So this might he a little off topic, but I picked up an SDR with some cool projects in mind. And when I opened SDR programs I quickly realized I had no idea what I was doing. Much of the terminology seemed foreign, etc. What kind of background knowledge do I need to get up to speed with this stuff? Would a few signals/ DSP course suffice to start out?
I recommend getting all 3 ham radio licenses: technician, General, and extra class. In the process you’ll learn all kinds of things and have a lot of the concepts down. You’ll learn about many different aspects of electronics, antenna design, RF propagation, and fun ways to use radios along the way. And you’ll be ready to put it to use right away with your first license.
So if you research learning materials for those licenses you’ll be off to an awesome start. There’s excellent free and paid books available.
I have all three (WT1J) and I found them to be thin on digital signaling, SDRs, and understanding real world signals. I’d suggest getting a cheap SDR and starting here: https://greatscottgadgets.com/sdr/
You’ll learn how to build a basic fm radio using gnuradio along with other cool stuff, like a simple explanation of decibels among other things.
If you know a bit of mathematics the book "SDR for Engineers" is exactly what you're looking for - it covers the right DSP material that you'll need. For starters, it actually covers the sampling techniques SDR actually uses and (it's published by Analog Devices) covers some of the fancy RF-to-Digital System on Chips available today.
Some DSP books (Like Proakis's) are incredibly long-winded and totally detached from the real world (and I say that as a theoretical physics student) and don't cover the sampling topologies that many SDR's use.
Interestingly, I have some very old communication theory books from the 50s and 60s - they are still useful for Software Defined radio stuff today. The only thing they didn't foresee is the throughput of a modern digital filter being as high as it is.
It depends on what your background is already and what you want to do. I took some signals courses in school and we used the Oppenheimer textbook, but that's a lot of math if all you want to do is receive some ADSB signals.
This is an awesome idea. I’ve questioned why the Amateur TV “channels” in the 430MHz range can’t be re-purposed for digital TV or just 6MHz wide pure data channels (over which digital TV could be sent). Much of the resistance is from old HAMs who don’t want anything to change. Hopefully TAPR can get behind something like this as well as lobbying for updates to encryption where TLS over IP over amateur radio is happening.
DATV is a thing on 430. The problem is equipment. MDARC runs DVB-S, I believe. For DVB-S, you can re-purpose satellite equipment. KH6ATV is a proponent of DVB-T (which in theory should be better than DVB-S for terrestrial paths). There is one company in Taiwan that makes DVB-T transmitters and receivers that are usable in the ham bands (available in their E-Bay store), and people have done DVB-T in the ham bands with LimeSDR. BATC has done a lot of work with DVB also. Sorry to be vague, I haven't been keeping up on my reading... about 1.5 years ago I was going to try setting up for DVB-T on 430MHz and 1.2GHz, but life got in the way.
In theory, you should be able to run 780p in a 6 MHz wide channel in the 430Hz band, or even squeeze 480i down to fit a 2MHz wide channel. (The max bandwidth allowed for amateur video in the USA on 430 is 6MHz, DVB-T does have 8MHz wide formats used in some countries for broadcast.)
For those that haven't stopped reading already:
DVB-C -- optimized for cable.
DVB-S -- optimized for satellite path loss and fading, but not for multi-path.
DVB-T -- optimized for terrestrial paths which may suffer from significant multi-path propagation.
ATSC -- The US standard, which unfortunately was standardized earlier than the rest and is expensive to generate and has outrageously poor weak-signal performance, both of which make it a ridiculously bad choice for amateur radio.
My understanding is that ATSC has fine weak-signal performance at UHF in rural areas; it's just extremely sensitive to multipath interference and it doesn't do well with the terrestrial noise in the high VHF range, so anywhere with large flat surfaces (like city buildings) is not so great.
