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some simulcast questions
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Hey guys,
OK, so here we go. I've been given a challenge, to help an fd get better coverage. We've gotta take this 1 step at a time. So right now they are on vhf. They have a single site repeater. We're thinking simulcast right now. The repeater is a quantar. So, keeping the current repeater in its current home, let's ay we add 1 more to the mix, doing a simulcast, what would we need? This is my 1st simulcast adventure, and i actually wanna learn more about it to help them out. Thanks, Jed |
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To start with:
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For transmit, both sites would need a high stability oscillator, possibly GPS disciplined. Identical equipment at both sites would make things easier. For receive, both transmit sites need to broadcast the same audio at a specific time. If you are going to receive at both sites you would need a way to vote or chose which site audio to use at a particular point in time. You would need a link between both sites, preferably an RF link. Internet linking can be done but makes timing extremely difficult and expensive. This link would carry the receive audio between the sites. I assume that these are going to be conventional FM analog repeaters. Overlap areas need to be planned and managed by audio delays. There will be areas that will have audio that is far from perfect. Joe On 9/9/2018 6:25 PM, Jed Barton jed@... [Repeater-Builder] wrote:
Hey guys, |
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The easiest approach might be for the far repeater to receive the near repeater then retransmit the message.
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Set the retransmit delay on each repeater different so that they will not all be transmitting at the same time. To get true simulcast the repeater transmit oscillators have to be phase synchronized IIRC. if the problem is that the field units cannot get back to the repeater, but, can hear it, you might want to try satellite receivers. I have never done this so this is just theory. 73 Glenn WB4UIV On 9/9/2018 6:25 PM, Jed Barton jed@... [Repeater-Builder] wrote:
Hey guys, --
----------------------------------------------------------------------- Glenn Little ARRL Technical Specialist QCWA LM 28417 Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178 QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR "It is not the class of license that the Amateur holds but the class of the Amateur that holds the license" |
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exactly. So, my gut is telling me, make the quantar go away. It's
rather old and they don't even make them any more. For voters, i was thinking the jps voters. As for a repeater, not sure what to go with. Any ideas? On 9/9/18, Joe k1ike_mail@... [Repeater-Builder] <Repeater-Builder@...> wrote: To start with: |
¿ªÔÆÌåÓýIs it an issue where the repeater is not able to hear the remote users? If so use a voting system. All receivers should be the same make and model so that their audio characteristics are the same.?RF link preferred but You can use a non public IP network if desired. It will cost you more monthly but you can get QOS to not drop any audio packets. You will also have to have good vocoders as well.? Stan? On Sep 9, 2018, at 5:25 PM, Jed Barton jed@... [Repeater-Builder] <Repeater-Builder@...> wrote:
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If they are analog and transmit PL, and have overlapping coverage, you¡¯ll hear a buzz in those areas unless the PL on both signals is in-phase at the receiver. That¡¯s the extent of my simulcast experience.
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On Sep 9, 2018, at 3:25 PM, Jed Barton jed@... [Repeater-Builder] <Repeater-Builder@...> wrote: |
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Jed,
You should keep all the transmitters the same. In simulcast the main concerns will be in the overlap areas. The issues are more phase related than frequency offsets and audio deviation differences, although both of those are important as well. Most all simulcast systems are locked to a very stable time base to keep frequencies the same. The systems that I work with are GPS disciplined and the exciters are DSP based. In the overlap areas ( area where the user can hear both or many transmitters ) phase distortion can make the area unusable. This is why it is very important in a simulcast system to carefully design the RF coverage. More power and high gain antennas mounted high are not always the best solution for simulcast. Simulcast concerns are very different between analog and digital systems. On analog it helps to use the same service monitor to set the frequencies and deviations, but if you are using a high stability time base at the transmitters then this is not so important. I am trying to just give some pointers. I can move to a different email if you want more in depth explanations. The systems that I design, build and maintain consists of up to 250 high power transmitters located in the same state all simulcast. 73, Ken, N4KCD |
Hey guys,The first thing is to write a specifications sheet, meaning a signal strength overlaid map that shows the existing coverage area and the difference or changes made by adding one or more additional transmitters. All this determines the hardware options that drive the resultant as-built system. This is my 1st simulcast adventure, and i actually wannaYou would start with a logical game plan first. Simulcast Systems don't always have to be really complicated and they don't have to have all the same brand and model equipment. That's what the learning curve is about... Another big deal is the financial side of the equation... if you're a Public Safety system where money seems to be spent like drunken sailors in port, the path taken is a whole lot different compared to a couple of smart thinking private two-way radio people... also a reasonable Amateur (Ham) System. There are many types of Simulcast Systems... so a proper game plan at the start saves time, money and hair color or quantity there of. Just tossing out a "you need this or that" is probably not the optimal first path. Cheers, Clairol Natural Instincts s. |
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Many years past, some Schaumberg IL Motorola Engineers made a
field recording of a simulcast paging system in various states of alignment. The demonstrated audio included two transmitters in a well aligned simulcast system. One transmitter was then moved off frequency to a number of different places, the distortion became audible. The transmitters were reset to the same frequency, next the audio delay values were modified, no longer synchronized... a different type of distortion became audible. Audio frequency equalization and (group) delay is considered an important part of a simulcast system. These parameters were varied with the example system, a third and forth type of distortion became audible. Stability is another important consideration... an interesting helicopter blade beat note occurs when two transmitter frequencies are moving in relation to each other. In a modern Simulcast System, management of all the above requirements is mostly done in specialized (PC) software, over regular intervals. In older times, simulcast management required much more operator/owner think power/time. In each of the above described distortion examples, the resultant audio was totally different from any other source. Even worse when two or more parameters were not correct. With the advent of Ebay, GPS Technology and system upgrades, a lot of very useful hardware can be found. Over to Ebay, search CONVEX C20 AUDIO EQUALIZER and see what was once a whole lot of money being offered for $25 each, Having some of these cards around can be very useful in a budget minded simulcast system having decent quality commercial hardware in play. Then it's on you to make it work well.... based of course on reasonable expectations. cheers Dr House |
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Joe KC2IRV has done some great work with the Micronode RTCMs in a voted simulcasted setup. Take a look at his YouTube channel (KC2IRV)?
