different type of moudulation

[blurchaoz]

hi everyone,

need to clarify on some matters here about the modulation. im pretty confused about PPM, PCM, SPCM, QPCM, ZPCM. can someone help me find a url that explains the difference of this 5 different modulation.
thanks for the help in advance guys. . .

[mathsinstrument]

hi everyone,

need to clarify on some matters here about the modulation. im pretty confused about PPM, PCM, SPCM, QPCM, ZPCM. can someone help me find a url that explains the difference of this 5 different modulation.
thanks for the help in advance guys. . .

Ok... First you need to understand what is FM first. FM stands for frequency modulation. AM which is Amplitude modulation.
Why FM is more superior than AM? FM is less susceptible to noise and there's this effect (i forgotten the term for it) which allows it so block off 90% of the interfering signals (ie. AM of the same frequency, FM with frequency close to yours). That's why when a AM of the same frequency band as you, your FM TX might still function as it is.
PPM, PCM, SPCM, QPCM, ZPCM??? are all different techniques of modulation from FM.

PPM = Pulse Position Modulation.
PCM = Pulse Code Modulation.
SPCM =
QPCM = Quatre Pulse Code Modulation
ZPCM = ???

I haven really read up on some of the frequency modulation techniques and there are new one everyday, so basically, the below is what i know.

The most basic frequency modulation technique used is PCM. It's good and reliable.
PPM is a variation of PCM. It takes a bit more power, so it can transmit further.
QPCM is much more efficient than PCM because, it is quarter the size of PCM(hence it's name). But the down point is more expensive receiver to demodulate the signals(more electronics found in the reciever). But it gives clearer and cleaner signals and lower noise to signal ratio.

There's more to it, but if you want to know further then let me know. I will post it up.
By the way, I did this for my poly project!! Hobby and school project has never gotten betta.....

[mathsinstrument]

FM ==> All
PCM ==> Popular models all come with
QPCM ==> Hitec
ZPCM/SPCM ==> Futaba and JR(Mainly JR)
PPM ==> Most models also got PPM

still got many more eg. PWM, PAM ePCM etc......
Depending on the chip the manufacturer want to use, PCM being the cheapest to implement, so most popular models all got PCM.
PCM got failsafe because got a 512bytes memory inside to store the last position. That memory is SRAM.

But getting a radio also depends on other factors like the step resolution, frequency shift(Doppler shifting), pulse code keying and etc.....

[Artyspec]

correct me if i am wrong but i think PPM is the one which every transmiter has. and QPCM,SPCM,PCM are different brands of PCM. I can confirm PCM is for Futaba. SPCM is for JR if i am not wrong and QPCM is for Hitec. They are all propietary. PCM tends to have less glitches(from my experience) and i guess it transmits further? I think PPM is the one which is cheap to implement as most cheap radios like GWS and Laser 4 etc. all have PPM only.

just my 2 cents

[mathsinstrument]

correct me if i am wrong but i think PPM is the one which every transmiter has. and QPCM,SPCM,PCM are different brands of PCM. I can confirm PCM is for Futaba. SPCM is for JR if i am not wrong and QPCM is for Hitec. They are all propietary. PCM tends to have less glitches(from my experience) and i guess it transmits further? I think PPM is the one which is cheap to implement as most cheap radios like GWS and Laser 4 etc. all have PPM only.

just my 2 cents

I'm not sure about the current prices of the chips which are available in the market. But the receivers are expensive due to the band-pass filters and in the case of PCM, the added memory for the implementation of the failsafe(my lecturer used to fly nitro planes ).
As a matter of fact, PPM and PCM are somewhat on the same level. PCM was the first standard FM implementation by some international organisation. PPM is a variation of PCM. Just like as in QPCM, SPCM, ZPCM etc.....
If the PPM is properly manufactured using the right channel spacing and calibration of the channel bandwidth, THEORTICALLY, should some how be better than PCM.
TECHNICALLY, i never try before.... All the while use PCM nia....

[mathsinstrument]

Sorry for the mis guided infomation. PPM is lousier than PCM. It should be the other way round. PPM was first, then PCM.

[mathsinstrument]

Found my project:

Here's the report for PCM summarised:
In the PCM controller, microprocessors are embedded into both the transmitter and receiver to encode and decode the signals transmitted from the TX to the RX. These microprocessors handles bulk of the conversion and the frame relay to the servos thus, giving the RX the small footprint.

[mathsinstrument]

I believe this will be useful for pple who wanna buy a new radio:

Z-PCM: JR/Granuper
The first generation of PCM developed by Japan Radio and Granuper. It is also known as PCM interlacing, which uses 2 half channels for uplink and down link, mimicing the same feature which uses a full duplex single channel for uplink and downlink.
Servo Accuracy 2^9 = 512

S-PCM: JR/Granupner
2nd generation of PCM developed by the them. It has higher accuracy rate than the Z-PCM
Servo Accuracy 2^10 = 1024

PCM 1024: Futaba/Robbe
Developed by Futaba and Robbe, the PCM 1024 is the fastest in comparsion. It has the fastest framerate. Differential encoding structure allows the number of bits transmitted per frame to be reduced from 20 to 14.
The first frame contains the position, while the consecutive frames sent are just corrective frames. It does not require to send the entire frame again.
Servo Accuracy 2^10=1024

I-PD PPM: Multiplex
Intelligent Pulse Decoding Pulse Position Modulation.
Developed by mulitplex for use with the royal radios. Improved version of PPM which allows more efficient use of bandwidth of the PPM.
Servo Accuracy 2^9=512

*Servo accuracy = The number of bits sent in a single frame. 60 degree angle, the number of steps/positions of the servo within that range.