ATSC can easily be generated with GNU Radio and any transmit capable SDR (such as the LimeSDR you mentioned). It's no worse than DVB-S as far as over the air performance. Many TV's will tune 70cm directly (cable channel 58 is 429 MHz).
GNU Radio is also capable of transmitting DVB-S, DVB-S2, DVB-T, DVB-T2 and cable TV 64QAM/256QAM. With DVB-T2, you can even send a MIMO (actually MISO) signal with dual TX SDR's.
What sort of effective bit-rate can you get at 56kbaud and 100kHz bandwidth with the allowed powers? If you can net 4 symbols after any error correction, that would yield the 100kbit TFA wants
Amateur radio, at least in the US, has a ban on encryption, so while we also have signal speed limits that may prevent it, secure sockets are forbidden. I'm not sure how some of the proprietary digital modes get away with it, but I guess money talks.
Arbitrary restrictions like that just make me want to get around them... and reminds me of this phrase I heard many years ago (in the era when encryption laws were far stricter):
"What's the difference between encryption and steganography? You don't know."
Ham radio's purpose and band allocations are not designed to be a secure communication system. They're designed to be a place to experiment with radio, and as a substantial side effect of that can also be a communication system. Adding encryption (and I'd also argue proprietary encodings, but that's another debate) defeats the purpose. Similar to how it can't be used for pecuniary interest.
There are places you can use secure communications, for example in the ISM bands (like wifi) or you can license a chunk of frequency for your own use.
Don't. Follow the rules, and get them changed if you disagree with them.
Amateur radio enjoys the privilege of pretty lax regulation, largely due to the players not making any trouble. Speaking as a fellow radio amateur, we don't want our hobby ruined just because someone wants to be a troublemaker.
> Amateur radio enjoys the privilege of pretty lax regulation
What. You literally have to have a license issued to you personally (no anonymity) by the government to even be allowed to do it. And the rules of what can and can’t be sent are, to my Internet-accustomed mind, excruciatingly onerous. No encryption? No foul language?
1. You need a personal license to identify you, as an operator of a radio station. This is similar to how radios on ships and airplanes work - you need to be able to identify every transmission (even cellphones are uniquely identifiable). This is not only part of the entire sport (we're trying to contact and identify each other), but is also used to identify problems.
2. Just like for airplanes and ships, there are some rules to what you can transmit, as your transmissions can be heard (and cause troubles) for tens, hundreds and even thousands of kilometers away.
3. You have countless frequency allocations available, all over the spectrum, despite the scarcity.
4. Unlike everyone else, holding that license permits you to build your own equipment and transmit with kilowatts with no certification needed. It's extremely easy to cause massive issues with this, such as interrupting cellular communication/gps/wifi an a large area, blowing up your neighbors stereos, and fun things like that.
There's a reason that everything else needs to be tested, certified, and require dedicated band allocations - we avoid it by showing that we have the sufficient skills to practice our hobby and not cause trouble.
Unlike everyone else, we can do pretty much whatever we want as long as we keep it around a kilowatt and talk nice. I consider that to be extremely relaxed rules.
I am reminded of what Chinese people say when they are asked about how they feel about the oppressive government. They say “What’s the problem? We have perfect freedom to do whatever we want, as long as we don’t talk about politics, and who cares about that?”. It’s perfectly normal to them, and they don’t feel particularly oppressed.
Those rules about absolute identifiability are only “part of the entire sport” because you have defined it to be that way. What if Internet chat had been defined the same?
Also, enumerating what you are allowed to do once you are granted a license does not help the argument that the requirement for a license is oppressive.
> There's a reason that everything else needs to be tested, certified, and require dedicated band allocations
Maybe there were reasonable technical reasons in the 1970’s, but now with modern technology, there should be no problem, or at the very least significant relaxations of what the regular public is allowed to do.
I repeat: Having to get an individual government license to practice your hobby is draconian. But, of course, regulations don’t really ever get less restrictive.
