here is a better diagram http://murray.newcastle.edu.au/users/staff/eemf/ELEC351/SProjects/Morris/typ es.htm#hybrid Jonathan -----Original Message----- From: Jonathan Johnson [mailto:jonathan@outeredge.net] Sent: Thursday, 31 October 2002 11:11 AM To: pic microcontroller discussion list Subject: RE: [EE]: Spread Spectrum systems > -----Original Message----- > From: pic microcontroller discussion list > [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Dave Tweed > Sent: Thursday, 31 October 2002 2:57 AM > To: PICLIST@MITVMA.MIT.EDU > Subject: Re: [EE]: Spread Spectrum systems > > > Jim wrote: > > "Jonathan Johnson" wrote: > > > Has anyone had any experience or know anything about hybrid Direct > > > sequence/Frequency Hopping spread spectrum systems? > > > > Firstly, SS does not equal 'frequency hopping'. > > As the OP already indicated, spread spectrum can be either direct sequence > (as used in GPS) or frequency hopping (as used by hams in the VHF bands). > There is also something called "chirp spreading", but this is rare. > What is Chirp spreading? Is it something like sweeping the carrier frequency instead of hopping or gaussian spreading it? > > The key to this is: look at the differences in the bandwidths of the IF > > filters used in each ... > > Before or after de-spreading? > > > > I'm curious as to how big the spread width would be for a given number > > > of frequency hops, is it better to have more hops or a wider spread, > > With frequency-hopping, the "spread width" is simply a matter of the > difference between the lowest frequency you use and the highest. Choosing > the hop rate and the number of carrier frequencies you use is a > combination > of what frequencies you're licensed to use, how good your frequency-agile > oscillator is, and how well your receiver synchronizer works. > What I was really proposing was something along the lines of the little diagram below: hop1 _hop2 _hop3 _hop4 _hop5 _hop6 *******_*******_*******_*******_*******_******* in this diagram the number of hops or carriers is 6 and the DS spread width is 7*, a '*' is just a unit of bandwidth for example so to occupy the same bandwidth, is it better to have: hop1_hop2_hop3_hop4_hop5_hop6_hop7_hop8_hop9_hop10 ****-****-****-****-****-****-****-****-****-**** where hops or carriers = 10 DS spread width = 4 total bandwidth = 10 x 4 = 40 units of bandwidth or hop1 - hop2 - hop3 - hop4 - hop5 ********-********-********-********-******** where hops or carriers = 5 DS spread width = 8 total bandwidth =5 x 8 =40 units of bandwidth > The ARRL Spread Spectrum Sourcebook is a good reference to get > you started. > thanks Dave I'll check that one out. Best Regards Jonathan -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics