[NSRCA-discussion] RX choices

[John Pavlick]

Jim,
 The heli guys can feel the difference between the "old" Futaba 1024 PCM and
the new G3 - or so I'm told. One of my friends just got a 14Mz and said he
had some interesting moments with his Rap 90 until he got used to it (the
2048 PCM with fast frame-rate). I'm still amazed at how we use fast digital
servos, then add expo to soften them up. I know there's more to it than that
but it seems kind of silly in a way.

John Pavlick
http://www.idseng.com


> -----Original Message-----
> From: nsrca-discussion-bounces at lists.nsrca.org
> [mailto:nsrca-discussion-bounces at lists.nsrca.org]On Behalf Of J.Oddino
> Sent: Friday, September 15, 2006 12:32 AM
> To: NSRCA Mailing List
> Subject: Re: [NSRCA-discussion] RX choices
>
>
> PCM works better than PPM when both are working.  When you receive a good
> frame of PCM it is perfect, that is, it is exactly what was
> encoded.  PPM is
> always corrupted by the RF link.  RF noise shows up as pulse jitter in the
> decoded signal.  This is usually only noticed when the signal to noise is
> low as it might be at long range with bad antenna orientation.  This was
> very apparent in the PPM-AM systems that proceeded PPM-FM.
>
> The PCM system only has to decide it there is a pulse present or not.  The
> PPM system must accurately measure the time between pulses.  This is easy
> with nice square pulses but impossible with distorted rounded pulses.  The
> net result is the PCM will work better and this is easy to demonstrate at
> max range.
>
> The Berg and Multiplex receivers that use Digital Signal
> Processors minimize
> the jitter by essentially filtering the PPM signal.  I'm not sure of the
> algorithms used but typically filtering adds a delay.  Apparently
> it is too
> small to be detected by RC pattern pilots.  It would be
> interesting to know
> if the heli guys can detect it.
>
> Jim O

--
No virus found in this outgoing message.
Checked by AVG Free Edition.
Version: 7.1.405 / Virus Database: 268.12.4/448 - Release Date: 9/14/06