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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