These modes use interleaving and randomize data values by exclusive-ORing with
a pseudorandom binary sequence. The methods are used in most commerial products
and the FCC and NSA know how to monitor the signals.
The FCCs problem is that the military uses FHSS and DSSS to hide the existance
and content of their transmissions thus preventing the monitoring that the FCC
is required to do of amateur signals. It took AMRAD a long time to get
authorization for SS above 222 MHz. They first had to get experimental licenses
for test transmissions and satisfy the FCC that they could monitor the signals.
73,
John
KD6OZH
----- Original Message -----
From: Rik van Riel
To: digitalradio@yahoogroups.com
Sent: Wednesday, February 24, 2010 02:32 UTC
Subject: Re: [digitalradio] Consensus? Is ROS Legal in US?`
On 02/23/2010 09:00 PM, KH6TY wrote:
> The distinguishing characteristic of spread spectrum is spreading by a
> code INDEPENDENT of the data. FM for example, creates carriers depending
> upon the audio frequency and amplitude. SSB creates carriers at a
> frequency dependent upon the tone frequency, and RTTY at a pair of set
> frequencirs depending upon the shift or the tones used to generate
> shift. In spread spectrum, as Jose has written, an independent code is
> used for the spreading, one of the requirements to classify it as spread
> spectrum.
One of the requirements - not the single determining
characteristic by any means.
From a quick look through the fldigi source code,
MFSK and Olivia appear to use a pseudo-random code
as well, to provide robustness against narrow band
interference.
From several places in src/include/jalocha/pj_mfsk.h
static const uint64_t ScramblingCode = 0xE257E6D0291574ECLL;
--
All rights reversed.
