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15 votes

How far do radio waves travel?

Radio waves don't stop at a distance, they just get weaker; you've read this correctly. The reason that communications stop working at some distance is that the signals are too weak to be understood. ...
Kevin Reid AG6YO's user avatar
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14 votes
Accepted

Non-traceable radio emitters

IMO, your question is too general to give a good, specific answer. Also, it would help if you elucidated the motivation for the question. I am a semi-retired electrical engineer, not a security or RF ...
Manfred VK3AES's user avatar
11 votes
Accepted

Using shortwave communication, how difficult is it to transmit messages from the UK to the US?

To send a message of around three bytes over such a long distance, would this require an antenna that uses a lot of power? No. There's a huge variety of tradeoffs here, but as a quick calibration, ...
hobbs - KC2G's user avatar
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11 votes
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How to determine frequency and launch angle given a target skip distance?

The actual math here is annoying enough that you will hardly ever want to use it (it requires knowing the incidence angle of the signal on the ionosphere, which is dependent on the height of the F-...
hobbs - KC2G's user avatar
  • 12.5k
11 votes

Non-traceable radio emitters

Another possibility to look into is meteor burst communication. This is a well-established technology. You beam a VHF signal up into the sky, it bounces off a meteor trail, and your recipient picks up ...
Martin Kochanski's user avatar
9 votes

Does geology affect radio signals?

Other Effects are there any other geological properties that can affect radio waves? Yes, there are other effects. Basically, every material affects the propagation of radio waves. Absorption That ...
Marcus Müller's user avatar
9 votes
Accepted

How can Ground Penetrating Radar work?

There is a special adaptation of the Friis equation, called the Radar Equation, that describes the range of a radar system. Here is a basic version that calculates the maximum range of a radar system: ...
Glenn W9IQ's user avatar
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9 votes

Communications : Ground wave propagation

So, I'll take this very smoothly. The idea is to take you from ray optics gradually to an understanding of radiomagnetic waves as actual waves, and show that it all makes sense. 1st idea: Refraction ...
Marcus Müller's user avatar
9 votes
Accepted

Do short waves pass through or reflect off concrete buildings?

The concrete is relatively transparent to radio waves of such large wavelengths (it attenuates, it doesn't reflect). However, steel bars within concrete typically convert that concrete to a solid ...
Marcus Müller's user avatar
8 votes

What's the difference between "maximum usable" and "critical" frequencies?

The maps are related, but as this excellent posting describes: The 'critical frequency' is the highest frequency that gets reflected when it is aimed straight up at the ionosphere. However: …...
natevw - AF7TB's user avatar
8 votes

Why is VHF better than UHF in this situation?

This is an ill-posed question, since "best" could mean so many things. If VHF is so plainly best, why does anyone bother with UHF at all? If you mean what option has a lower path loss, then sure VHF ...
Phil Frost - W8II's user avatar
8 votes

Better explanation for beyond-line-of-sight VHF signal reach than "lower curvature to radio waves"

Please accept Phil's answer. It's the sanest one. Now, however to answer: what would be a better answer to this question? Why do VHF/UHF signals usually travel somewhat farther than ...
Marcus Müller's user avatar
8 votes

How to determine frequency and launch angle given a target skip distance?

As an alternative to figuring all of this stuff by hand, you can use a tool like ITURHFPROP which does the math for you, based on statistical models of what the MUF and other variables will be for a ...
hobbs - KC2G's user avatar
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7 votes

Better explanation for beyond-line-of-sight VHF signal reach than "lower curvature to radio waves"

The full question, and possible answers: T3 C11 Why do VHF and UHF radio signals usually travel somewhat farther than the visual line of sight distance between two stations? A. Radio signals ...
Phil Frost - W8II's user avatar
7 votes
Accepted

How can I be sure I'm actually hitting the repeater?

The simple answer is to transmit on the repeater's input frequency, saying something like " < your callsign > testing" and listen for the repeater's courtesy beep (assuming there is one) on its ...
mike65535's user avatar
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7 votes
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What is this burst transmission sequence across the entire band?

