21 votes
Accepted

Is Morse code a digital, binary mode?

According to Shannon (in A Mathematical Theory of Communication - and who's going to argue with Shannon?) there are really only four symbols in Morse, not five: "dit" (defined as one unit time on ...
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14 votes

Moon->Earth 433MHz link achievable digital bandwidth

Short answer: Math says max link rate is 2Mb/s if you knew the perfect channel coding. Which is still an unsolved puzzle. Long answer: You're calculating a link rate. That is fine, and can be ...
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12 votes
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How does signal strength relate to bandwidth?

It depends on what you mean by "stronger". Ignoring actual limitations of your hardware and just considering the theory of communications, if you have 25 W of transmit power, then you can spread that ...
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  • 23.1k
11 votes
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Are hashes (such as md5) legal in the US

Yes, they are. Generally speaking, authentication is legal, obfuscating is not legal. So you could do a cryptographically signed hash that would be legal in the United States to transmit over Amateur ...
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11 votes
Accepted

Do FCC regulations limit digital data rate?

The Current FCC Regulations (as of July 2018) Parts 97.305(c) and 97.307(f) regulate digital modes primarily by symbol rate. The table in 97.305(c) maps bands/frequencies to specific symbol rate ...
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  • 18.1k
9 votes
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How to receive a signal from multiple sources simultaneously (helical antenna)

I'm working on a system (theoretical at the moment) whereby I wish to receive data from multiple sources all transmitting at the same time. I've read that a helical antenna is capable of this. I'm ...
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  • 23.1k
9 votes

GMRS/FRS data communication

The short answer: this is probably technically feasible, but it's not legal. Part 95 of the Code of Federal Regulations is where all the rules on personal radio services (which includes FRS, GRMS and ...
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9 votes
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Confusion about radio-computer interfaces: TNC, CAT, TRRS, Wolphi Link, ...?

First of all, don't feel to overwhelmed! This can be a bit confusing at the start, but once you understand the pattern and historical development, things will get a bit simpler. So fist of all, you'...
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  • 2,715
9 votes

Is there a legal limit to the bandwidth of a signal used in the amateur bands?

Summary: In all cases, no more bandwidth than necessary. §97.307(a), (b) In data portions of LF, MF, and HF bands, 500 Hz. §97.3(c)(2) In the phone portions of LF, MF, and HF bands, no more than &...
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9 votes
Accepted

Why is a separate repeater required for digital modes? Why can't an analog repeater be used for digital modes?

There is a kind of repeater that can repeat any kind of transmission: it's called a linear translator. It's technically equivalent to an SSB receiver linked to an SSB transmitter. It works for any ...
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9 votes
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Am I really receiving FT8 signals from 12,000 km away on 144 MHz?

I'd say these are simply corrupt. Take for example: 210113_163545 144.174 Rx FT8 -17 1.3 1247 J06NQY A68ITS/R R QM30 A68ITS doesn't seem to be a real call, ...
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9 votes

Am I really receiving FT8 signals from 12,000 km away on 144 MHz?

210115_114630 144.174 Rx FT8 -17 -1.6 685 SIDE LOBE This is probably the one real one of the bunch, actually! The odds of random noise decoding as a freetext message with sensible English in it ...
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  • 9,021
8 votes

Can an SSB transmitter be used to transmit PSK?

The short answer is "absolutely!". :-) I started out using Digipan on Windows, but other software such as Fldigi has been released since then. Audio from the sound card to the mic input --and from ...
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  • 7,515
7 votes

What transfer rates are actually achievable using known digital modes?

You are looking for the Shannon-Hartley theorem. Borrowing Wikipedia's summary, because it's better than what I can come up with: In information theory, the Shannon–Hartley theorem tells the ...
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  • 4,810
7 votes
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Why there is no AFSK in FLDIGI

Fldigi is largely intended for HF operation. From the beginner's guide: Fldigi is a computer program intended for Amateur Radio Digital Modes operation using a PC (Personal Computer). Fldigi ...
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7 votes

Moon->Earth 433MHz link achievable digital bandwidth

Summary: Theoretical maximum in the neighborhood of 10s of megabits per second. Less than that in practice, perhaps a lot less depending on budget. Let's start with the Friis transmission equation: $...
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7 votes
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Can we transfer digital files on radio spectrum?

Radio is analog, and modem converts analog signals to digital signals and vice versa. Everything is analog, yet you can do digital things with the physics that is given to us. As you've noticed, ...
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7 votes

Fast TCP/IP radio modem on UHF band

As you might suspect, the data rate impacts the required RF bandwidth. Besides the data rate, the modulation method, encoding, packet overhead, duplexing, and other factors ultimately determine the ...
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  • 18.1k
7 votes

Is Morse code a digital, binary mode?

The mode hams call "CW" is also called "on-off keying" (OOK) - a hint to the fact that it is a binary code. Dots, dashes and spaces are usually sized in multiples of the "dot time": one dot time on ...
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  • 7,683
7 votes
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Sending a downloaded file on digital: third party communication?

From a Part 97 perspective, the definition of third party communications is: Third party communications. A message from the control operator (first party) of an amateur station to another amateur ...
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  • 18.1k
6 votes

Getting Started with Digital Modes on VHF on Linux

2m isn't a good band if you want to do anything digital. Digital modes just aren't very popular on 2m. I think the only digital activity you are likely to find is: D-STAR APRS D-STAR uses GMSK, but ...
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6 votes

What is a fixed digital message forwarding system?

That's a lot of words for digipeater. These are stations that listen for digital messages, record them in temporary storage, then re-transmit them. This particular allocation is on a secondary basis, ...
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6 votes

How can I decode an AFSK 1200 baud audio clip? (ISS)

Audio which sounds perfectly fine can be noisy or distorted (notably, by FM deemphasis) enough to prevent digital decoding. At a minimum, you should get rid of the microphone step and feed your audio ...
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  • 23.1k
6 votes
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What is "Billion Code" for garage door openers from around 1996?

The billon code refers to a generation of transmitters that could transmit up to ~3.5 billion different codes. Although there were a large number of codes possible, the transmitter always transmitted ...
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  • 18.1k
6 votes
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Is compression "encryption" under FCC regs?

For governments around the world to continue to trust that amateur radio has no nefarious purpose, it is essential that everyone that wishes to, can "listen in" to any amateur radio communications. ...
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  • 18.1k
6 votes
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Relative computational requirement for various digital modes?

Complexity of your question It's hard to make general statements here, because computational complexity is a property of the implementation of a receiver, which usually is a choice given the ...
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6 votes
Accepted

I configured FlDIGI to dislay letters before my PSK31 signal and then I forgot how I did it

I figured it out. In FLDIGI I had video IDS check marked under Configure/IDS/Video. Here is the link to a video on YouTube that clearly explains what I needed to know. https://youtu.be/nwkz0GNpA0I
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6 votes
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Transmit data over HF signal 10,000km away

What you're asking for is a link budget. For HF, you can use software like VOACAP to estimate path loss. There are several ways you might use the software, but to start I'd suggest: Click the ...
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5 votes

Should a MacBook emit fluctuating EMF when WIFI and Bluetooth are turned off?

We would expect no emissions from a disabled WiFi or BT adapter, but as you suggest, all bets are off if your system is compromised. Your broadband detector is only a crude way to check for emissions,...
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5 votes

DMR / DSTAR / P25 Software Encode / Decode

Here is a link to a presentation by Bruce Perens K6BP two years ago: http://algoram.com/dcc2014/AMBE_Exposed.pdf. Start at "Can Hams Use Software AMBE?" I am not aware of any significant changes since ...
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