Station alering system problem

[dmitry103]

Here's one for the stereo gurus out there.


Our station has been having a problem with the sound quality when alert goes off. Static noise overrides the voice notification and it's very difficult to hear dispatch info.


Here's the setup: Minitor V plugged into the charger&amplifier, audio then goes to a second amplifier that has 8 output channels to supply speakers around the house and the bays. The second amplifier model POWERPLAY PRO-8 (below picture for reference). The speakers we have installed are standard Motorola HSN9326A. My understanding so far is that the audio being amplified beyond the capacity of the speakers...but I'm no expert.


Any ideas and help would be highly appreciated. If you know a stereo specialist, feel free to refer me to one.


Be safe. Dmitry K.

 

[firemedic10584]

Here's one for the stereo gurus out there.

Our station has been having a problem with the sound quality when alert goes off. Static noise overrides the voice notification and it's very difficult to hear dispatch info.


Here's the setup: Minitor V plugged into the charger&amplifier, audio then goes to a second amplifier that has 8 output channels to supply speakers around the house and the bays. The second amplifier model POWERPLAY PRO-8 (below picture for reference). The speakers we have installed are standard Motorola HSN9326A. My understanding so far is that the audio being amplified beyond the capacity of the speakers...but I'm no expert.


Any ideas and help would be highly appreciated. If you know a stereo specialist, feel free to refer me to one.


Be safe. Dmitry K.

Our station does that as well....While I really know nothing about the amps...I have found that with multiple guys wearing individual pagers while inside the station, it some how interferes with the overhead pager...like you said, tones will alert, but the static is louder than the dispatcher and you can't understand what they're saying. I've noticed that if less individual pagers are in the station, the overhead alerts normally...but the more pagers, the more static...Just an observation I have noticed...maybe someone will know an actual solution.

 

[Steve0625]

Do you know if they are pulling amplified audio or flat audio from the charger-amp? If it is amplified audio, try turning the volume down on the charger amp and up on the PowerPlay. If the audio coming from the charger amp is already distorted, the PowerPlay just amplifies it and sends it on.


Second thought is to get an attenuated patch cord to connect the charger amp to the PowerPlay.


Has the Minitor V been narrowbanded? (I'm presuming your dispatch transmitter has been.) Did the static get better or worse after narrowbanding either the Minitor or the transmitter, or both? An easy thing to try is to reprogram the pager back to wideband. I am getting reports that some systems are encountering all kinds of distortion and strange sound from narrowbanded Minitor V's. The county next to us had that problem and they've gone back to wideband on the pagers with marked improvement in sound quality. (Before anyone panics, the FCC Narrowband mandate applies specifically to transmitter emissions. There are no requirements regarding receiver-only devices like our pagers.)


Also, depending on how many speakers you have on the system, you may be better off without the amp in the middle and just let the charger amp drive the whole thing, especially since you are using /\/\ standard speakers. If there are only a couple of speakers, this is doable, just run the speakers in parallel.

 

[dmitry103]

Do you know if they are pulling amplified audio or flat audio from the charger-amp?

Amplified from what I've been told.

If it is amplified audio, try turning the volume down on the charger amp and up on the PowerPlay. If the audio coming from the charger amp is already distorted, the PowerPlay just amplifies it and sends it on.

Ok, will try.

Second thought is to get an attenuated patch cord to connect the charger amp to the PowerPlay.

Has the Minitor V been narrowbanded? (I'm presuming your dispatch transmitter has been.) Did the static get better or worse after narrowbanding either the Minitor or the transmitter, or both? An easy thing to try is to reprogram the pager back to wideband. I am getting reports that some systems are encountering all kinds of distortion and strange sound from narrowbanded Minitor V's. The county next to us had that problem and they've gone back to wideband on the pagers with marked improvement in sound quality. (Before anyone panics, the FCC Narrowband mandate applies specifically to transmitter emissions. There are no requirements regarding receiver-only devices like our pagers.)

I will contact the county radio techs to find out info in regard to banding.

Also, depending on how many speakers you have on the system, you may be better off without the amp in the middle and just let the charger amp drive the whole thing, especially since you are using /\/\ standard speakers. If there are only a couple of speakers, this is doable, just run the speakers in parallel.

Total of 8 speakers. I had sent an email to Motorola techs asking for suggestion, so we'll see.

Thank you very much for your input. I will get back once we figure something out.

 

[kb4mdz]

"Static noise" would indicate to me that it is poor reception of the radio signal by the Minitor pager. If the radio signal into the pager is not what is termed 'full quieting' you will get a static-y noise. And once you have noise introduced into the audio amplification chain, you can't just 'take it out' or attenuate it with a patch cord. You have to improve the source.


Does the Minitor pager (& I assume the charging stand) have an EXTERNAL antenna on it? Either a wire whip of proper length for the frequency, or a real antenna either in the building or (preferably) outside?


A Minitor pager is NOT in my professional and not humble opinion, an acceptable way to alert a fire station and provide audio to speakers. It is by its very size a belt-worn paging reciever, with an antenna internal to the case, somehow folded in & around the circuit board. The amplified charging stand is a convenience.


I have personally tested Minitors, all versions, the old Minitors, the Minitor II & II, and IV & V, and can demonstrate what can best be described as 'body shadowing'; if you wear the pager on your belt, and place your body between the pager and and the direction of the transmitter when you are near the edge of the intended coverage area, reception is hindered.


Get a real radio, like a CDM1250 or a Kenwood, or something that has a real receiver, and a real live outside external antenna, and trip the lights & speakers that way. I can provide you with a great design that my municipal shop just put into 27 fire stations last year, and there are other designs around the web.


