For the record, I am not an Engineer or involved in this industry. I have done lots of research on this subject. I compile data and regurgitate my understanding in my responses. I have several sources close to the industry that I rely on for technical information and understanding.
Mglavin. What does single conversion vs. dual conversion have to do with Pulse Position Modulation (analog) vs. Pulse Code Modulation?
Nothing. I was simply noting that these were included in my ramblings.
All the information you just provided is correct for rejecting unwanted rf signals near, or at the center frequency as a result of mixing (harmonics). All this is fine and dandy when one needs to consider rf sources such as cranes, other hobby transmitters, etc.
These sources however are not the root of our problems. The source most likely to interfere with our models almost always eminates from within the model itself. The source is noise, of a very high level in close proximity to the reciever.
I’m not sure why you’re suggesting these problems are not the “root”, these scenarios exist and are problematic. How does one quantify “most likely”?
The most common source is either conducted emi (transients, loose connections, bad servos, or poor radio installation, inadequate wire gauge, etc.) or radiated emi.
This maybe true but I suspect it’s an assumption. A properly rigged and operating model will not have these attributes, albeit it’s a plausible occurrence and may also be a common scenario. RFI can and will present itself; I believe it’s more common than EMI in the day to day use of our models. Therefore the aforementioned information has merit. I’ll stick my head out and suggest this information is generic to the either RFI and or EMI.
Wouldn’t attempting to distinguish the difference between RFI and EMI be a rather lofty adventure? Isn’t noise, noise? Does an RC RX know the difference?
Radiated is far more likely to come from within the aircraft itself than anywhere else.
I concur.
Metal to metal abrasion is one such source.
Whoops, I forgot to mention radiated ignition noise.........
Either of these two sources interferes with both types of recievers.
Again, I concur.
The attributes you describe previously, 3IMG, etc. are shared attributes between both PPM and PCM recievers, and frankly I'm not sure what you're point is bringing that up.
3IM is most definitely a required and or wanted and shared attribute of either AM/FM PPM or PCM RX’s.
You're confusing matters. Why bring up image rejection, and the like? What's that have to do with anything?
What happens when two signals appropriately spaced enter the 1st mixer? The RX must be able to reject these two signals by a calculated factor higher than the received controlling channel. Two similar signals are injected during test’s, thus my reference.
Ill informed, perhaps. I've yet to see any published hard facts. All I've seen thus far are assertions by you, and your ilk.
My assertions are for discussion, it’s not my intention to be a condescending or lofty. I provide the reasoning for such and it’s up to the individual reading the information to determine one way or the other.
Now lest you believe that I'm arguing in favor of one scheme over the other, let me state that I'm not. I simply haven't seen anything to sway me one way or the other.
I hear where you’re coming from; based on your comments I assumed you were in favor of the PPM scheme.
As for the aforementioned tests. You neglect to say who/whom conducted these tests, and for what puposes. Were they range testing for loss of signal, or did they have defined signal sources of interference by which they could establish the thresholds whereby 'loss' of signal occurs? All this kind of "internet" information makes me skeptical.
The tests I am aware of were performed by several individuals and hobbyists in the industry.
Once values could be placed on what an RC model sees, tests of interference could be recorded simulating real world field conditions for evaluation purposes. Defined signal sources and thresholds were employed.
One could look at testing RC RX’s from several levels, BUT what really is the tell all is the control signal the servos actually see, If we can establish what dB level is required to cause servo jitter (+/- 40 us) we have a method that suggests which scheme is superior. Could it be any simpler?
Should have some new test data tomorrow afternoon. Were going to use Futaba RX's specifically and hopefully some JR equipment if I can round some up.