It happens to be a hobby that has significant potential externalities, so of course it's heavily regulated. But OP's point is that the initial barrier to entry is so high precisely because once you get past it, nobody is looking over your shoulder, and the limits are lax enough that even very disruptive activity can still fall within them.
Firstly, I doubt that the externalities are that severe nowadays, and with modern frequency-hopping technologies, I believe that it could all be fixed by upgrading existing hardware (even though this would be hard).
Secondly, the original argument was that, and I quote, “Amateur radio enjoys the privilege of pretty lax regulation”. And a requirement to get a government license, tied to your personal name and identity, gated by a large fee and difficult exam, is not my idea of “lax regulation”.
So, there is no large fee at all for getting a Ham Radio license. You can get your license for $15.00 at most testing sites. And if you've studied, you can go all the way to Extra class for that one $15.00
As to the difficulty, children at about 5 or 6 have passed the Technician class test. It takes some studying, but it is really easy. The most difficult part is in understanding the bands that you're permitted to operate on.
In reality, getting a license is easier than it's ever been. There are no more requirements for Morse Code - though some still use it. There is no longer a requirement to go to an FCC field office for testing - your local Ham Radio club can give you the exam. It used to be that you got your Novice ticket, and had to upgrade to Technician within a fairly short period of time - now you begin with the Technician exam.
As for the regulation, there is a real legit reason for this. As Amateurs, we're permitted to operate on a wide range of frequencies - some of which are close to those used for Radar, Wi-fi, and many other services. Some of the frequencies we can use are very long range. The reason for the regulations that exist are in order to prevent interference to other services, to avoid breaking international treaties, etc.
The technical knowledge is important because you're permitted to build your own equipment. It's important, if you do, to know that your equipment is operating properly, so that you don't disrupt many other services with transmitters that are spewing noise and harmonics on many unintended frequencies.
In short, Amateur Radio is FAR LESS regulated than any other service, because of the technical abilities that we have historically displayed. It's a worthwhile hobby and lots of fun. I don't know of any other hobby that has its own satellites in orbit, that has bounced radio signals off of the planet Venus - and regularly uses the Moon or even ionized meteor trails as a reflector for radio signals...
Seriously, given what we can do with the hobby, passing a relatively simple test and paying $15.00 to get your license - and no recurring annual fee ... I don't consider that restrictive at all.
- General Mobile Radio Service (GMRS) which is limited to a set of frequencies in the UHF band, 50w repeaters, and a few watts handheld, and requires an $80? license.
- Family radio service (FRS) which is limited to store-bought handheld units with 0.5W maximum output
- Citizens Band radio which is limited to 40 channels at 4 watts and is highly abused by its users and relatively unenforced
- Multi-Use Radio Service (MURS), which is limited to a six VHF channels and 2 watts and shared with many users
- Business Band/LMR Part 90, which is licensed and regulated for business/commercial use with many other shared users
- Microwave, which is licensed and heavily regulated
- Broadcast radio, which is licensed and very heavily regulated (and is one-way only)
None of these services allow you free reign over a wide spectrum of radio with home-built equipment for the purposes of experimentation and recreation, except for the experimental license, which only allows you specific frequencies, power limits, and other regulations based on your license application and grant.
I agree that amateur radio regulations are relatively relaxed, if not very generous, liberal compared to the other radio services.
Radio spectrum is a limited and shared resource. It makes sense that it's licensed and regulated. But compared to other parts of the spectrum, the license is cheap and easy to get and the regulations are minimal. It's a public space for experimentation. If you don't want to be seen in public, go to some other area of the spectrum.
I agree with the regulations on spectrum and power usage (i.e. "don't shout over someone else"), since it is a shared medium, but definitely not with restrictions on content.
My guess is that they're not, strictly speaking, "encrypted" any more than the first guys to use FM were "encrypting" their transmissions. They are receivable and decodable, you just need the right equipment.
I agree that these things should be kept off the air, but I don't think it's a "money talks" situation.
