17 votes

What is the difference between channel & frequency & band in RF?

If you don't know what a frequency is, you need to read up on waves-in-general and radio waves. But the other two terms can be defined in terms of frequency; frequencies are the “natural” thing and ...
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  • 22.9k
14 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 ...
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13 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 ...
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  • 22.9k
13 votes
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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. ...
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  • 7,817
12 votes
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How can you calculate the frequencies for each band?

$$ \frac{c}{ \text{frequency}} = \text{wavelength}$$ $$ \frac{c}{ \text{wavelength}} = \text{frequency}$$ The above relation is a fact of physics. It's true unconditionally (provided you are using ...
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  • 22.9k
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 ...
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9 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. ...
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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 ...
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9 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. ...
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  • 7,817
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 ...
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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 ...
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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 ...
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  • 7,495
7 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 ...
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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 ...
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  • 22.9k
7 votes

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 ...
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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 ...
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7 votes
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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: $...
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7 votes
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Why is there a repeater on 146.46? Isn't that a simplex frequency?

Per the ARRL: A band plan refers to a voluntary division of a band to avoid interference between incompatible modes. The regulatory bodies for other countries have similar declarations for their ...
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  • 1,212
6 votes
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Antenna size for wideband

An antenna of the wrong size is just an antenna that is not resonant at the particular frequency — meaning that each cycle of the radio wave captured by and conducted in the antenna does not perfectly ...
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  • 22.9k
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 ...
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  • 22.9k
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 ...
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  • 18.1k
6 votes
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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 ...
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  • 18.1k
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 ...
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6 votes
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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 ...
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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, ...
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  • 1,615
6 votes
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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 ...
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6 votes

What frequencies in 118–173 MHz can I transmit on without a license in Canada?

None. Basically, aside from a few ISM bands, none of which are covered by your radio, you can transmit nowhere without a license, unless you're using hardware that restricts you to legal usage (e.g. ...
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6 votes
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Electromagnetic signal from spark gap

Don't worry, there have been many researchers before you, and you can borrow some of their work. Your English is fine. If you do a web search for "lightning spectrum", you will find a ...
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  • 8,922
5 votes

How can you calculate the frequencies for each band?

The names make a kind of sense if you take into account the history behind them. Look at this pattern of names and lower end of the allocation: 80m: 3.5MHz 40m: 7.0MHz 20m: 14MHz 10m: 28MHz Note how ...
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5 votes

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

Yes & No. The Baofeng is capable of transmitting on FRS/GMRS & MURS. But its not legal to do so (except maybe on GMRS with a license). And no frequency is "secure" as in "private" with any ...
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