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KJ6QFS Sam Skolfield |
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I know we are talking about the technical aspects of this here. Since
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this is in the public service band and not amateur, you may run into some work with licenses. I haven't been there, but just something to think about with this before you get too carried away. A bit of information that may help, is it the transmit or receive that is the weak part of the repeater? Guessing it seems to be the repeater hearing the field units. Mick - W7CAT ----- Original Message -----
From: "Jed Barton jed@... [Repeater-Builder]" To: Repeater-Builder@... Sent: Sunday, September 09, 2018 05:06:41 PM Subject: Re: [Repeater-Builder] some simulcast questions > exactly. So, my gut is telling me, make the quantar go away. It's > rather old and they don't even make them any more. For voters, i was > thinking the jps voters. As for a repeater, not sure what to go with. > Any ideas? > > On 9/9/18, Joe k1ike_mail@... [Repeater-Builder] > wrote: > > To start with: > > > > For transmit, both sites would need a high stability oscillator, > > possibly GPS disciplined. > > > > Identical equipment at both sites would make things easier. > > > > For receive, both transmit sites need to broadcast the same audio at a > > specific time. If you are going to receive at both sites you would need > > a way to vote or chose which site audio to use at a particular point in > > time. > > > > You would need a link between both sites, preferably an RF link. > > Internet linking can be done but makes timing extremely difficult and > > expensive. This link would carry the receive audio between the sites. > > > > I assume that these are going to be conventional FM analog repeaters. > > Overlap areas need to be planned and managed by audio delays. There > > will be areas that will have audio that is far from perfect. > > > > Joe > > > > > > On 9/9/2018 6:25 PM, Jed Barton jed@... [Repeater-Builder] wrote: > >> Hey guys, > >> > >> OK, so here we go. I've been given a challenge, to help an fd get > >> better coverage. We've gotta take this 1 step at a time. So right > >> now they are on vhf. > >> They have a single site repeater. We're thinking simulcast right now. > >> The repeater is a quantar. So, keeping the current repeater in its > >> current home, let's ay we add 1 more to the mix, doing a simulcast, > >> what would we need? > >> This is my 1st simulcast adventure, and i actually wanna learn more > >> about it to help them out. > >> > >> Thanks, > >> Jed > > > -- Untitled Document Be sure to check out all the latest at our web site <;! <; 
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Before you do anything else, define what "better coverage" means.
