David, all the simulcasting RTCMs are driven by one node.
On Monday, June 6, 2016, David McGough <kb4fxc@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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Sam Skolfield