Batboard

Hello all,
I wonder if some of you guys are familiar with off the shelf equipment to automatically switch between a primary and backup base radio or repeater or control station? I have a need for this configuration for our 911 dispatch. According to NFPA and ISO guidelines I need to implement this with control stations and repeaters. I would have to determine which faults would trigger an automatic switchover and how to do it manually via the dispatch console. The dispatch console is a Zetron 4024 with 4 positions, also have an Aux/IO card installed on the Zetron.
I hope someone will have run into this before and give me an idea of ways to implement this. Budget is not too limited for this so if you know of off the shelf units that may do the switching and notify techs via pager or phone that info would be very helpful.
Thank you,
ecsradio.

[quote="ecsradio"]Hello all,
I wonder if some of you guys are familiar with off the shelf equipment to automatically switch between a primary and backup base radio or repeater or control station? I have a need for this configuration for our 911 dispatch. According to NFPA and ISO guidelines I need to implement this with control stations and repeaters. I would have to determine which faults would trigger an automatic switchover and how to do it manually via the dispatch console. The dispatch console is a Zetron 4024 with 4 positions, also have an Aux/IO card installed on the Zetron.
I hope someone will have run into this before and give me an idea of ways to implement this. Budget is not too limited for this so if you know of off the shelf units that may do the switching and notify techs via pager or phone that info would be very helpful.
Thank you,
ecsradio.[/quote]


Unless I have missed something along the way and over the years, I think you might have a slight miss on what your reading in NFPA and the ISO guidlines. I think it states you should have a backup radio. Not that it requires an auto change over.

I have been working in public safety communications systems for about 35 years now and travel all over the county to many 911 dispatch centers. Your the first one that has ever asked for an auto change over.

What many of the department do is to have a second repeater and use it in a couple of ways. Some of them send out a DTMF series of tones to activate the second or backup repeater. Others just put a different tone squelch code on the receiver and select which repeater they want by changing tone squelches.

Just to make sure I am not missing something, could you give the chapter and verse where it states you must have an auto change over. I would like to read that myself. Want to make sure that I am not telling the wrong way of doing things when I visit a dispatch 911 center and get paid for radio consulting.

Jim

If you are using conventional Quantars, you can achieve automatic Main/Standby switching without any additional hardware. The wiring (between certain pins on the Telco connectors of the two Quantars) and required wildcard programming are described in the back of the Quantar "Instruction Manual" (68P81095E04-B).

A summary of the function from that source:

Automatic Switchover: Whenever one of the modules fails in the Main station, the Main station will automatically set itself to Standby and will signal its companion station to set itself to Main. The Main station will not switch to Standby unless it is connected to is companion station and the companion station has not indicated a failure mode.

Tone Remote Controlled Switchover: Sending a function tone 4 to the stations will force the Main station to Standby mode and the Standby station to Main mode. Sending function tone 5 to the stations will force the Main station back to Main and the Standby station back to Standby mode. If either station has detected a module failure, neither switchover will occur.

External Control Switchover: An external control device may be connection to Input 2 on Connector #17 to initate a Main-to-Standby or a Standby-to-Main switchover to occur. Grounding this signal cauess the Main Station to go to Standby mode and the Standby station to go to Main mode.

The programming also includes functioning of an antenna relay (if the two stations are co-located and sharing an antenna) and a status request function.

If you're looking into Main/Standby switching, you should also take a look at FBICR programming (which is entirely internal to the station). This deals with the distinct issue of failure of the voting selector (versus a failure of the base station). In essence, FBICR tells the station to swtich from base station mode (dependent on the voting selector for xmit audio and PTT function) to repeater mode (keying itself on valid rx via its own receiver and repeating that receiver's audio) whenever its own receiver detects valid freq and tone but not associated voter PTT signal within a defined period of time. The FBICR function will only operate on a station set as "Main", so whichever of your two stations is presently the main will implement FBICR, if needed.

Hello Jim,
Thank you for your input. I appreciate hearing from you about this since you are a consultant. I admit I am not sharp on the subject of NFPA and/or ISO guidelines, it is kind of like reading a Microsoft license agreement
I have customers coming at me saying this is what it says and this is what the ISO man says and frankly I could use a bit of clarification on the system configuration they are trying to achieve to make their particular ISO guy happy.
I am going to try to talk directly with this guy tomorrow. I have on this system, a GE Mastr III with a voter and 4 receivers. I would like to have a backup repeater for this county wide volunteer fire alerting system. I thought of doing what RKG said about the Quantar system with the GE by using DTMF and enabling TX DISABLE on one system and disabling TX disable on another system, dispensing with the voting receivers while on backup.
Is it necessary on the NFPA to have a separate antenna and feedline to the backup?


I had talked to the ISO guy a year and a half ago and he was wanting to see an automatic switchover of repeaters to give them the rating they were seeking. However, it kind of got put on the backburner til now when a new dispatch center is under construction. Maybe he wasn't familiar enough with the guidelines? When I saw what he was asking for and read some of the NFPA I got more confused and wanted to talk to someone who had seen a system in place that did meet the guidelines.
I believe the system can be more simple and I think you can help with your experience.
The system is VHF conventional with 2 tone alerting for volunteer fire departments

I appreciate you and RKG replying to my post.
RKG - I do not have the Quantar but it really does sound like a very versatile system and able to do some very interesting things. I wish I had one in place of this GE stuff anyday!
Thanks,
Brian
ecsradio

I've installed auto-switching main/standby Quantars as RKG describes and is very slick and 'off the shelf'.

