Comm Bands and Ham Licences

[ElectroLawndart]

Taking a look at communication options for down links that can handle 25 to 30 mile ranges LOS, my best option is packet radio modems. Which means that I should get my Ham license.

My question is: How hard is it to get licensed and is there anything I overlooked that would not allow me to use packet radio with a "no code" license?

Thanks
Dart

[radiohound]

A tech no code amateur radio license would give you the ability to operate packet radio on 144 mhz or higher. This test involves 50 questions (at least it used to) of a 507 question pool. They are multiple choice, but studying is required.

There are some sample exams here: http://www.eham.net/exams/

The Kenwood th-d7 radios have built in 9600 baud packet.

The maxstream 9xtend data transceivers have close to the range you are talking about without a license required. They get a 14 mile range at 9600 baud with dipole to dipole. This can be extended a bit if your "base" station had a directional antenna pointed in the direction of your model. They advertise 40 mile range at 9600 baud with directional antennas at both ends (a bit harder to do with a rc plane). And 7 mile range with two dipoles at 115,000 baud.

Here is the data sheet for the Maxstream. http://www.maxstream.net/products/xtend/module/9xtend-datasheet.pdf I have not tested mine yet, but once I do I will let you know how its working for me.

Walter

[Mr.RC-CAM]

How hard is it to get licensed and is there anything I overlooked that would not allow me to use packet radio with a "no code" license?The no-code Technician class license is not hard at all. Visit arrl.org to find out more.

You can use your ham license for telemetry in a number of formats. But like all ham communications, none can be encrypted and your call sign must be sent every few minutes. While you study for the exam you can learn more about the requirements.

Packet radio is a digital person-to-person communications scheme that is basically used to send ASCII text messages. Unlike telemetry applications, it is a 2-way communication (an FCC Part 97 requirement). Baud rates tend to be fairly slow, mostly under 9600 baud. But, I hear it can be pushed to 56K with higher cost TNC's.

I'm not sure what you intend to send, but if it is real time video, then packet is not the digital protocol to use. Instead, Digital-ATV (DATV) is available for that. I don't know much about it other than it is very new and not {yet} as popular as slowscan or the other ham ATV communication methods.

RC-CAM

[kd7ost]

Here's another source for practicing the test. I found this an easy way to go.
http://www.qrz.com/testing.html
Just spend some time hitting this site and going through the practice tests until you can get a better than 70 percent every time. There are only 35 questions on the test for Technician or General class. But, there are 250 to 300 questions in the pool. You don't know which ones will be on your test. It sounds worse than it is if you have technical inclinations. It should be rather easy to do for most people.

Dan

[Mr.RC-CAM]

FWIW, it is possible to just study the test answers without regard to what they really mean. However, that really puts you at a disadvantage. So, besides doing the online practice test exercises, I would encourage you to obtain a intro ham guide (library, Radio Shack, Borders, etc.) and learn as much as you can about the ham hobby, the regs, and basic RF stuff. It is really not that much more work and you will be better prepared for your RF projects.

RC-CAM

[ElectroLawndart]

Thanks All,

I have the intro booklet that the ARRL published. I was just wondering how hard the test actually is. I guess it's not very hard. I do intend to study for this. I don't believe in having just the answers, this is not knowledge, I want the background and reasons behind the answers. There is a local ham club here in the San Fernando valley that gives the test every other month. I'll be taking it in couple of months.

Mr RC CAM,
Thank you for the information. I have always been impressed by the scope and amount of knowledge you have. Initially I will just use 9600 baud for the uplink and downlink. Position updates, aircraft attitude, aircraft condition(voltages, temperatures, etc.) for the downlink. Course and waypoint updates and such for the uplink. I won't be transmitting any video yet, just strictly an off the shelf, digital still camera with images stored on it's memory card.

Don't want to lose focus and get too bogged down with complexity. Phase 1 of this thing is only suppose to be a retreival experiment. Gotta be able to get the derned thang back before I go hangin' expensive frilly things on it. :D

Thanks
Dart

[kd7ost]

, it is possible to just study the test answers without regard to what they really mean. However, that really puts you at a disadvantage. So, besides doing the online practice test exercises, I would encourage you to obtain a intro ham guide (library, Radio Shack, Borders, etc.) and learn as much as you can about the ham hobby, the regs, and basic RF stuff. It is really not that much more work and you will be better prepared for your RF projects.

RC-CAM

I couldn't agree more. It's tougher for the guys who don't come from an electronics background at least in a hobby capacity let alone as a trained job. There are many things in the test though that are geared towards your start in Being a Ham Radio operator starting out in talking to the whole world. Many UAV guys just want to legally operate the HAM AV gear and track via APRS. There are parts of the test that you need to know the answer to in order to pass, but unless you go on to be a Bonified Ham Radio operator, you'll likely forget in the first year. Things that don't help you do Video downlinks. Like, "What is a signal returned to the Earth by the Ionoshere called", What is a satellite Perigee", and "What is the term for the location at which the control operator function is performed?" (There's a hundred questions like that) These things tend to go in one ear and out the other when the test is over unless you have built and frequently use your own Ham Shack and stay connected with the talkers. I do support at the very least a self study if not a schooled educational process with at least basic electronic theory and intro to RF. Some of you guys, like Mr RC Cam are quite skilled and have helped us out in many ways and at many times. He brings a lot with skill in both Hardware and software. Thats not a common blend.

