21

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 followed by one unit time off) "dah" (three unit times on followed by one unit time off) "letter space" (two unit times off) (should follow a dit or dah symbol) "...


14

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 answered using Shannon's Channel Capacity, which gives us the upper limit for bits per second that we can get across a given channel: $$ C= b\cdot \log_2\left(1+ \...


12

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 over as much bandwidth as you want, and you're always transmitting 25 W of power. The quantity which is 25 times higher in the 100 Hz case than the 2500 Hz ...


11

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 Radio. It's worth mentioning that there is some debate as to how legal a cryptographically signed hash would be. I believe it would be legal, so long as it was ...


11

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 limitations in 97.307(f) as follows: (2) No non-phone emission shall exceed the bandwidth of a communications quality phone emission of the same modulation type. ...


9

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 afraid you're misinformed. No single antenna, no matter what the design, can be better than another at receiving multiple signals at once. A receiving antenna ...


9

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 amateur services) are found. §95.631 specifically regulates permitted emission types. Here are the relevant passages for GMRS: §95.631 (a): "A non-voice ...


9

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're confusing connectors and cable purposes. Some cable types for certain purposes have common connectors, but in general, be sure to differentiate between the ...


9

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 "the bandwidth of a communications quality phone emission of the same modulation type." 4 kHz is a good number to put on it, being a typical limit of an ...


9

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 mode because SSB is simply a shift in frequency. Other than the change in frequency, the baseband and RF signals are linearly related. This is also why an SSB ...


9

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, but if it was, it would be a UAE call. The grid QM30 is in the Pacific ocean, about 800 km off the coast of Japan. This is a pretty unlikely combination. The FT8 protocol includes error correction ...


9

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 are vanishingly small. This was probably from someone who worked someone on 2m FT8, and then after exchanging their grid squares, sent a followup message to ...


8

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 the transceiver's audio out to the sound card's input-- is usually used. To prevent hum from a ground loop, it is recommended to use 600:600 ohm isolation ...


7

Most of the common disadvantages for Baofengs et al have to do with usability (e.g. poor user interface, odd squelch performance). The actual reception and transmission power is just fine. The majority of the disadvantages are negated when working with APRS, since it's the APRS modem interacting with the radio rather than a human being. The main thing you'd ...


7

Yes it can be done, and there are some huge advantages: Better use of bandwidth Existing chipsets/support/implementation Low power In fact there's little reason why one couldn't essentially replace DSTAR and competing systems with a standard based on GSM and GPRS technologies. Even for those parts that are patented, the patents running out means we'd be ...


7

FCC Regulations, Title 97.307(f)(8) says yes, you can transmit with ATSC modulation in the US, BUT you can't use frequencies which match US ATSC channels. You would need to find a receiver (maybe PC controlled?) flexible enough to listen to amateur frequencies. As to DVB-T or DVD-S, well, they'll work with about 2MHz of bandwidth instead of the 6MHz ...


7

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 operates (as does most similar software) in conjunction with a conventional HF SSB radio transceiver, and uses the PC sound card as the main means of input from the ...


7

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: $$ P_{r(\mathrm{dB})} = P_{t(\mathrm{dB})} + G_{t(\mathrm{dB})} + G_{r(\mathrm{dB})} + 147.6 - 20 \log_{10} (rf) $$ Insert the values you've given for ...


7

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, when transmitting something digital over an analog channel, you typically use a modulator, and to receive the same you'd need a demodulator, and modem is just a ...


7

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 required RF bandwidth. As an example, the 4G network has a data speed of ~20 Mbps and consumes a bandwidth from to 5 to 20 MHz. In the United States, the 70 cm ...


7

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 for a "dot," one dot time off for the "space" between dots and dashes within a given character, three dot times on for a "dash". Spaces between letters and words ...


7

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 station control operator (second party) on behalf of another person (third party). If you send a file to Bob because you wish to share it with Bob, that is not ...


6

Spreading factor 4, 640 bits/slot, 15 slots/frame, 100 frames/s = 960 kbit/s I don't really understand how the bandwidth for DPDCH is determined like "960kbit/s" for example. There's no equation. It's just another way of stating the information that's already there. By dimensional analysis: $$ \require{cancel} \frac{640\, \text{b}}{\cancel{\text{slot}}...


6

On digital modes (particularly PSK31) RSQ (Readability, Strength, and Quality) is usually used for signal reports, instead of RST (Readability, Strength, CW Tone). There is some interesting history and background information on the RSQ system available at psb-info.net a site dedicated to the RSQ signal report. R = RSQ Readability (Percent characters ...


6

In the US, disaster declarations need to be approved and that declaration with approval must be transmitted to a state EOC before state aid can be approved. Therefore, early in the game, packet has become popular to get that declaration to the state capital. Although HIPPA does not apply to amateur radio (as operators are not healthcare providers), there's ...


6

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 directly into the demodulator program. You don't say what OS you're using, but I have had success demodulating APRS messages using multimon-ng. It can be set ...


6

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, with the primary allocation going to AMTS. "message forwarding system" is defined in §97.3: (32) Message forwarding system. A group of amateur ...


6

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 the data for voice transmitted on that channel relies on a proprietary codec called AMBE. Any software that can encode or decode it is almost surely illegal, ...


6

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 maximum rate at which information can be transmitted over a communications channel of a specified bandwidth in the presence of noise. The Shannon-Hartley theorem ...


6

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 the same code each time the button was pressed, unlike more modern versions where the code changes each time the button is pushed (a rolling code). The DIP ...


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