Re: [App_rpt-users] App_rpt-users Digest, Vol 85, Issue 58
On 31/03/16 11:46, Joe Leikhim <rhyolite@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
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@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@Leikhim.com 407-982-0446 WWW.LEIKHIM.COM
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.
This is a great/simple/effective idea. Don't know why we didn't think about this sooner. And I work in an industry that thrives on diversity reception. It will greatly help the swishing handhelds. The 2m repeater actually has remote receivers but need to implement a 2 chan voter for 440. And the 900. tnx Mike / W5JR Alpharetta GA
I have a project on my bench to put together a UHF 4-receiver diversity repeater based on a JPS DSP voter. In planning this I read a lot of work by C. Y Lee about diversity. With two branches you need the antennas separated vertically on the tower which means lower elevation for one, but still better than just one branch. If you want all on same level, like a rooftop or tower with cross arms, he recommended three branches or more to avoid having two antennas correlated (less effective) in two directions. I am going with four antennas and the fourth will be horizontally polarized. All I need is more time and money. I have one not both at the moment. What I am hoping to do is get it built and run some drive testing to compare talk back with 1, 2, 3 and 4 antennas. My idea is that with the cost of deploying commercial sites, it may be more attractive to enhance a single site cell. On 3/30/2016 8:51 PM, Mike - W5JR wrote:
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.
This is a great/simple/effective idea. Don't know why we didn't think about this sooner. And I work in an industry that thrives on diversity reception. It will greatly help the swishing handhelds. The 2m repeater actually has remote receivers but need to implement a 2 chan voter for 440. And the 900.
tnx Mike / W5JR Alpharetta GA
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To unsubscribe from this list please visit http://ohnosec.org/cgi-bin/mailman/listinfo/app_rpt-users and scroll down to the bottom of the page. Enter your email address and press the "Unsubscribe or edit options button" You do not need a password to unsubscribe, you can do it via email confirmation. If you have trouble unsubscribing, please send a message to the list detailing the problem.
-- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida JLeikhim@Leikhim.com 407-982-0446 WWW.LEIKHIM.COM
participants (3)
-
Joe Leikhim -
Mike - W5JR -
Steve Wright