Lynx

A transmitter with a buddy chord, does not need to be FCC certified to work with another transmitter that that buddy chord is plugged into. Transmitter modules have to be certified with the transmitter that they're used in for type acceptance. I've seen 'dumb' buddy boxes sold (no RF components) that you can use in a trainer system as well. Is there anything legally wrong with generating a PPM frame from an external circuit, and plugging that into a buddy chord for the 'certified' xmitter to transmit? If not, is there anything legally wrong with interfacing between the xmitter and module, as long as you don't alter either one directly? A microphone doesn't need to be FCC certified to plug into a transmitter that transmits the signal the microphone generates. The reason I ask this is because I'm trying to avoid the FCC altogether in the creation of something that will interface through a buddy chord to an xmitter and I don't want problems if I decide to sell it. I'm not going to give the FCC a chance to rake me over the fee coals in trying to get a type approval for my product. Any help or direction to applicable FCC law would be appreciated, especially from HAM users.

staggerwing

My Feedback: (5)

If you hold a valid Ham license you can design, build, and/or modify your equipment all you want as long as it operates on an authorized ham band (i.e. 50 mhz/6 meters). The same rules and regulations for 72 mhz equipment do not apply to hams.

Rich AD9V

dirtybird

My Feedback: (5)

I think you probably should ask the FCC. I don't think they would rake you over the fee coals. I sure wouldn't want to base any business I wanted to create on an answer I would get here.

Lynx

Just trying to get an idea.

smallrc

Just food for thought... The Kraft transmitters that use plug-in modules
must be modified in the RF module and on the encoder board
to meet the current narrow-band specs. Using an un-modified
transmitter as the "buddy" transmitter, is likely not meeting the
narrow-band requirements[sm=thumbdown.gif], even though a narrow-banded transmitter
is doing the broadcasting.

Later... Kenny

Lynx

That makes no sense though smallrc.. The part that generates the PPM frame has nothing to do with RF energy by any stretch of the imagination and can't possibly cause interference. Then again they may not use the kinds of modules I'm talking about.

apteryx

Ths is an AM discussion right ?

The part which generates the pulses CAN affect the signal width because the rise and fall times of the pulses affect the AM modulated sidebands. One of the techniques for narrow banding is to add a capacitor or resistor/capacitor network to the pulse train thereby
giving the pulse sides some slope. This reduces the overall AM signal width. Since that signal is both on the encoder board and the
into the RF board, the change is probably made on the RF board. On the Kraft units with plug-ins you would have to take the module apart and it's probably easier to modify the encoder board, but you definitely have to go inside the RF module for a frequency change if it's one of the old frequencies. Just my opinion, would like to hear from the guys who made the changes and hear what they say.

A FM transmitter probably won't have the problem in the first place because the pulses are used for a small frequency shift and would be inherently narrow. Generic buddy boxes should be fine for FM, I would think.

Now, back to the original question. If you attach something else between the Encoder and the RF Module other than through the buddy cord, you are violating the "don't mess with the internals" rule (does not apply to 50Mhz and 53Mhz ham licensed units). If it's the encoder signal from a generic buddy box it's OK, but you have to be in control of what's transmitted. If it's uplink telemetry or some other data stream, it's not allowed as a 72Mhz "R/C signal".

quemazon

My Feedback: (1)

I think you'll be fine. As long as your device doesn't generate any significant RF signal (which it shouldn't) there shouldn't be anything for the FCC to type accept. Your example of headphones was pretty good, but how about one step further--I have Ham and FRS radios with speaker mics that are able to key-up the TX. AFAIK, none of them are type accepted.

Nathan

tadawson

I think you will be fine. The issue is the RF desk and it's interface to the radio. Going in via a DSC CORD (chord is in music . . . ) does not change this interface - it will ultimately give a different set of control signals to the RF deck, but the interface in the radio will still determine the signal level and thus deviation of the RF deck. To the comments by apteryx, the signal level to an FM transmitter is just as crucial to bandwidth, if not more so that in AM - since the singnal strength into an FM transmitter determines frequency shift, to high a level will violate the narrow band specs in a hurry. On AM, if the singnal in is always "clean", you won't go out of band by increasing signal level until the transmitter starts to clip (being driven beyond it's power capacity" and then it goes really ugly really fast - not just wider, but all over the map.

- Tim

mr.rc-cam

You'll be fine if you interface to the trainer port and do not modify the host Tx.

Bax

My Feedback: (11)

You must remember that with R/C transmitters in the Radio Control Service, the only information allowed to be transmitted is that needed to control the devices plugged into the receiver (servos, gyros, speed controls, stability-augmentation devices, etc). Other types of information cannot be transmitted. In other words, only the information from the sticks and other controls on the transmitter.

For example, if you build a computer-controlled autopilot, you cannot use an R/C transmitter to send information on where it's supposed to fly. You can send "left", "right", "up", "down" information, but not something like "fly at 400 feet to location Y".

