From: "Phil Allison"
References: <3DE7415A.A4A4F74C@sympatico.ca> <3DE93B11.915657D1@sympatico.ca>
Subject: Re: Detecting moment when a fast moving object passes over a line
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Sun, 1 Dec 2002 09:33:01 +1100
NNTP-Posting-Date: Sun, 01 Dec 2002 09:22:24 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"Gerry Schneider" wrote in message
> Phil Allison wrote:
> > "Gerry Schneider" wrote in message
> > news:3DE7415A.A4A4F74C@sympatico.ca...
> > >
> > > Without getting involved in any on-going arguments about terminology
> > and/or
> > > expertise, maybe I can just just mention a few points.
> > >
> > > An AM receiver of the 418/433MHz variety won't work in close proximity
> > an
> > > electric RC motor,
> > ** Huh? Ones on 27, 29, 36, 40, 70, 75 MHz work fine.
> 418/433 transmit power is extremely limted - about 1 mW - compared to
> of mW for the R/C frequencies you mention, so the Rx is trying to detect a
> signal in the presence of strong interference.
** Where is the "strong interference" coming from?? Simple supression
methods work well for 27 to 75 Mhz RC gear. The higher the frequency the
less RF energy is radiated from a small motor - IME. BTW In the OP's
proposed system the Rx will be trackside.
Also, 418/433 Tx frequency is
> either LC or SAW controlled, so the Rx passband needs to be either very
> (superregen) or moderately wide (SAW superhet).
** Can you put a figure on this - sounds evil.
BTW the RF stage bandwidth of a typical RC radio is about 2 - 3 % of
the centre frequency to allow for drift and crystal changing.