Thanks Kevin, Now I know the reason for the offset. tom
On 6/24/2010 4:58 PM, Kevin Custer wrote: > Jeff DePolo wrote: > >> To get the RF phase accuracy you're implying that is required would mean >> that everything in the RF path would have to guarantee that phase >> relationship. That means the same length RF interconnect cables inside the >> cabinet, same RF feedline length (or full-wavelength multiples thereof), >> same antenna type, etc. Even if you could guarantee that kind of accuracy >> at the time of installation, thermal effects would quickly throw it way off >> (cables expanding/contracting with temperature for example). Not to mention >> the propagation delay will vary a whole lot with temperature, humidity, etc. >> Just not gotta happen.... >> > > And in practice, we know it isn't going to happen, so we purposely set > the frequency difference between transmitters that overlap in coverage > to about 20 Hz. This negates most negative effects of two transmitters > being real close but not dead on frequency or angle. > Transmitters that are very close to one another will cause PL tone > decoders in the users radio to not reliably open, not to mention to > weird audio artifacts that are produced/heard. At 20 Hertz, or so, > CTCSS tone decoders work fine and radios' speakers don't emit a horrible > beat note. > > Kevin > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > >
