[App_rpt-users] App_rpt-users Digest, Vol 88, Issue 16

[David McGough]

Hi Joe,

I'm not sure how you would pull off phase-coherence between nodes, even if
you could phase-lock all the 9.6MHz clocks....You have to remember that
the software on each node would have to be in perfect sync between each
node as well.

I think the bigger issue in overlap areas, with moving users, will be 
Doppler shift between the transmitter sites. With analog systems, Doppler 
shift is going to be a hard issue to resolve.

73, David KB4FXC



On Mon, 6 Jun 2016, Joe Leikhim wrote:

> There was mention on this board that drift of the 9.6 MHz clock causes 
> the CTCSS phase to shift. If this is the case, you will have audible 
> noise and possibly receiver CTCSS drop outs in overlap areas. You will 
> have distortion of audio frequencies as well.
> 
> Whatever solution to the 9.6 MHz clock must be phase coherent between 
> RTCM nodes .
> 
> I have no experience with RTCM, but am quite familiar with commercial 
> simulcast in the LMR world. I am lurking here because I see the RTCM as 
> a very affordable contender to the commercial products that exist today.
> 
> Joe K4SAT
> 
> 
> On 6/6/2016 12:23 PM, Jeff Carrier wrote:
> > The RTCM and simulcast DOES work.  As mentioned before, you have to be 
> > using a transmitter that can accept a 10 mHz (or whatever) reference 
> > signal.  You also need 1 PPS for your receivers and transmitter.  You 
> > also need to sync the RTCM to your GPSDO (which I have not done).  If 
> > you have not done all this you WILL hear some "funk" in the overlap 
> > areas.
> >
> > That "funk" can go from usable to un-usable depending on how strong 
> > the transmitters are in the overlap region.
> >
> > Pardon the "non-technical" terms.  It does work but the law of physics 
> > do apply here.
> >
> > de K0JSC
> >