Wireless communications

@VE1DX

I'm not sure what you are getting at with the 'Hams' angle, but communication between robots, weather stations, lighting, heating controls etc, via a number of wireless communication technologies is probably what we all play with in our projects.   

For my current 'big' project which is a home automation project certainly has found me tinkering with wireless control. Nodes built on rpi's and arduino send and receive instructions over WiFi (using MQTT ) with a few zwave nodes as well.  How 'smart' all this is is dependent on my central control program so it may be rather a dunce. ?    Shortly I will be experimenting with some LoRa boards to reach the parts where Wifi does not reach. 

Are you alluding to producing electronic circuits to actually do the communications bit?

Posted by: @ve1dx

I wonder how many members tinker with wireless control of anything.

I'm currently using a very simple WiFi set up using the ESP8266-01 module.   I'm using UDP instead of TCP because it's far easier to program and serves my purposes.   The ESP8266-01 module actually had a microcontroller on it so it's fully programmable.  It also has connections for serial I/O to the devices I want to communicate with.

As far as I can see this set-up has no limitations in terms of the type or amount of data that I need to exchange in  my projects.   However it does have some range limitations when my robots evolve to include outdoor activities.   But then again, I'm not sure that any radio signals are going to have much further range without a need for something like a Ham License.

I remember years ago when I was into RC planes, I bought an RC controller from Heathkit that had frequencies that required a Ham radio license to use.    I never got a Ham license, although I did build several Ham receivers and even a transmitter.  I just never used the transmitted.  I just bought it because I love building electronic kits.  Well, I was  planning on getting the Ham license but I never did.  I guess I just wasn't that interested in talking with other people on the radio.  I was more interested in the electronics than in the actual communications aspect of it.  I didn't know anyone else who had a Ham radio that I could talk to anyway.

My uncle was big on Ham radio, in his "station" he had post cards plastered all over his wall from people all around the world.  I watched him "operate" and all I saw were people exchanging call letters, having a short conversation about the weather, and then promising to send each other a post card.   That didn't appeal to me.

So in short, I really didn't see much use for Ham radio, at least for me personally.   But I did like the electronics end of things.

And of course now, I can see the benefit of having a Ham license to operate more power.  If I had a Ham license my robot could go further while still remaining in radio contact with the base computer.   As it is now I need to work on having my robots become fully autonomous when out of radio range.  And perhaps that's really not a bad thing.  It will force me to create more autonomous software for my robots.

What I meant by the Ham "angle" was, as has been pointed out, if you have a Ham license, you get special permissions from the government in your respective country.  For example, in Canada, you can transmit signals on frequencies allocated to Amateur radio operators, and you can use a heck of a lot more power.  Like 1,500 watts with the proper equipment.  It's 400 watts maximum in the UK, but the idea is the same.  Not something you want to do with an Arduino or Raspberry Pi.  I thought we'd use this forum to discuss milli-watt communications on frequencies that don't require a license.  Bill covers this in his cautions in the 433 MHz YouTube video.  I didn't want to "hijack" the conversation and slant it toward amateur radio, that's all. The Internet is already full of Ham radio discussion groups.

@robo-pi, I was like your uncle!  I communicated with every other country in the world (literally) and have 100s of postcards to prove it.  After 25 years, it got old.  What might regain a lot of interest is if we could develop low power (milli-watt) technology that would communicate over vast distances.  In 1985, imagine the thrill of talking to someone in Australia, for example, with a piece of wire strung between two trees and 100 watts.  Nowadays that's ho-hum, but doing it with 100 milli-watts keyboard to keyboard, or bouncing signals off the moon aren't.  Yes, some people do that -- it's called EME (Earth-Moon-Earth), and it's something I never tried, and likely never will.

Posted by: @ve1dx

Like 1,500 watts with the proper equipment.  It's 400 watts maximum in the UK, but the idea is the same.  Not something you want to do with an Arduino or Raspberry Pi.

Why not?  The Arduino and Raspberry Pi are just computers.   You don't need to run the 1,500 watts through the Arduino or Raspberry Pi. ?    

All they would be doing is providing the message to be transmitted or receiving the incoming signal.  The radio equipment is a totally separate thing.

OK, I understand the technology aspect, but you still need a license to transmit any amount of power, and the useable spectrum is in high demand.  In theory, you could generate a digital signal with an Arduino, amp it up to 40-50 watts with solid-state components and then run it into a tube amp.  Then send it out at 1500-2000 watts on 14 or 21 MHz if you have an Advanced Ham license.  My thoughts were instead to do it in with some intelligent DSP technology that used low power that everyone could use — the 433 MHz stuff on steroids in terms of efficiency.  I think a guy at MIT (Amateur radio call is W1JT) has developed something like that called J8, but I never fooled with it.  Anyhow, that's the point — no Ham license needed. Stick with 100 milli-watts or less.

Posted by: @ve1dx

My thoughts were instead to do it in with some intelligent DSP technology that used low power that everyone could use — the 433 MHz stuff on steroids in terms of efficiency.

