[App_rpt-users] App_rpt-users Digest, Vol 85, Issue 58

Joe Leikhim rhyolite at leikhim.com
Wed Mar 30 20:15:07 EDT 2016

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.

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.

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.

On 3/30/2016 7:54 PM, Steve Wright wrote:
> On 31/03/16 11:46, Joe Leikhim <rhyolite at leikhim.com>wrote:
>> What is the problem with the RTCM and simulcast?
> RTCM Transmit simulcast "doesn't work", we were told.  I haven't tried 
> it.
> RTCM Receive voting works famously.
>> Analog simulcast may never sound as good as a single site, because it
>> does experience/cause time differential interference and noise and
>> therefore requires some very specific design constraints. However, for
>> some applications it still is the way to go.
> How difficult for Hams?  RTCM TX Simulcast is a very good idea, but it 
> seems to be on the back burner.
>> Moving forward 5-10 years,
>> two slot DMR with IP connectivity will be the way to go. Before I get
>> flamed, TETRA never got a foothold in the US and because FCC eliminated
>> most 25KHz channels, getting TETRA to play in the US is reserved for
>> those few who have the contiguous spectrum.
> We're Hams though, and we can do as we choose within our own 
> regulations, and our propensity to negotiate new rules.  I don't like 
> 4800baud audio, and if we don't want to do something, then we don't 
> have to do that.  There's no need to focus on the commercial world and 
> their limitations and rules, but we just don't have to.
>> [....] commercial products are very pricey and complex. That
>> being said, I see the RTCM as having some potential niche in the
>> commercial LMR world.
> All the commercial stuff WILL go digital.  That's my prediction 
> anyway.  There's too much cleverness in the digital RF world to be 
> ignored now - the benefits are just too great and the products are too 
> disruptive.  There won't be any analog RF before long - it'll be too 
> slow, too featureless, too expensive, too power-hungry, and almost 
> anything else you can think off.
> Maybe Hams are stuck with that reality - that an analog RF high-site 
> will be cool and quaint, like a transistor analog VFO. Nice and 
> old-world to play with, but not enough toys in the toybox.
> For myself, I just can't get past the horrible 4800baud audio, and I 
> don't think that we have to - not on VHF/SHF anyway.  A nice 64kbit 
> channel would be lovely thanks! :p
> Steve
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Joe Leikhim

Leikhim and Associates

Communications Consultants

Oviedo, Florida

JLeikhim at Leikhim.com



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