A friend of mine and myself are working on a computer controlled aircraft. Its basically a trainer that will be controlled via laptop and send back gyro information on the axis.

The main obstacle so far seems the FM Dual Conversion system. Can anyone offer me some help or information on how I would go abouts working a system that is fed information through the serial port.

So far I understand that the radio sends the commands through 2ms pulses in approximately 20ms frames. OK, great.

I also understand the ON position is given by a 5kHz shift in frequency (down for Futaba) and a 3.3v level.

The part i get confused on is this.

In FM, since the signal is always being sent as either original or 5kHz modulated, when does the voltage change, or is it always 3.3 volts?

Also, this dual conversion is really confusing! I've read the site !QUOT!Everything You NEVER Wanted to Know About Radios!QUOT! and it helped a lot, but I am still struggling with the dual conversion.

Additionally, does anyone know how to build a transmitter for this purpose that will connect to the computer? I understand the principle of FM, but what is the practice that actually makes it work? How does the frequency change? does it just broadcast on another freq. using a different crystal? Could someone offer some clarification on this?

Finally, I understand this is a weird and complicated job and I've asked about a million (exaggeration) questions in this post... so if you have information or links or connections to people with info on any of these topics or any of _these_ topics...

<edit></edit> After reading this, read the third post to perhaps understand me clearly. I don't think this makes too much sense as it stands right now information about the following topics or the third post would be appreciated, thanks! [[ Tuesday November 25 20003]]

radio protocols

FM protocols

how to make an FM transmitter from computer

dual conversion

how to make something that will transmit equivalent to my FUTABA Skysport 4, Dual Conversion 72.870MHz transmitter,


I'd be absolutely greatful!

Thank you very much

Chris:

To start with, sending a signal from the airplane to ground is legal on a very few frequencies, none of which are available to youor Futaba transmitter and reciever. And the legal ones require a license, in most cases.

The way to start, in my opinion, is to contact a radio amateur somewhere near you, and get an FCC technician license. This will open the transmit frequencies for you, then get a copy of the Radio Amateur's Handbook, Just about any question you might have on the tx and rxsystems will be there, and possibly anencoding scheme you could use.

Your post said you wanted to send the gyro signal back, but you also said a signal your Futaba could use. This is unclear to me, I don't know what the desired result is. If I know that I might know an easier way to reach your goal.

And incidentally, an AM rc transmitter isn't AM, and an FM tx isn't FM. What is generally called AM merely switches the carrier on and off, and the "FM" uses FSK - frequency shift keying. An "AM" rx with a really high Q would work with an "FM" tx on the same channel, as the shifted frequency would be rejected, and "Sound" like a break in the carrier.

So tell me what youo want to get, maybe I (or someone else) can help.

Bill.

Sorry, I was really tired last night when I wrote that I guess. lol

What i meant to say is I want to control the aircraft from a computer. So I am trying to build an FM Transmitter that can broadcast on the same frequency as teh remote transmitter.

I would send the information back on whatever channel I could legally do so from or I would get a license for that. Basically it would be two different radio systems

1) A computer sending Futaba commands to the futaba receiver on its frequency (mimic the tx)

2) a small transmitter on the aircraft sending data back to another receiveR (not futaba, something I will design actually) which is fed to the computer controlling the airplane


Sorry about the confusion, hopefully this will help you understand me

IF I understand correctly you want to build an interface to control your plane from
your computer. If so, then why not just use an existing radio tx replacing the 4
stick pots with 4 D to A converters?

That should be very easy to interface to your computer. You could drive it via
your printer port and you would not need to mess about building a custom radio TX
from scratch.

Nick

Oh that would be amazing to do! do you have any information on how I could go about doing this? It sounds like a really good way to go but I'm not quite sure how to create such adapters.

Failing that, do you know how i COULD make a tx from scratch lol

Well basically you need to take an existing radio and measure the voltage
with repect to ground of the center wire on each pot at various throw positions.
As you move the sticks the voltage will change.

That voltage change is what you need to know in order to simultate the joystick pot
from the computer.

You can get a D to A chip which basically you put into the memory map of your
computer so that you can address it and write data (numbers) to it. Usually the
bigger number you write the greater the voltage on the output pin. Once you get
that working it will be a simple interfacing job to connect the output to the middle
wire instead of your pot.

Get yourself a basic book on micro processor electronics to see how to interface
the chip. You can use a latch and the printer port if you don't want to interface directly
into the computers memory address space. It's not hard but you'll need to do a bit
of investigation to design the circuit.

Please have a look at this announcement:

http://www.rcuniverse.com/forum/USB_...1872042/tm.htm

This will allow a USB equipped PC to send out PPM signals, which can be connected to the TX trainer port for RF transmissions.

Tom

Why do you want to use the aircraft radio? Use something like WifI. You can get [potentially] greater range, greater bandwidth, and it's in the legal range. You'll get bored of your project, though, because it's a very common thing that many people do. A UAV is the obvious next step, but discussion on that is not allowed on RCU, or as I like to call it, GestapoU.

Dongle, The term "dual conversion" simply means that the receiver mixes the received signal, generally down in frequency, two (2) times in the IF strip portion of the receiver. Most likely those frequeinces would be to 9MHz first and then 455KHz. This occures prior to demodulation and provides selectivity, that is to say that the receiver is more imune to adjacient signal and image interferance. If you do not understand those terms let me know and I will attempt to explain them. As an alternitive you could go to your local library and read about receivers and FM communications in the ARRL hand book. The older ones like 1960's thru 1980 will be more tecnical as the amature community newcommers have been "dummed down" just like the rest of the education establishment.

In reference to the FM signal from the transmitter, the carier is always transmitted and upon a command input to the FM modulator the output of the transmitter is shifted in frequency. For narrow band the amount of shift is 5 KHz and wide band is usually, but not always, 15 KHz. This depends on application and the amount of inteligence required to be transmitted.

As to the ability to transmit back from the receiver you could read the section on "repeater design" in the afore mentioned reference source.

I hope that some of this will be of help to you and please excuse my spelling but I am a TEXAN HI HI.

If you should have any questions that I might answer you can "e mail" me @ [email protected]

73 fly the airplane first

Lee K5MRC

Hi Bill I just saw your answer, NICE, what is you call? I signed with mine. 73 and have a good week.

Lee K5MRC

If you want some ideas or direction, check here...

http://kd7lmo.net/nsrv.html

Ryan
kc0lmo

Lee:

I used to be W4HZP, but that was many years ago. I dropped ham radio when almost everyone became appliance operators. To me the fun was building the stuff and making it work.

Just like model airplanes, to me the ARFers are the appliance operators of model aviation.

Not that I don't have some ARFs, as I also had some ham appliances. But I really get more enjoyment from the building than from the flying.

Bill.

Is there any way to remove or edit previous posts ?

If anyone with enough admin priv. would mind, please delete this thread.