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

[Sam Skolfield]

David, all the simulcasting RTCMs are driven by one node.

On Monday, June 6, 2016, David McGough <kb4fxc at inttek.net> wrote:

>
> 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
> > >
>
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-- 
KJ6QFS
Sam Skolfield
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