[App_rpt-users] Digital audio

Steve Wright info at meshnetworks.co.nz
Wed Mar 30 20:47:23 EDT 2016


On 31/03/16 13:26, Joe Leikhim <rhyolite at leikhim.com> wrote:
> A lot of early simulcast systems "didn't work" because the designers
> ignored problems of time differential interference in overlap areas. Or
> ignored problems of transmitter stability, audio level equalization.
> Small things like having the audio phase 180 degrees out of phase (doh,
> signal wires transposed!), CTCSS tone out of phase. A lot can go wrong
> and the product still be solid. That is what I am wondering.

I understand RTCM TX Simulcast addresses all those concerns, but they 
were unhappy enough with the result to announce it "non working", which 
is a great loss to me.  I've not heard or seen a demonstration of this - 
maybe someone has a video of it, or might offer an anecdote.


> By the way if you have a high site, lots of ERP, no reason not to use
> voter for multiple antenna diversity co located on the site. No back
> haul needed.

Those places are getting expensive here.  I like the voter idea, because 
we can reuse inexpensive sites - and just add more of them. Receivers 
and Ubiq radios are cheap as chips, and you can just throw one into any 
gap, with a big antenna and a quality preamp on it. That'll work. ;)


> I am with you on digital audio CODECs. I am not sold. But there is
> something to be said for 15 sites of DMR 2-slot TDMA linked with
> internet and mobiles free to roam automatically.

We could do better in my opinion.  The interesting thing about any Voter 
system, is that the receivers do not have to be sited with their 
transmitter.  So lots of problems go out the window.  No duplexing and 
no power limitations are the big ones...  Imagine what you can do on a 
6/2/70 repeater site when there is no duplexing and no power 
limitations!  1500 watt analog repeater, anyone?

Single-site digital systems have similar advantages, again no duplexing 
and no power limits.  Cue 100watt 1.3GHz 10mbit for Hams? Multi-site 
zero-handoff all done in software?

Really great tech chat, Joe. :)


Steve







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