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voting comparator repeater

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#1 zap

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Posted 18 September 2014 - 04:48 PM

Anyone ever though of implementing a voting system on GMRS? Just curious.



#2 WQEJ577

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Posted 18 September 2014 - 10:00 PM

I haven't scoured the rules again to see what would prevent this, but the major issue is how do you get your RX audio to your main TX site? Given my knowledge of the rules, you cannot use RF (whether in or out of the service) and you can't use a phone line. That leaves running your own hard wire (not a phone line, and not practical) or using the Internet.

 

Allstar has an "RTCM" which is a thin client computer that interfaces with your RX or repeater and the Internet to send/receive audio to an Asterisk server at the TX site. You can use a receiver and an RTCM at each voter receiver site and another at the transmitter site. With the proper oscillator and transmitter, you can even run a simulcast system. A GPS is also used to keep the voter receiver audio streams synchronized in order to avoid issues with network latency. After all, there's no sense in comparing the SNR if your streams are all coming in differently!

 

Not sure how any of that fits in with GMRS offhand, though. It's an interesting idea, though.


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#3 quarterwave

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Posted 19 September 2014 - 09:49 PM

Just to chime in on... "A GPS is also used to keep the voter receiver audio streams synchronized in order to avoid issues with network latency"...GPS is used for TX on the simulcast, it is not used on the receivers, as only the best audio is voted. 

 

I am very familiar with a couple of these systems. One in my area that is UHF uses 5 sites, 4 outlying, 1 central (hub). Each outlying site is a MTR2000 repeater which has it's TX and RX "separated".  The same is true for the central site, there is just more equipment there. Each receiver listens on the same input freq and pl. Audio is sent to the hub site via leased lines where it goes into the voter, along with the RX audio from the central site, which is local to the voter, of course. The voter decides which of up to 5 audio signals is best, and locks in that one (I can't remember how often it re-samples, but it does). 

 

From there, TX audio is sent to the central repeater TX and the 4 outlying repeaters via an RF link that is about 10 watts, has yagi's pointing 4 directions. Audio is received at the sites, synced to GPS, delayed if necessary, and the transmitted from all 5 sites at once. The result is massive coverage. The voting can be bypassed with a channel that is programmed in the mobiles/portables which carries a different input PL, and is locally hardwired to trigger just the central local TX if activated. It's a phase 1 fail-safe so to speak. The central site also has a backup repeater and antenna which is kept disconnected from power and Tline, and only plugged in if needed. This is to keep it safe from lightning damage, etc. It has yet a third input PL. This agency also has a secondary single site repeater on standby at another site, on a totally different freq. The voting system is 453 with 465 for link outs. It has worked well for 16+ years. I wish the users knew more about their equipment, and they would keep up monthly maintenance to balance line levels, etc...but like most public agencies, money can be an issue.

 

So I have seen the links done both ways, wireline or RF, or a combination as above.

 

I am the admin for my companies system. I used to work in radio, so I get to be the guy. I took our voting system back to single site. We had a main site where the TX/RX was, and then 2 other RX only sites, which came back to the voter on wireline. The voter was mainly added for some data terminal project they tried to do in the early 2000's and gave up on, which also made everyone stop using the radios because there was now data on the channel all day, so people turned them down and forgot about them. The company also bought everyone a cell phone. Since they only added the additional RX sites to get better data signals (which is harder than analog voice) over the voice channel, and we were having issues keeping the lines balanced and voter working, I had it removed. Now that I have a stand alone MTR2000 again, the system works great, all the stray, forgotten about radios with data boxes that went on aimlessly squaking day in, day out for years while no one paid attention are gone. When I took it on in 2012 it was to reorganize it, re-license and narrow band.

 

Now, about half the fleet has radios again, more will get them when new trucks come in to replace older ones. They still have cell phones, of course, but now they have radios that will make use of the repeater, and simplex for back up, in case they need it, or just for quick coordination in the field. We have 2 bases with 6-7 remotes too. The system is VHF on an exclusive channel, with a wide split, licensed for 350 watts, 500 Erp. We owned the tower until this year, and it is a nice high profile mountain top site. The RX antenna is at 270 feet, and the TX is at 180. I run it at 100 watts with no duplexer. 6+ MHz split. We used to have a filter on the TX site, but it was stealing 30% of the power, so I took it off. My M shop checked it all out...no de-sense.  

 

We have a 75 Mile license, but this thing can be heard 150 miles. There is no way we would get the same license with the same specs applying today, so I told them never to let it go. We use talkaround and 2 Itinerants as well, and I put 5 weather channels in the CDM mobiles. 

 

Sorry for the long story telling, but I wanted to share some insight, and I know I like reading about whats out there. I know these are not GMRS, but the examples lend themselves to the original questions.