It's probably an ionosonde — sending out HF radio signals not to communicate but to measure the reflections and thereby determine the current characteristics of the ionosphere. The signal is probably ...
Kevin Reid AG6YO's user avatar
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7 votes
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Looking for a book that contained a circuit for receiving (literally) underground amateur radio transmissions

Yes, this most certainly was a thing, and people actually did it. This type of communication has been done at ELF frequencies in the 3-30 kHz range. Their linear amplifiers were ordinary Hi-Fi audio ...
Mike Waters's user avatar
  • 8,071
7 votes
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Connecting two sites in the Arctic and Antarctic with a HUGE equatorial repeater? (Science fiction story advice)

Suggestion to OP (and all hams): Play with VOACAP Online to get a feeling for HF propagation. For example here is the whole path: And here is the expected probability of communication on a few ham ...
tomnexus's user avatar
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7 votes
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Why are VHF bands closed all the time?

Solar cycles have almost nothing to do with corporate use of VHF bands. Solar activity is very irregular and corporate use of bands want something that is reliable. Likely corporate users are ...
user10489's user avatar
  • 6,485
6 votes
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Where year 2016 falls in the sun spot cycle for HF propagation?

We're about half way down in the waning years of Cycle 24. We're currently on a 9 day stretch with zero sunspots, the first such stretch since 2010. With the number of sunspots dwindling, we've seen ...
Hamsterdave's user avatar
  • 1,844
6 votes

How is it possible for an HF signal to go around the world when part of it must be in sunlight?

The D region does not affect all HF (3 MHz to 30 MHz) in the same way. For low frequencies, 2 to 4 MHz, the D region absorbs most signals during the sunlight times of the day. However, somewhere ...
K7PEH's user avatar
  • 3,008
6 votes

Can I talk 2 Meter VHF across the United States

There is a list of distance records on the ARRL website. Looking at these, I would say that it might be technically possible to hold the absolute minimum of what could be called a ‘contact’ (e.g. ...
Scott Earle's user avatar
  • 4,619
6 votes

Can I talk 2 Meter VHF across the United States

Sometimes a VHF signal can be heard clearly, thousands and thousands of miles away! The usual mechanism is tropospheric ducting. It's an essentially random, temporary occurrence, not something you can ...
natevw - AF7TB's user avatar
6 votes
Accepted

Two way ham radio to communicate between two stations

The answer to your question involves both technical and regulatory issues. Technical Considerations Radio signals can travel between two locations on earth either by line of sight or by propagation ...
Glenn W9IQ's user avatar
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6 votes
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Loop antenna layout and radiation?

Summary: substantial advantage can be realized for every meter increase in the height of the loop. Other parameters, including the metal roof, are much weaker factors in performance. I simulated a 3....
Brian K1LI's user avatar
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6 votes
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Vertical Antennas

First: do you know about pskreporter? You're definitely getting heard, including one spot on 40m from New Zealand. Sometimes FT8 takes some patience, and it seems like no one wants to come back to you ...
hobbs - KC2G's user avatar
  • 12.5k
6 votes

Practical limits to maintaining coherence in an HF channel

Doppler spreading is the change in received frequency from a distance transmitter due to the rise and fall of the ionosphere along the signal path. When the effective height of the ionosphere rises, ...
pidloop's user avatar
  • 111
6 votes

What is really happening during RF ionospheric refraction?

Solar radiation ionizes the atmospheric gas, creating a plasma with free electrons. The density of these free electrons varies by height, time of day, and solar conditions. Because the electrons are ...
Phil Frost - W8II's user avatar
6 votes
Accepted

If i transmit on the same frequency using two separate transmitters joined together will they both add up in a reciever to produce a stronger signal?

You certainly can, in theory, use multiple transmitters together to produce a signal of higher total power. However, there is a catch: the signals must be in phase with each other. Otherwise they will ...
Kevin Reid AG6YO's user avatar
  • 24.7k
6 votes

What is the best time of day to contact Japan from the east coast?

Around sunrise and sunset (both yours and theirs), to take advantage of "grayline" propagation, which has lower loss than daytime propagation, at higher frequencies than nighttime propagation. In ...
hobbs - KC2G's user avatar
  • 12.5k

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