[NSRCA-discussion] RX choices

[Ken Thompson]

John,

We have the "need for speed", but not around center.;-)

Ken
----- Original Message ----- 
From: "John Pavlick" <jpavlick at idseng.com>
To: "NSRCA Mailing List" <nsrca-discussion at lists.nsrca.org>
Sent: Friday, September 15, 2006 12:49 AM
Subject: Re: [NSRCA-discussion] RX choices


> 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
>
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