That's the direction I am currently thinking of going.   I have the 433Mhz modules, and from what I hear, under "optimal" conditions they can be used to transmit and receive to potentially 3 miles.    That includes using directional antennae at both ends, and having a fairly unobstructed line of sight path.   In other words, 3 miles is about the max you could hope for with "dependable" communication.    I only need about 1/2 mile.  Maybe not even that far.   Even a 1/4 mile would be useful for me.   But it's not line-of-sight as there are both forests and hills between the communication points.  I could use directional antenna though since both the base and the robot would know each others location.   The base antenna could be raised up on a small tower as well.  I haven't experimented with anything yet so I have no clue what kind of results to expect.  All I know is that my current WiFi set up isn't going to reach anywhere near far enough.   Not sure if WiFi could be beefed up to reach 1/4 mile or not?  I do know that when I go to the Library to use their WiFi I can connect to it from the parking lot across the street.   I can also see the MacDonald's WiFi showing up and that's down the street a bit.   Not a 1/4 mile down the street though.

But yeah I'd like to have at least 1/4 range to communicate with the robot, 1/2 mile would be even better.   Not really planning on having the robot go any further than that from home.   So I would only need a few watts of power.  But even a few watts requires a Ham license doesn't it?

And even with a Ham license could I still use the 433Mhz freq?  If 433Mhz one of the Ham Radio frequencies.  I'd probably just have the "Technician License" I don't think I want to bother having to get a General class license.

I found this for the Technician Class Ham Radio

Would that "above 50Mhz" include the 433Mhz?  Could I just then use the modules I have and increase the power?

Yes, 433 MHz is in the above 50 MHz category, so the Technician class all you'd need.  That's an easy test to pass.  433 MHz is within the 70 cm Ham band.  The ITU allocation worldwide is 430 to 440 MHz, but this varies somewhat from country to country.  In the US, it's 420 to 450 MHz, and in Canada, it's 430-450 MHz.  Hams typically use less than 25 watts on that band.  The "rule" in Canada and the US is to use the minimum necessary for reliable communication, and often 3-5 watts is enough for 10 miles or so if you have a clear line of sight (FM voice).  I'm sure algorithms exist that will transfer data a lot more efficiently than FM voice, so it's possible 1/2 a watt or less would work.  I don't know how much power those "off the shelf" 433 MHz modules produce, but likely very, very little.

 You can build (or buy) quite high gain 70-cm yagi antennas. Because the wavelength is so short, these antennas are small.  It's not unusual to find something about 4-feet long with ten elements that has 12-14 dB gain.  That would be quite directional, but for what you want, I think ideal.  Even 1-2 watts ought to be good for several miles or more.  Also, in my experience, VHF and UHF signals don't have to be an exact line of sight.  There's enough signal that "bounces" off buildings or bends slightly that you often get surprising results.

Controlling a robot from 1/2 mile distance ought to easy. You could use a yagi something like I mentioned above to transmit (possibly even half as long with 5 elements), and a simple vertical to receive.  Those little coils that come with the 433 MHz antennas you get online are very inefficient.  They are excellent for across the room, but for what you are proposing, I think running a piece of high-quality coax cable to a yagi from your control circuit to a yagi aimed at where your robot is would be necessary.  On the robot, a 1/4 wave vertical with a few radials around the bottom would be all you'd need.  a 1/4 wave vertical 16.5 cm (about 6.5 inches.)  I think that would be reasonably simple to install on a robot.  Have a look here:

https://m0ukd.com/calculators/quarter-wave-ground-plane-antenna-calculator/

That's a neat project!  I hope you can get it working.  Let me know how you make out.

Sounds good!   I've always wanted to get a Ham Radio license just to be able to play around with radio control and now with my robot projects I finally have a reason to actually needs this.   The Technician Class license sounds like all I would need for my purposes.   I'll have to look into what it takes to obtain that license.   And then I can get into building a nice Robot Control system.

Like I say, I can't really see a need to control the robot more than 1/2 mile from the house, and even that would be quite far.   But it would be nice to have that much capability just to be sure that it's always going to work dependably even at closer distances.

It's going to be quite some time before I actually need this kind of control.  But if I start looking into getting the license now then I'll have it when I need it.   For the immediate future I'll have to set up the 433Mz modules I do have and see what I can accomplish with just the 100mW power restriction.

As you point out I probably won't need more than a couple watts.  Even 5 watts would probably be overkill.  So I won't need to be building any seriously powerful transmitters or anything like that.   Probably better focusing my attention on making the most efficient antenna designs.   The base antenna won't be a problem.  But on the robot end I'd I might need to be creative.  

My robot will eventually have a human-like head. I'm already thinking of putting a straw hat on her to disguise the camera that will be her eyes.  Now I'm already thinking that I could  have her carrying a parasol around with her and that could be RF antenna in disguise. ? 

I mean, she's going to be on a wheeled base, so it's not like anyone will be mistaking her for an actual human.  But still, I'd like to keep her top half as human-like as possible just for fun.

But yeah the Ham Radio Technician license sounds like just the ticket.

It's going to be fun! I'll have my robot to talk to on the Ham Radio.

"Base to Alysha, where are you?  Over."

"I'm almost a quarter mile from home and I'm frightened, come and take me home!"