And there is the issue of PL tone. Keep dropping the modulation level and decoding becomes tougher, at least with boards like ComSpec.
Chuck WB2EDV ----- Original Message ----- From: "wb6dgn" <wb6...@att.net> To: <Repeater-Builder@yahoogroups.com> Sent: Friday, August 27, 2010 11:43 PM Subject: [Repeater-Builder] Re: Narrowband Range -was- Seeking emergency system design help OK. But with that kind of "micro" modulation, you're going to be dealing with problems more difficult to solve than frequency stability, though I agree that would be one of them. Tom --- In Repeater-Builder@yahoogroups.com, DCFluX <dcf...@...> wrote: > > I was talking about 1kHz and 100 Hz deviation, not 2.5kHz. > > On Fri, Aug 27, 2010 at 8:30 PM, wb6dgn <wb6...@...> wrote: > > "As receiver bandwidth narrows, higher frequency stability is required. > > Handhelds with ovenized reference oscillators are not very practical." > > > > TCXOs are more than adequate to do the job. Typical frequency stability > > for a +-5.0kC system is 5ppm. TCXOs of 0.5ppm are common and not > > terribly expensive; more than 2.5 times more stable than conventional > > wisdom would claim necessary for 6.25kC bandwidth. If you use a good > > tight receiver with a reasonably quiet front end, there should be NO > > appreciable difference in range; the NB system could even be a bit > > better. > > Tom > > > > --- In Repeater-Builder@yahoogroups.com, DCFluX <dcflux@> wrote: > >> > >> As receiver bandwidth narrows, higher frequency stability is required. > >> Handhelds with ovenized reference oscillators are not very practical. > >> > >> On Fri, Aug 27, 2010 at 8:01 PM, Matthew Kaufman <matthew@> wrote: > >> > On 8/27/2010 7:33 PM, larynl2 wrote: > >> >> This has always interested me, and I've never seen a good technical > >> >> reason for a loss of range with narrow deviation and receivers, > >> >> either. But<somewhere> one must exist. If it didn't, there'd be no > >> >> reason not to take analog deviation down to say, 1 kc., or 0.1 kc., > >> >> would there? > >> > > >> > There are several good references online. A good balance between > >> > theory > >> > and understandability is at: > >> > > >> > http://urgentcomm.com/networks_and_systems/mag/narrowbanding-system-coverage-effect-201004/ > >> > > >> > and > >> > > >> > http://www.adcommeng.com/Narrowbanding_for_Technicians.pdf > >> > > >> > Essentially as the modulation index goes down, the difference between > >> > the modulated signal and noise becomes lower, and so more signal > >> > strength (to better saturate the FM receiver's detector) is required > >> > to > >> > compensate. > >> > > >> >> And I don't think that knowing a repeater's tail signal strength > >> >> doesn't change is an apples to apples comparison. > >> > It is all about intelligibility of the modulated signal, not the > >> > quieting of the unmodulated signal. In fact, for the unmodulated case > >> > the narrower IF filters make narrowband *better*. > >> > > >> > Matthew Kaufman > >> > > >> > > >> > > >> > ------------------------------------ > >> > > >> > > >> > > >> > Yahoo! Groups Links > >> > > >> > > >> > > >> > > >> > > > > > > > > > > ------------------------------------ > > > > > > > > Yahoo! Groups Links > > > > > > > > > ------------------------------------ Yahoo! Groups Links -------------------------------------------------------------------------------- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 9.0.851 / Virus Database: 271.1.1/3098 - Release Date: 08/27/10 14:34:00