You make a good, and critical, point about alarming the switch-- how else would you know that it swithced itself? Since you are familiar with Zetron, they do make some very reliable dial out/ page out alarm panels- I've used several of the Sentri-dial panels and they worked great.

Quantars with the wildcard have good alarm output options. Other models\ makes may or may not. In that case, external RF power sensors are handy, especially for continuous duty stations. Otherwise, the RF power sensor output only matters during a PTT, and the design needs to account for that.

Automatic switching also depend on what equipment you currently have. Again, Quantars make it easy. Otherwise, things like the RF power fail, dc power fail, etc can also be used to activate a transfer switch. A transfer switch could be as simple as a control line relay and an antenna relay. When Eagle was still making paging transmitters, they had a fancy auto-transfer rack mount panel for this purpose. It's been a while since I looked around for similar products so I'm not sure whats available today.

Good Luck!
SZ

You got me thinking on this one and I pulled the books out. What I found is probably where the confusion has come in by someone not reading carefully enough. Let me see if I can explain this without causing a great turmoil and getting a bunch of hate mail.

In NFPA 1221 "Standard for the Installation, Maintenance and Use of Emergency Services Communications Systems" in chapeter 8 section 8.1.1.4 it states:

The primary dispatch circuit shall be provided with one of, or a combination of, the following:

(1) Wired circuit monitored for integrity.

(2) Analog voice radio channel with duplicate base transmitters, tranceivers, repeaters, receivers (where required), microphones, encoders control circuitry and antennas capable of visual and audible alerting of failure of signal activation as required by 8.1.2.6.

(3) Microwave carrier channel monitored for integrity.

(4) Polling or self-interrograting digital data radio channel with the following features:

(a) Automatic switchover to the second transmitter if the primary transmitter fails upon operation.

(b) Audible and visual indications to the telecommunicator.

(5) Approved, dedicated telephone circuit that is monitored for integrity, excluding the following:

(a) Telephone Connection through a public-switched telephone network via regular dial-up mode.

(b) Nondedicated phone lines.

(6) Where used as the primary dispatch circuit, trunked radio systems in compliance with 8.1.1.4(2) or 8.1.1.4(4)

8.2.1.6 A Separate tie circuit shall be provided from the communications center to each subsidiary communications center.


Bottom line is that who ever told you that you need to have an automaitc switchover of your radio system has miss read the fine print. The interpitation to 8.1.1.4(4)(a) is talking about a digital data radio channel. This is normally called a SCADA system (supervisory control / data acquistion). These are normally used to monitor the status of things like wells, pumps, remote fire alarms, and the many control functions it can do. Many public safety agencies use these SCADA systems to do fire station alerting.

If you go back and re read the 8.1.1.4(2), it just says an analog voice radio channel with (DUPLICATE) base transmitters, transceivers, repeaters, etc. This means that all you need is a secondary radio system to do the dispatching over. It doesn't call for an automatic chage from primary radio to the backup.

The other point that I would like to make and again please don't everyone get riled by it. The NFPA standards are just guide lines. There is no mandate to force them down the throats of any agency. Most of what is in the standards is well stated and came about over many years of practicle use.

As for the ISO inspectors, they are a bread all to them selfs. I have tangled with a couple of them that think they are god. All I do is try to be polite and ask them to produce the written document that enforces what they are trying to tell you is wrong or has to be changed. You may cause a stir if you get the "Because I said so." line from them. Stay cool and make a phone call to the office and try to find someone else that you can talk to about the issue. Most of the time if your following the NFPA guide lines, your on firm ground.

Another point is that ISO is making changes all the time and they don't follow the NFPA standard guide lines all the time. I have seen a few cases where the ISO was ahead of the NFPA in making updates and changes. Just try and get them to work with you.

Hope this helps in trying to figure out where your going and why.

Jim

I make no claim to great expertise with Mastr IIIs, but if you get out the Mastr III programming book (TQ-3353-V12), it appears that you can define TRC tones to set and disable a repeater disable function. (Start at page 4-106 and read on a bit; the book isn't as clear as it could be.) If that is so, you could set TRC T14 to be RptDis clear in the Main machine and RptDis set in the standby machine, and vice versa for TRC T15. Sending T14 down the line to both machines would make the Main machine active and sending T15 down the line would make the Standby machine active.

I want to thank you all for your replies and just taking the time to respond. I think I have enough information to go on now. I will look into the MastrIII manual and see about setting up the system like RKG suggests.
As for you Jim, Thank you for your qualified input. I will go back and re-read section 8.1.2.6 and have a better understanding before I tackle this ISO guy.
I can install duplicate control stations and repeaters, it was just the idea of automatically switching and monitoring for integrity that was hanging me up.
Again many thanks!
Brian
ecsradio.

Hi,

I'd be really shy of putting in automatic switch over. The transfer logic, relays, and dual repeaters/transmitters adds in a new failure point that you didn't have before. The Keep it Simple principle applies here too.

In our PSAP we run a Zetron 4048 for our paging into wide area voted simulcast for most fire districts in our county and a repeater to fill in two pockets where simulcast doesn't have the density to do paging.

We don't postulate a "double" failure when we consider backup; only single failure is considered. So, if Zetron was down, repeaters and simulcast would still be up. If simulcast was down, repeaters and Zetron would still be up. If repeaters were down, Zetron and simulcast would be up.

So, the only thing we need to duplicate is the tone generation and control station capability. We use a Motorola MCS in Zones at each work primary work station. A Zetron Model 15P has retrofitted onto it a mic connector for the MCS. Thus, the mobile can be used to generate paging and replace the control station, base station, or the console.

Good luck with your project, Bob