Radio Modulation
 

Why is FM better than AM, why is PPM better than FM, why is PCM better than PPM?????
i need help. and what is 1024 PCM
does it really make a differance

RE: Radio Modulation
 

Well lets see, PPM and PCM are both FM. The benefit of PPM to PCM is PCM has noise rejection and fail safe. FM is better at rejecting noise spikes than AM.

RE: Radio Modulation
 

That says it in a nutshell.
Dennis-

RE: Radio Modulation
 

Check this out:

http://www.torreypinesgulls.org/Radios.htm

Jesse

RE: Radio Modulation
 

Since somebody posted about the Fm then i would like an answer,how many watts does most of the tx's put out ?.
Thanks

RE: Radio Modulation
 

WE have AMA and FM... no other frequency modulaton.

Keeping it SIMPLISTIC... (someone could write an explaination that takes a CD to hold all the information...)

PPM and PCM are the signal encoding sent by the modulation. Its kind of like... do you want to send a digital computer signal or just send the same music in the form of the common AM radio waves. you can do either with AM or FM radio. (thats a simplistic explaination of the difference between AM radio and some early AM wireless networks...)

FM does inherantly have some improved interference rejection simply because the radio is chcking a "range" of frequencys for changes in a constant power level but varying the frequency. AM varies the power of the radi wave transmitted. and that closely resembles the noise generated by power lines. (thats basicly why AM radios go nuts under the high tension power lines... but FM you continue to hear your music.)


PPM - Pulse Proportional Modulation. if you have the correct type oscilliscope... you can LOOK at the signal and you will see the signal pattern and you can SEE the stick positions.

PCM - Pulse Code Modultaion. You have a seeries of digital codes being sent... the signal would look the same if you were sending a repeating binary computer code. just 1's and zeros. You can't see the stick positions unless you can decipher the code in your head.

RE: Radio Modulation
 

I suspect between 1/4 to 1/2 watt.

RE: Radio Modulation
 

You can look it up in the CFR part 95 and 97 regs. (the Radio Control section of the FCC rules) The maximum allowed is essentially right where the manufacturers all shoot for.

http://frwebgate3.access.gpo.gov/cgi...ction=retrieve

Too much legaleese for me to want to dig through it right now...:eek:

*******************

Well... OK I dug:eek: was easy to find using search on the section number from the table of contents.

Sec. 95.210 (R/C Rule 10) How much power may I use?

(a) Your R/C station transmitter power output must not exceed the
following value under any conditions:

------------------------------------------------------------------------
Transmitter
power
Channel (carrier
power)
(watts)
------------------------------------------------------------------------
27.255 MHz............................................... .. 25
26.995-27.195 MHz.......................................... 4
72-76 MHz............................................... ... 0.75
------------------------------------------------------------------------

(b) Use of a transmitter which has power output in excess of that
authorized voids your authority to operate the station.

*************

Not sure why the formatting is maintained in the edit message box and not in the posted message. somethings goofy. (must be "tabs" in the text I copied... and the system is deleting them.)

RE: Radio Modulation
 

PPM = Pulse "Position" Modulation and not "proportional", just to add something.

Just to know, of course there are advantages of AM-Amplitude modulation, otherwise there would be no AM radios anymore.
Considering that no satelites are available to everyone, AM is the way to modulate low frequency carriers, that means long wave lengh that reach much farther than high frequency carriers. FM is applied over relatively high frequencies (HF and up = 30Mhz and up) with good performance.
You can listen to AM radios from everywhere in the planet, without good quality and reliability, but works.
For RC and anything that needs to be reliable, Didital modulation of course is the better option, noise rejection, multiple digital channels and features.
The future however is CDMA (code division multiple access) that already works for a long time for the military and lately for Celular networks and hopefully will come to RC one day. This process will allow all pilots to transmitt at the same frequency, side by side, and have their planes just under control. On CDMA spread spectrum, each user have a unique "digital" code that makes the miracle. No cristals or frequency boads anymore!

Note.: Currently, the CDMA cellular phone networks allows up to 64 user to talk at the same frequency, at the same time.

Nilo

RE: Radio Modulation
 

thanks fot he help guys