You can send information to advance, retard, or hold the throttle postion, but not tell the onboard equipment to run the engine at a specific RPM. This may seem contrary to the use of governors in helis, but the controls from the transmitter only tell the governor to select one of the governed speeds preset into the unit. Specific RPM information is not transmitted.

bax

Lynx

Bax, can you point out the FCC rules that show that?

apteryx

Part 95.631 (f) "No GMRS, CB, or R/C transmitter shall transmit non-voice data". (b) "An R/C transmitter may transmit any appropriate non-voice emission which meets the emission limitations of Sec 95.633".

That's not really in conflict because "appropriate emission" means just like Bax says. Sec 95.633 has to do with emission bandwidth.

On a previous point about AM/FM, the "FM" transmitters I have are really not the classic "FM emission" they are really "FM FSK" transmitters.

tadawson

Actually, on most of the current govs, including the Futaba GV-1, you can continuously vary the speed, and as such, determine how to command a specific speed, not just a preset. The new throttle jockey govenrnor is programmed by calculating what value needs to be sent from the TX to the gov to give a given speed. Put it on a pot, stick a label on it, and it seems a lot like what you describe . . . .

????

- Tim

Lynx

Thank you folks that's what I thought, I thought BAX was on crack for a few seconds there.

Bax

My Feedback: (11)

That's not the same thing as having the transmitter send specific information. What you're doing is sending relative position information. If you just happen to mark the transmitter knob or switch to indicate where you've got the device set, you're not really sending specific data to the model. The telemetry information would be having the transmitter specifically send the governor to maintain 1,700 RPM on the main rotor. You'd be inputting the RPM into the transmitter, and then it would send that data to the receiver and the goveror. In the case of existing equipment, you're basically finding out which knob (or stick) position gives you the desired performance and then marking that on the Tx so that you can repeat it. The transmitter's not actually sending anything other than relative position information. You've just marked the Tx to make it easy to locate that particular relative position.

Bax

My Feedback: (11)

Here's where the FCC has the basic definition of the Radio Control Service. Please note that it states that data is not allowed to be transmitted.

http://wireless.fcc.gov/services/personal/radiocontrol/

tadawson

It would be interesting to see how they define "data", since every definition I can think of would call the PCM stream digital DATA of encoded positions.

???

- Tim

mr.rc-cam

From what I understand, "data" would be any communication that involved information transmission rather than DIRECT model control signaling. The Part 95 rules prevent sending telemetry-like info using R/C model frequencies. The license-free R/C freq spectrum is reserved for model control only (exceptions are in place for licensed heavy equipment control and license-free auditory assistance devices).

You can use any format to remotely control a hobby type model aircraft, car, etc -- even digital "data" is allowed. The basic restrictions involve RF power, freq, spectral bandwidth, and intended application (must be hobby model control).

Lynx

That's okay, the 'operator turning on or off a device at a remote location' provides a simple loophole. You just require that before the device is turned on and active that configuration information, in which case you might be sending data, but it's just a complex form of an 'on' command. It's all very vague and sidewinding typical FCC stuff. Doesn't matter anyways, any telemetry or 'data' I wish to transmit will be done on frequencies legal to do so, that was never an issue to me. It's just the interception and modification of the PPM frame that interests me.

tadawson

I was just thinking here, Bax made a comment along the lines of "is not the same as a signal commanding a given position or speed." or some such. Once again, I question how this is compatible with current PCM systems. The PCM systems sends a specific digital DATA frame with an EXPLICIT value commanding an EXPLICIT servo position. I can see not sending telemetry, but commanding a given head speed is not telemetry - it is flight control in a more exact manner, and I question whether that would be truly against the regs or not, or if Bax is taking the ultra-conservative route that will never get you in trouble, but may not actually be totally accurate either.

- Tim

Lynx

Clasically, technically, and legally speaking. Even PPM is 'telemetry' Modern Radio Control signals are more than on/off so aren't covered by The Radio Control Radio Service PERIOD. I need FCC reg's not third party links. I'm serious not a 'weekender' I've been working on this idea for almost a year now, I think I deserve better than such a tertiary responces.

Bax

My Feedback: (11)

Everything you need is in CFR 47 Part 95. You can access this at:

http://www.fcc.gov

For exact technical information, you'll have to discuss your proposal with the Technical Branch of the FCC. They'll be able to give you a definitive answer.

Mluvara

My Feedback: (10)

These may helpful.

http://a257.g.akamaitech.net/7/257/2...7cfr95.211.pdf
http://a257.g.akamaitech.net/7/257/2...7cfr95.212.pdf

R/C is for one way communications only. Telemetry would generally mean that you are transmitting back to obtain information and then command back to the aircraft. Those that are doing both have migrated to other bands.

Michael