GMRS, and MURS?

Legality is a big issue. Not to be ignored. There is no legal way for you to do as you suggest in the USA. This radio is too powerful to be legal on FRS. You need a license for GMRS. Applications ...
SDsolar's user avatar
  • 2,089
6 votes

Why do Hams refer to bands by wavelength and not frequency?

I'd agree with @user3486184's answer, that this is primarily an effect of tradition. However, what @DaveTweed answered hit the spot how that tradition came to be: In early radios, you really had not ...
Marcus Müller's user avatar
6 votes

What is a "calling frequency"?

Calling frequencies are defined for specific bands and most common for VHF and UHF and are mode specific (i.e. Weak signal, FM simplex, etc.). In fact, knowing calling frequencies such as 2-meter ...
K7PEH's user avatar
  • 3,008
6 votes

Does antenna frequency matter when trying to pick up radio waves?

You can think of the frequency range specification as if you did have an ideal “every frequency” antenna but the signal passes through a filter before reaching the receiver. That is, any signal will ...
Kevin Reid AG6YO's user avatar
  • 24.7k
6 votes

Private Channel?

There is a way to use radio waves to hold a private conversation. It's called a mobile telephone, and they are available with surprisingly good coverage around the world. We should always use a tool ...
Scott Earle's user avatar
  • 4,619
6 votes

Radio Range vs. Frequency

This is an interesting question and while we may not be able to get to an exact answer, we can certainly explore the issues to consider. First we start by calculating a primitive link budget. The ...
Glenn W9IQ's user avatar
  • 18.6k
6 votes
Accepted

What are Radio-location Services in the 1.9-2.0 MHz range?

I wish you well with the general test! The radiolocation services in question are defined in CFR 47 §2.106: NG92 The band 1900-2000 kHz is also allocated on a primary basis to the maritime ...
Glenn W9IQ's user avatar
  • 18.6k
6 votes

What are these antennas used for?

UPDATE: I've started a followup question regarding the leftmost antenna, which I originally took to be a discone. See: What sort of antenna would use a bicone or lozenge-like arrangement of vertical ...
natevw - AF7TB's user avatar
6 votes
Accepted

Why do receiver sensitivities vary so much with frequency?

Detecting a signal is not a question of amplifying the signal: the problem is distinguishing the signal from the noise. Noise by nature is random: individual observations are unpredictable, but as ...
Phil Frost - W8II's user avatar
6 votes

How does a receiver know the exact frequency in the channel to "listen to"?

It may be easier to think of the receiver as receiving all frequencies. The job of the receiver is not to tune to a single frequency. Its job is to filter out everything that's not at that frequency, ...
user3486184's user avatar
  • 1,957
6 votes

GnuRadio RF transmission, legal and safety issues

The frequency allocation chart is really more artistic than informative. You can not and should not use that as a guide for selecting a frequency. There is too much information to fit on the chart, ...
user10489's user avatar
  • 6,485
6 votes
Accepted

Locate a ball 1000 times a second

I want to locate a small ball in the air 1000 times a second. The ball is thrown from the ground and then flies in the air for 0.5 seconds until it lands. Distance from the location instrument is 1 ...
Marcus Müller's user avatar

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