#4 simpleskye

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Posted 20 September 2014 - 09:28 PM

Like WQEJ577 was saying, the rules disallow transmitting "...messages which are both conveyed by a wireline control link and transmitted by a GMRS station".

 

Plus, even if we could find a loop hole using microwave or something, the cost of the equipment is kinda ridiculous.



#5 quarterwave

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Posted 20 September 2014 - 10:20 PM

Like WQEJ577 was saying, the rules disallow transmitting "...messages which are both conveyed by a wireline control link and transmitted by a GMRS station".

 

Plus, even if we could find a loop hole using microwave or something, the cost of the equipment is kinda ridiculous.

 

 

Yes, it is kind of a self solving issue, since most individual GMRS operators are not going to go to the lengths, especially financially, to set up this elaborate of a system. 

 

However, there is some unclear definition to the ancient rules concerning "wireline control link". In the subpart that says you cannot connect to the PTSN (dial up phone system) it does say the exception is wireline control, and mentions part 95.127 which is not listed with the other sules on the FCC site at all. I did find it in a separate PDF, but part of one of the paragraphs in truncated in the FCC's own document, so who knows... 

 

I remember this terminology used in commercial part 90 years ago, and what it was written to mean was you could not use your radio, whereas you had the use of a telephone, wireline intercom, order wire, etc, readily available to give the same message over, and you should not do both. I am guessing this had something to do with air time, or controlling unnecessary transmissions for preservation of spectrum availability.

 

All in all, it boils down to theory, as who would really go to the trouble.

 

In the end, what might make more sense for the adventuresome operator, is what a few county organizations I have seen do when they didn't have funding for voting or elaborate systems, and that is to simply install multiple single site repeaters with different input tones, but the same output tone, all on the same freq. Then, you just steer it by switching the programmed channels in your radio according to which site you can hit, and since you can normally hear more that you can hit, you could communicate with someone when each of you were using a different site.    



#6 JohnE

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Posted 22 September 2014 - 07:53 AM

However, there is some unclear definition to the ancient rules concerning "wireline control link". In the subpart that says you cannot connect to the PTSN (dial up phone system)

 

 

that means in simple terms no phone patch

the other refers to remote control of the radio over leased lines other wise known as a radio tie line.

tie lines are used in a voting system but as stated previously it would be cost prohibitive for the average person just putting up a repeater.    


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#7 quarterwave

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Posted 22 September 2014 - 08:28 AM

I agree. Although, they do seperately mention "interconnection" which is specifically phone patch. 

 

I think for GMRS, poor mans trunking would be the way to go for someone who wants to play. Multiple repeaters, different locations on same freqs with different input PL's. I have seen this done with radios that scan and use last channel talkback...so it, for the most, part channel steered for you. But even doing it manually, could be ok. The system I have in mind that a fire department uses, they just announce what "tower" they are on.  



#8 WQEJ577

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Posted 22 September 2014 - 11:18 AM

Quarterwave, in the particular system I'm referring to, GPS is also used on the receiver sites, not just for the simulcast transmitter. The reason is that since the transport mechanism is the Internet, and not RF or hardline links, packets will be arriving at different times due to the network routing over the Internet. If you were to compare the receiver audio of all streams in realtime, it's virtually guaranteed that none of the streams would be in-phase, thus comparing SNR is moot. By timestamping each audio stream with GPS time, then having a GPS at the TX site, you can buffer all the receivers in such a way that they are in-phase and your SNR calculation would be accurate. You're right though, because when you're using RF or, say, a leased phone line, you don't have such a drastic delay in the audio from the receivers, so you can vote much easier. 

 

This is the device I was referring to, which is used on the Allstar link on Ham. You can repurpose it for GMRS as long as you don't connect to a Ham network in any way (such as the system I'm running: https://forums.mygmr...ing-discussion/).

 

http://www.micro-node.com/thin-m1.html


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#9 quarterwave

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Posted 23 September 2014 - 09:30 AM

Gotcha. Yes, if you were using the internet for back haul, you would certainly need something to re-time it all. Fiber or T1 would be ok, but not internet. 



#10 zap

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Posted 23 September 2014 - 09:54 AM

Gotcha. Yes, if you were using the internet for back haul, you would certainly need something to re-time it all. Fiber or T1 would be ok, but not internet.

What about your own sub-net for all of your links?

Legalities aside, one could use simplex channels for the control links, however, at that point it is far easier just to setup separate repeaters with a link radio for all three outlying repeaters.

#11 JohnE

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Posted 23 September 2014 - 04:45 PM

lot of things can be done

time and $$$$


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#12 quarterwave

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Posted 24 September 2014 - 08:35 AM

I've spent a lot of money while daydreaming.... :)



#13 JohnE

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Posted 24 September 2014 - 05:30 PM

:D  I can totally relate.


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