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PCM 1024 System Info

So that you may be better able to understand and appreciate the Futaba PCM 1024 systems, in particular the 9Z WC2 transmitters, let us discuss a few radio control system fundamentals in general and those of PCM in particular.

Wave forms

Some misconceptions seem to exist regarding PCM (Pulse Code Modulation) systems, it being believed that it is a brand new method of signal transmission, similar to AM and FM.

Not so! PCM is a highly advanced method of encoding, having capabilities in common with other signal transmission systems, and first developed and introduced to the radio control world by Futaba technology.

Let us take first things first. We can generate a radio frequency signal, a wave, which has the ability to travel through free space. By itself, it can be detected within a receiver, but can do little else. However, this RF signal can do more work by making it carry information with a process known as "modulation." Any basic signal, regardless of frequency, can be modulated to bring you voice, music, "pictures at eleven," or even R/C control information. There are numerous modulation techniques, of which two are commonly used in radio control transmitters. The favored ones are: AM-Amplified Modulation, which modifies the RF signal by varying its strength, or amplitude, and FM-Frequency Modulation, which does so by deviating a small amount from the basic or center frequency. You may have read of others, with impressive sounding names but they are all merely variations of one of the above.

In a voice or music system there is usually no encoding as such, though the recently introduced digital audio systems actually use a type of PCM. The highs and lows of the sound ultimately produce the same effect in the amplitude in an AM system, or the frequency in an FM one, of the RF output. However, in the R/C transmitter, the physical stick movements must first be converted into their precise electrical counterparts. That is done by circuitry called an "encoder." As you might expect, at the receiving end, the information is extracted and used to drive the servos by a circuit called a "decoder." As you can see from our block diagram up above, the sequence starts with the encoder, whose output goes to the modulator, in turn to the RF amplifier, to be transmitted to the receiver.

The very first R/C encoder was a button on the transmitter that one pushed to make the rudder move. Those of you who were flying in that era will surely appreciate today's precision and sophistication much more than the younger crowd. Starting with those humble push buttons, a number of different encoding methods were used in the early days, but eventually, a system using a pulse of varying length to control servo position was evolved. It worked well and was eventually perfected and accepted as the standard for radio control transmission by all makers. That system, now know as PPM (Pulse Position Modulation), is still in use in most R/C systems flying today.

Modulation diagram

However, time marches on, and the time came when R/C model development demanded a more advanced control system, which at the same time would take advantage of all modern applicable electronic component and circuit advancements. Thus the first PCM, the Futaba 8-channel 512 system was born! PCM encoding, the most precise system yet developed, converts all physical transmitter control inputs into "bits," an acronym meaning binary digits, the unit upon which all modern computer technology is based.

The heart of any computer, or any item based on computer technology, is an IC (Integrated Circuit), called a "microprocessor." The microprocessor, being a true electronic brain, is what make today's unbelievably capable computers possible, and such a device, designed specifically to provide the functions required for a fully optimized R/C transmitter, is what make the 9Z WC2 transmitters possible.

Once generated, any encoded output can be used to modulate the RF signal in either the AM or FM mode. However, since extensive testing has proven the superiority of the FM/PCM combination, all Futaba PCM systems utilize FM as the transmission medium. Additionally, to further increase the versatility of the 1024 systems, the transmitters can also be used in the older, but still useful, PPM transmission mode. This requires only the flick of a switch, and none of the many other 9VA/9VH features are lost or reduced. This allows use of the transmitter with already owned Futaba non-PCM receivers, or with less expensive units for those not too demanding sport flying applications.


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