Dan

[LukeZ]

I just studied up and passed my Tech exam a few weeks ago, for the very same reason you are, in order to be able to use Ham radio on my UAV project. My sole study guide was the oft-recommended "Now You're Talking." Used to be carried by Radio Shack but I don't think they do anymore; I got my copy from Amazon (http://www.amazon.com/exec/obidos/ASIN/0872598810/qid=1114322237/sr=2-1/ref=pd_bbs_b_2_1/102-0321796-5360973).

Frankly I found the book very poorly written, and reading it straight through, while reviewing the questions at all the intervals that they recommend, is truly a maddening experience (lots of page flipping). I think the authors are well-intentione hams, who are probably really good at what they do but less-than-stellar book writers. However, the entire question pool is in the back of the book along with the answers. They're all multiple choice and the questions in the book will have the same answers as the questions on the test. So not only can you study the right answers, but you can also see what the misleading ones are going to be.

Although I found it frustrating at times, I do have to say that the book does in fact tell you everything you need to know to pass the test. I passed mine without missing a single question; I recognized them all from my studying. And I felt like when I had completed the book that I had indeed learned quite a few new things. Finally, it's an ok reference to have around on some of the basic stuff, though you'll probably want to buy a better reference eventually.

Ironically, it was through studying and learning about Ham radio that I became aware of how limited its use would probably actually be for me, in terms of long-distance telemetry. However, if you want to transmit video and do some other things it's useful. And also, completely aside from the UAV connection, you never know when it might come in handy. I'm thinking of getting involved in some search and rescue stuff, and having a ham license is almost a prerequisite for that...

[ElectroLawndart]

Ironically, it was through studying and learning about Ham radio that I became aware of how limited its use would probably actually be for me, in terms of long-distance telemetry. However, if you want to transmit video and do some other things it's useful.


LukeZ,
What did you find limiting about using Ham radio for long-distance telemetry? This is exactly what I'm going to be using Ham for. Even though will be dropping my glider from about 12miles up, I would like the ablilty to send it on extended photo missions. Say about 50 miles with a directional antenna on the ground. Gotta use an omnidirectional antenna on the A/C just in case it ends up doing some wild gyrations on the way down. :rolleyes:

Thanks
Dart

[LukeZ]

Dart,

For 12 miles, and even up to 50 miles, ham will probably be fine for you: as you know from the High Altitude Glider Project (http://members.shaw.ca/sonde/index.htm). He was getting reception up to 65 nm away, he says.

I guess when I mean long distance I mean greater than 50 miles or even 100 miles, say 1,000 miles. Before I knew anything about ham radio, just some terms and basic concepts, I had this idea that I could put a DX rig in my UAV and (if conditions were right), somehow communicate with it pretty much anywhere on the globe. After all, the guys on the Kon Tiki carried along a little hand-powered generator on their raft and were able to talk to other hams all over the world, from right in the middle of the ocean, and that was in the 1940s. However, as I say, that was before I knew the details about this stuff, details I learned in studying for my exam. Even if my UAV had the ability to carry the weight of a High/Medium Frequency transmitter (the frequencies used for long distance), and the large antenna it would require, the wavelength isn't even well suited to digital comms: the communication mode at that level is typically morse code.

Then I thought, ok, I'll have a small transciever aboard and I'll use packet radio: there are repeaters all over the country. I'll just have a database of repeater frequencies and coordinates (http://www.circuitcellar.com/library/print/0804/Worstell_169/index.htm) in memory on my onboard computer; the UAV will compare its known location to the database and attempt to transmit to the repeater nearest by. However, once again after talking to some hams more knowledgeable than I, this didn't seem to be a very workable solution, partly because of the low throughput, and partly because of some other things which I still don't quite understand... :o

For something that needs to be light weight, mobile, and able to communicate digitally over very long distances, I don't think ham radio is the ticket: at least, there aren't any modes that satisfy those requirements to my knowledge, but I'd be much more than happy to be corrected. :)

APRS is the only thing I can think of. It's fine, and I'll probably use it. But it only provides limited information at relatively slow refresh rates.

I think for very long distance, digital communications, cellular or GSM is the way to go. You can even use it to transmit small pictures, as anyone knows if they've purchased a cell phone lately. Can't really do that with morse code.. :rolleyes:

[ElectroLawndart]

I think for very long distance, digital communications, cellular or GSM is the way to go. You can even use it to transmit small pictures, as anyone knows if they've purchased a cell phone lately. Can't really do that with morse code..

I am hesitant to use celluar in a UAV. Mostly because it requires being close to civilization. The idea of a flying robot asking "Can you hear me now?...Good." then moving on, is pretty funny.

I've thought about long range communcation in the hundreds of miles range using a trailing antenna. But just like you, soon realized that the mass of the equipment would be prohibitive. Just to overcome the drag of the trailing wire would require a larger IC motor.

You can send pictures with morse code. You just gotta have REALLY FAST fingers to send and copy code. :D

Thanks all.
This has been a slow project, but with the start of this forum the pace is picking up.

Dart