This is it exactly. You may not try to hide the information that you transmit, but you sure as hell can make it obscure as fuck. Just imagine the fictional conversation:
FCC/CRTC: On July the 1st at 14:00 you transmitted an undecipherable message on 28MHz.
Amateur Radio operator: I used y-modem protocol to transmit an image using 7P1 (7bits Parity 1 Stop bit).
FCC/CRTC: but's that's stupid! Nobody has used that in 40 years!
Is this a thought experiment, or does the FCC really do this?
It's hard for me to imagine that they have an army of radio engineers to go looking at all signals, figuring out which ones are "undecipherable", physically identifying the transmit locations and then determining who did it.
The entire culture works hard to weed out anybody that doesn't follow the rules. If you do something you're not supposed to, there's a good chance someone will figure it out and report you.
Undecipherable signals in strange places present an interesting challenge that the ham radio community does rise to explore. During the cold war ham radio operators spent years analyzing and characterizing over the horizon radar systems (The Woodpecker) and other strange signals like numbers stations.
Its especially common these days with the advent of software defined radio, spectral displays and large amounts of storage for operators to come across a strange transmission and record it for further analysis, often posting in forums and sending the recordings to other people for them to try and analyze it.
And some times those recordings are sent to the FCC and the FCC sends out strongly worded letters.
If it really gets bad, the FCC will act and IIRC they average about 20~50 or so fines a year.
Encryption is optional (or not available) in all of the proprietary digital modes used by amateurs, so amateurs simply don't use it even when the radio allows. As a practical matter enforcement can actually be quite difficult and I'm sure there are some folks doing it, but people on the amateur bands generally obey the rule in my experience.
We're talking about encryption, though. Isn't the core of the PACTOR debate related to it being proprietary, not that it's encrypted? Transmitting in a format that is not readily decoded is also problematic legally, but to me there's a major difference between using a proprietary format and using actual cryptography to encipher a message. The latter is uncommon in amateur use in my experience, but I'm only an occasional ham so maybe I'm just not aware.
Depending on latitude and the sailor’s pocket, I could see Sailmail users being driven to StarLink if the FCC doesn’t allow Sailmail’s continues operation in its current form.
Tons of amateur radio links in the US are encrypted. Just look at literally any repeater. The myth that there is no encryption on ham channels is as wide spread as it is misunderstood.
It is allowed to used an encrypted connection to administer a remote repeater, like for amateur satellites. Only the control link may be encrypted. The repeated signals may not, just like any other amateur transmissions.
I look at lots of repeaters. I'm a repeater engineer for our city radio club. Not one has any encrypted links, unless you're talking about echolink/allstar/D-Star/YSF, in which the audio is transmitted via the internet through various protocols to other gateways, repeaters, reflectors, conferences, and end users.
Even the DTMF tones to control repeaters aren't encrypted. Some repeaters do obscure the re-transmission of the DTMF codes by muting the output, but this is legal.
Interesting. I’ll have to revisit this topic. My understanding was that the use of encryption was restricted while the parent was saying it is illegal.
To clarify what percentage of your clubs repeaters are reachable through one or more encrypted connections?
Looks like you spent about 1000x more $ on SDR, RF bits, and computer hardware for that setup than the rpi/rtlsdr options explored in the main article.
Oh this is awesome.
In ancient times I set up email over uhf in a remote village in bougainville (the only link I can find is a paywalled pdf https://shop.ata.org.au/shop/renew-issue-84)
We had to pretend to be a ship the mv sunrise to access a system that ran out of san diego that was only licensed to provide service to ships in international waters.
There was an internet provider in the solomon islands that did something similar, but for political reasons they were not allowed to help.
Ignore open IP over VHF/UHF if anyone wants a challenge I found out recently that...
People have been able to eavesdrop on homes by targeting pretty much anything containing metal coils (including appliances) with advanced HAM radio equipment since the early 1970s.