Sorry if I sound snarky & know it all; in converting said 27 fire stations my colleagues & I came across a large variety of ways of doing this function, from good function to barely passable and safety & fire hazards, all levels of audio quality. Some were very scary to rip out. All 27 stations now have the same basic design, and FF's at the stations are expressly forbidden from f*ck*ng with them.


But I'm glad to help y'all out.


I'll post some comments on the concept of 'full quieting' if anyone wants it, too.

 

[CPDG23]

Something I have noticed with my home set up....


I have a Bearcat BC355C scanner mounted up underneath the kitchen cabinets and powered from a 120vac receptacle, my department Motorola HT1250 portable radio charger is also in the kitchen on a different plug but same circuit.


If the HT1250 is on the charger base, I for some reason get horrible reception on the scanner and the 1250 if it's turned on, if I take the 1250 off the charger the issue goes away for both radios.


The common denominator is the charger base.


Try removing the pager from it's charger and see if the issue goes away. If it does you need to get the amplifier or pager (assuming it's on the same circuit) on a different circuits.


Not a radio expert by any stretch, just something I have an issue with at home.

 

[Steve0625]

"Static noise" would indicate to me that it is poor reception of the radio signal by the Minitor pager. If the radio signal into the pager is not what is termed 'full quieting' you will get a static-y noise. And once you have noise introduced into the audio amplification chain, you can't just 'take it out' or attenuate it with a patch cord. You have to improve the source.

My original reply was aimed mostly at improving the system on the amplifier side. You are absolutely right about the receiver improvement. Funny thing is that the CDM1250, if purchased used, is much cheaper than a Minitor V and charger amp. There are a lot of CDM's on the market now in fine condition due to agencies jumping to digital technologies.


I'd be interested in seeing your design for station alerting using the CDM. We have a system in our station now, but I am not 100% happy with it.


I think some of the folks here could really benefit from some more information about full quieting. I'd certainly like to hear your thoughts on the subject.

 

[kb4mdz]

Hmm, I've got it as a PDF; can I just upload it here?


Chuk

 

[ff168577]

I found this out the other day, there is another programming page that has to be accessed. It will limit the ranges for the squelch and the automatic alerting. I do not remember the programming info. I will find out. Where do you run in Bucks?

 

[kb4mdz]

OK, lets see if I can upload this diagram.


I have to dig up the part number for the opto-coupler; missed putting it on the visio diagram.


Some of the description is on the image, but other items like:


Radio is programmed for Turn-on/off with ignition only; again, so that if DC power drops, then comes back, radio wakes up.


The TX-1A matching transformer is from RDL Labs (RDL Homepage) & is used to go from the balanced, floating (they have DC voltage on them) speaker leads to the unbalanced (RCA plug) input on the audio amplifier.


The relay is a little spendy (forget the retail price, but it ain't cheap), but needed that one to run it from the 12VDC supply that the radio uses, and provide isolation. Certain variations of that relay model series don't have the isolation between coil ground & the Trigger Input ground pin, #6; prototypes behaved very badly. But it's important that the output side of the opto is wired to the relay trigger input just this way; Pin 5 outputs several volts DC (again, can't remember how much I measured during initial design steps).


One other aspect of that particular relay is the trigger inputs 5 & 6 can be remotely controlled by contact closure at a distance up to 75 ft. of wire. Which was helpful in some of our installations because the relay was in the electrical equipment room, one or sometimes 2 rooms away. You can then run low-voltage wiring to the relay, rather than running high-voltage (120/240VAC) from the breaker panel back to the relay, which most places would require conduit.


Details at Square D's website on that series of product. So I just simulated the 'contact closure' with a saturated transistor.


Also, other set of contacts in case there is a wild idea that floats up to activate something else when an alert comes in; Bay door? Flashing Light? Bed-turner-overer for those crew who just cannot be woken up? As was said in engineering school, that exercise is left up to the student.....


Audio amp is just using the standard 70V output lines; that way, adding speakers you don't have to recalculate impedances & maybe rearrange your wiring. I Don't know nothing about birthin' no 'zoned PA systems'; one zone, multiple speakers, tapped at wattages appropriate for location; Day room, apparatus bay, dorm(s), and maybe Kitchen, and possibly back patio where the grill is. (This is North Carolina after all; the grill can get used 12 months a year!)


It's been my experience that if you put most of this in a lockable cabinet, you can alleviate the 'fiddle-fingers' of someone who doesn't like how loud it is. The captains get final say on audio levels when you put it in. Again, with the CDM series, alert tones can be adjusted in programming for levels above or below the dispatch audio, escalating, etc.


When I find the part number I used for the opto package I'll post it on an updated diagram.

 

[kb4mdz]

FYI to anyone studying the station alerting circuit I published.


I keep forgetting to look up the actual part I used for the opto coupler, when I'm at the work pc. But I'm pretty sure it's the Optek OPI264 device. The package is right. I built the opto, and the 2 resistors into a package and encased it all in heatshrink tubing, with the input & output leads color coded as I put in the diagram; Pin 13 out of the radio is Orange, signifying Switched Battery +, meaning it comes on when the radio is turned on. Pin 4 is Brown, as a Switched Output, active Low. The opposite side, going to the relay trigger; Pin 6 of the relay is Negative, compared to Pin 5. I forget the exact voltage on 5, but it must be somewhere in the range of +12 V, in order for me to have used 1Kohm resistor in that side of the opto-coupler anyway.


That model of relay, 9050JCK25V36, is part of a whole family made by Square D; I used this one for the 12VDC coil which let me run it off the same power supply as the radio (Pin 2 is 12V+, pin 10 is Ground), and there is also isolation between pin 10 & Pin 6; some previous attempts before me use the 24VAC coil, and that does work on 24VDC, which was available in one station. But it caused other flakey problems. So I just simplified the design by saying it must all run on 12VDC, and lost any 24VAC/DC oddities.