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Do the field units have trouble hearing the repeater output? Do the field units have trouble being heard by the repeater? Or do both situations apply? Are the field units having problems with mobile radios, portable radios, or both? The existing coverage needs to be mapped and should be compared to a predicted coverage map based on the current equipment (radio/feedline/antenna). You need to know the area that the system "should" cover. On-line coverage prediction systems exist and can give a rough idea of system coverage. Talk-out(TX to field) and Talk-in(field to RX) should be considered for both mobiles and portables, they are not the same. The existing equipment, both fixed end and in the field, needs to be checked to see if everything is meeting spec. Next determine the desired area of coverage and show that on a map along with the current coverage. Then start asking more questions: Is it necessary to have the system act as a single repeater over the entire coverage area or can it be split up into smaller regions? Is the current repeater location at the best available location to cover the area in question? Is there interference of any sort on the existing frequencies in use? If the problem is talk-out, can the system be licensed to use a different antenna or higher TX power output? If the problem is talk-in, consider multiple receiver sites with or without receiver voting. Since this is a public safety system, I would strongly suggest engaging the services of a professional. Designing something like this by the seat of your pants is just asking for trouble. On 9/9/2018 6:25 PM, Jed Barton jed@... [Repeater-Builder] wrote:
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You can build an analog simulcast system on a budget, but you may not be satisfied with the audio quality results.? Using the same brand equipment throughout the system (including RF links) is not mandatory, but it does simplify the process of making the audio sound acceptable.? (Notice the wording "acceptable")
In the budget system you definitely would need to a disciplined oscillator to keep each site on frequency.? But, you do not want both sites on exactly the same frequency.? If both sites are exactly on the same frequency you can experience deep phasing nulls where the two sites cancel each other out.?? Instead, you can offset the two sites by, for example, 20 Hz.? This will cause a 20Hz buzz on the signal, but the low frequency filter in the receivers that filter off Pl tone should minimize the buzz.? This technique was used on a public safety system and documented in a publication many years ago. (Can't remember the name of the publication right now.) Again, this is the cheap and dirty way of doing simulcast.? Audio quality WILL suffer, but it will give communications quality analog audio.? I did something similar on a large Quintron paging system years ago that did both voice and digital paging.? It worked surprisingly well and the tiny speaker on the voice pagers filtered out the offset buzz.? We used crystal ovens to keep the system on frequency.? Crystal ovens will keep the transmitters on frequency but not in phase like a GPS system can do. Joe |
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Hey Jed, http://www.micro-node.com/thin-m1.shtml https://m.ebay.com/itm/GPS-Receiver-GPSDO-10MHz-1PPS-GPS-Disciplined-Clock-SINE-WAVE-GPS-RECEIVER-/262981677836 Good luck! Best regards, Ross kc7rjk On Sep 9, 2018 3:25 PM, "Jed Barton jed@... [Repeater-Builder]" <Repeater-Builder@...> wrote:
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No Part 90 use, we looked into similar for not for profit rescue group.? Was kindly told no for using outside HAM interests.? -- David Thurman Australian Shepherd Rescue Midwest - President (309)863-5211 Extention 402 (309)216-6444 Fax info@... On Mon, Sep 10, 2018, 7:41 AM Ross Johnson kc7rjk@... [Repeater-Builder] <Repeater-Builder@...> wrote:
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Since you are doing this for a FD it needs to be done correctly. Done poorly you will have distortion and paging tones will be distorted and fail, the audio poor and CTCSS may even suffer. You need to have exactly same transmitters on both ends. A good place to research the proper equipment is www.simulcastsolutions.com where you can research proven solutions,
Ed OConner has decades of experience and his site has a lot of application notes and studies. You will need someone to perform a simulcast coverage map if the proposed system. A proper map will take into account the differential time delay between sites and will highlight areas of potential distortion. You might get away without this step on a two site system if the sites are close to each other, however there will be time delay interference distortion and you need to know where it occurs duruping the planning stage. Someone brought up the RTCM. It is an attractive low cost alternative, however it has a design bug with resided to the 9.6 MHz clock. Fixing this is not simple. The RTCM is really not suitable for public safety instaklations. You will need a voter for simulcast and the JPS SNV12 is the only product I would recommen at this time. Linking sites requires a digital circuit that is low jitter and has stable latency. The internet won't work in this case. |
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Where exactly is the one repeater, and where exactly are you having coverage issues (and are they in one or more places, and is it indoors or out that's having the trouble)? A Quantar is actually a perfectly reasonable repeater to use for conventional simulcast, so I wouldn't be tossing that out. Lots of solutions involving wireline, old-school microwave, and of course IP-based wireless or wired solutions abound. But the first thing is to figure out, on a map, what you're trying to do. I've got a lot of experience filling in coverage gaps with my own homebuilt simulcast system, so shoot over some details. Matthew Kaufman Hey guys, |
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Another thing to think about is to do what a few fire departments around here have done... add another site, use the same input frequency at all sites with a voter, but have different outputs. Yes, you'll need another frequency coordinated, but you were going to have to do most of that for simulcast anyway. Both San Mateo County and Monterey County, California are running setups like this. Matthew Kaufman Hey guys, |
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Are you saying you can't use the rtcm because of legality? I don't believe that to be the case at all. Maybe it's different in Australia vs the US but I don't believe so.? Ross kc7rjk On Sep 10, 2018 5:45 AM, "David E Thurman david.e.thurman@... [Repeater-Builder]" <Repeater-Builder@...> wrote:
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¿ªÔÆÌåÓýMulticast might be easier... we have a couple of four site multicast sites operating in our area... poor man¡¯s way is w/ same repeater input, different squelch codes, and different transmitter frequencies. One county ties the four repeaters together at the console... and ours uses RF links between the four sites, via a rock and mobile radio.?On Sep 10, 2018, at 4:28 PM, Matthew Kaufman matthew@... [Repeater-Builder] <Repeater-Builder@...> wrote:
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RFI-EMI-GUY
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