Re: Want to mix american and european styled Lectros.

Larry,

I throughly enjoyed this post. But,I had a good chuckle as my wife, who
has been in the medical profession for almost 30 year, had her eyes gloss
over as she tried to read it. After finishing it, her only response was,
"HUH?".

David White
"Larry Fisher" <lectrosonics@xxxxxxxxx> wrote in message
news:u24m245867uq2n89ra13roih3j7qosl08k@xxxxxxxxxx
Hi Rich,
Sorry this took so long but I went ahead and did an FAQ #122.
http://lectrosonics.com/faq/faq1byref.php?id=122

Q: What are the advantages of 75 kHz deviation as allowed in the US
versus the narrower 50 kHz (or less) deviation allowed in Europe and
some other parts of the world?

A: Deviation is the measure of how far a frequency modulated RF
carrier can change frequency in response to a signal such as audio.
The amount of deviation is limited to a maximum value by regulatory
agencies or it can be limited to a maximum bandwidth that the signal
can occupy centered on the carrier frequency. For instance, the FCC
specifies a 75 kHz peak deviation and a maximum occupied bandwidth of
200 kHz.

FM is a form of spread spectrum modulation since the occupied
bandwidth is greater than the bandwidth of the audio signal. For
instance, at full modulation, a 1 kHz test tone broadcast by an AM
station would occupy a little over 2 kHz of bandwidth but as wideband
FM modulation it occupies more than 150 kHz of bandwidth. This
additional occupied bandwidth has "process gain" just like any spread
spectrum signal and suppresses interfering signals and noise. The
greater the deviation, the greater the noise suppression effect. In
general, 75 kHz deviation systems have over 3 dB better noise
performance than 50 kHz systems, all other things being equal. With a
compander in the system, the 3 dB RF link improvement due to the wider
deviation sounds like a 6 dB improvement to the ear. There is a
downside to the wider deviation and that is at very low levels of RF,
the wider deviation loses its advantage over the narrower deviation
systems and actually has a disadvantage. However, this occurs only
when audio signal to noise ratios are at 12 dB or lower, which is
effectively useless for wireless microphone purposes anyway.

Best Regards,
Larry Fisher
Lectrosonics

On Thu, 8 May 2008 14:43:47 -0700 (PDT), rich
<calumide-fiction@xxxxxxxxxxx> wrote:

HI Larry. just curious what difference does the deviation make? does
it affect range or audio?
thanks
rich


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