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DPRG: Linx RF Modules

Subject: DPRG: Linx RF Modules
From: Douglas Kilgore dougkilgore at home.com
Date: Wed Nov 10 11:37:12 CST 1999

300 Mhz  -  400 Mhz  -  900 Mhz  ----     The higher the frequency, the more
important the circuit and antenna design become.  The Linx modules generate the
signals but the board that that the modules plug into actually gets the RF signal
to the outside world.  The reason they insist on selling an evaluation kit is that
they have designed the a successful interface between the modules and antenna.
Otherwise the buyer would have to go thru a design and test phase before even
attempting to evaluate their RF modules.

The Linx LC modules us AM modulation which is more susceptable to static noise.
The RM series uses FM Frequency Shift Keying (FSK) which due to it's "capture" of
the signal is less susceptable to static noise.  Ham radio operators have been
using 1200 baud FSK FM for packet radio for years using just using their 144 and
440 Mhz narrow band radios.  The use of higher speed in becoming more prevalent.
Everything that you wanted to know about data transmission over RF but was afraid
to ask can be found at www.tapr.org.

A word to the wise - the 900 Mhz band is very crowded in the Dallas and other big
city areas.  Remember you are using a very low power Part 15 module.  There are
phones, truck radio dispatch, etc.  I one bought a 900 Mhz Part 15 FM wireless
microphone with 4 frequencies to use in a video business.  It would work only
intermittently.  Had to send it back.  The manufacturer checked it out and said it
was working.  Later I tuned into the 900 Mhz band with my ham radio and heard how
crowded it was.  My theory  was that because of the capture effect, the wireless
mike receiver would lock onto another stronger signal which wasn't mine.  The
system used a subaudible tone to break the squelch and when it didn't get it, it
kept the audio off..

 Read all of the Linx tech notes before buying.  They are good.

Doug Kilgore KD5OUG


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