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From: darel@maccs.dcss.mcmaster.ca (Darel Mesher)
Newsgroups: sci.electronics
Subject: Re: Looking for FM transmitter
Message-ID: <266D40A5.4146@maccs.dcss.mcmaster.ca>
Date: 6 Jun 90 17:42:59 GMT
References: <27510002@hpcvia.CV.HP.COM> <61340@sgi.sgi.com>
Organization: McMaster University, Hamilton, Ontario, Canada
Lines: 49

In article <61340@sgi.sgi.com> rpw3@sgi.com (Rob Warnock) writes:
>In article <27510002@hpcvia.CV.HP.COM> jayer@hpcvia.CV.HP.COM
>(Jay_Reinhart) writes:
>+---------------
>| I am looking for sources for a good wireless FM transmitter that is fairly
>| low cost. I need one that is small enough to fit inside a motorcycle helmet.
>| Or if it is cheaper I could just run the mike into the helmet and carry
>| the transmitter.
>+---------------
>
>Radio-Shack has a new version of their 49 MHz walkie-talkie that uses a
>combined earplug/mic, the kind that picks up your voice *out* through your
>ear. The actual transceiver is in a little box that mounts on a belt clip.
>The wire between is also the antenna.
>

   I had to respond to this one..... don't buy these units with the interest
of using them on motorcyles!

   i) the units are very susceptible to engine noise radiated at such close
	distances (ie. spark plugs only a few feet away)
  ii) the units require a separation between the two units for proper 
	operation, the spurious radiation from the units themselves 
	interfere with normal VOX operation. If both the driver and 
	passenger are using the units and one unit xmits, the other unit
	will toggle into xmit mode ..therefore neither unit can receive, 
	and they will remain in xmit mode until manually switched out of
	VOX.
  iii) Finally... you must also realize the there are a KaZillion Fisher
	Price baby monitors out there, each on 49Mhz and each broadcasting
	for miles and miles and miles.....  Last year on a bike trip out
	east my wife and I were absolutely amazed at the conversations we
	were party to because of the RS headsets we were wearing. Every time
	we entered a city limits the VOX would kick in and then we would 
	get to listen to crying, baby-talk, family fights...... I'll tell
	you, the FBI sure doesn't need to bug houses anymore- just use
	a baby-monitor-monitor!

 So, spend the little extra and buy headsets actually designed for motorcycle
use! (as a side note, I immediately took the units apart to see if I could
desensitive/detune the units for close proximity use to no avail; unmarked 
hybrid parts with few tunable components!)

Darel
-- 
=============================================================================
Darel Mesher			
Electrical and Computer Engineering
McMaster University			    darel@maccs.dcss.mcmaster.ca