Batboard

ok, this is a problem that i've just become aware of:

our buildings use some type of piezo siren that honks an incredibly loud and annoying pulsing type tone in an on-off-on-off format (almost like a police whistle on steroids) coupled with a flashing strobe light. if you've ever been in any commercial buildings when one of these things went off, you know exactly what i'm talking about.

problem is, when one of our staff is transmitting from a portable unit, his audio is muted while the alarm pulses. i'm able to receive the words or syllables that he says 'between' alarm pulses, but everytime the alarm sounds another blast he gets muted.

is there anything in the audio circuitry that mutes the mic when audio input is 'too loud'?

...or is it possible that an incredibly loud audio signal will over-deviate the signal causing it to be unable to be received?

...or is it possible that the piezo is generating some tones in the 134.3 Hz range that causes MY radio to mute?

...or is it possible that the piezo is generating some type of RF interference that causes the radio to have problems modulating the carrier?

i know these are some wild scenarios, but i haven't had a chance to do a live-test to see if i can narrow it down at all. i just thought i'd throw this out there to see if anybody is aware of this and perhaps steer me in the right direction.

thanks

...or is it possible that an incredibly loud audio signal will over-deviate the signal causing it to be unable to be received?

BINGO

This exact scenario was the focus of a student's thesis.

Read this thread:
http://batboard.batlabs.com/viewtopic.php?t=26870

Actually, it may not even be making it to the TXer... if you're running AGC, he'll be "muted" when it goes to -100dB to deal with the siren noise.

Bone conduction mics (ear mics, or possibly throat mics) *might* solve your problem.

I can use my noise-cancelling mics in pretty loud situations (standing next to fire apparatus in pump gear) with my XTSs. Of course, that's constant noise... periodic noise is a bit trickier.

WOW!!! the way he described it is exactly the same problem i'm having. i haven't gone into the field-test stage yet to see what's actually going on, i'm still in the "literature review" as he puts it. however i think we can rule out some of the causes by comparing what is common or not common to both of our systems.

for example, he's voted, i'm not. as a result, he has telco lines in his system, i do not. he uses speaker-mics, i do not.

like him, i'm also using DPL

my system is simple. UHF (451/456MHz) repeater consisting of a zetron-38a tone panel, and an MTR2000. portables are HT750's. i believe AGC is disabled, but i'll have to check the codeplugs to be sure.

as in the other case, my audio drops but the carrier does not. (as far as i can tell by listening by ear to my portable)

from what i read, it does sound like an over-deviation problem. i'll have to listen to the portable's TX frequency to see what's going on there. kinda wish i had a service monitor. :/

i guess i'll try the radio with different mic-gain settings to see if i can get audio to pass. depending on how low i have to set the gain, i don't know if that would be considered a solution. if i can solve the muted audio problem, but now the guy has to scream at his radio all the time, that seems a little less than perfect.

in the meantime, let's assume that my portables are transmitting audio (perhaps a little distorted) just like his were, and i can receive it with another portable. this would then make it the repeater's fault for not passing the audio.

would it be practical to make any adjustments to the MTR2000 so that it would pass an over-deviated signal? would this cause more problems than it fixes?

btw - where's that thesis he promised!?!?!

Just so you know what exactly it is you're dealing with, the NFPA
signalling standards require a MINIMUM of 85db at TEN FEET from
the signalling device. Notice that this is a minimum and it is common
for audible signalling devices to exceed this level, often by a rather
large amount. Depending on the sound actually being generated, it
can really be painful and objectionable which is what it's actually
designed to be, sleeping occupancies being the best example.

Also, note that in usual audio system terms the db rating of a device
is commonly measured at something between one to three feet, and
the FA devices are measured at ten feet. Use your imagination to
figure out what the one to three feet rating for these things must
figure out to be!

It's no wonder at all that the person using the portable is having
his audio overdeviated by the sound of the signal.

440roadrunner wrote:

...or is it possible that an incredibly loud audio signal will over-deviate the signal causing it to be unable to be received?

BINGO

....Yes!

Simply Yes!... the brain is blocked and it does not listen when the sound is very strong in high frequencies.

Regards

eboe wrote: in the meantime, let's assume that my portables are transmitting audio (perhaps a little distorted) just like his were, and i can receive it with another portable. this would then make it the repeater's fault for not passing the audio.

Yes, I'd say that's likely the case as it was in his. You can confirm it easily enough with a portable as you say.

eboe wrote: would it be practical to make any adjustments to the MTR2000 so that it would pass an over-deviated signal? would this cause more problems than it fixes?

The setting I'd look at right off the bat is 'analog boost'.

The analog boost is enabled by default IIRC. It can take an already over-deviated signal & pump it up even more...possibly to the point the portables can't demodulate it.

I don't recall off-hand if there's any type of 'noise reduction' setting in the MTR. If there is, you could play with that too.

Todd

I would also be willing to bet that the repeater throughput audio setting is well into compression. This also adds to the problem. If you go back a search this site, there have been a multitude of threads on setting repeater audio levels. Most radio shops don't have a clue how to set it correctly.

Your probably seeing the results of both the portable audio setting adjustments, the repeater settings and maybe some off frequecny issues as well. If you can get your hands on a service monitor, it will make your life so much easier to resolve what your describing as a problem. You will have to start at the repeater, check it out completely and then move on to the portable. If the repeater receiver is off frequency, this will also cause it to be more prone to chopping a high deviation signal.

Good luck.

Jim

eboe wrote:ok, this is a problem that i've just become aware of:

our buildings use some type of piezo siren that honks an incredibly loud and annoying pulsing type tone in an on-off-on-off format .

problem is, when one of our staff is transmitting from a portable unit, his audio is muted while the alarm pulses.
...or is it possible that an incredibly loud audio signal will over-deviate the signal causing it to be unable to be received?

thanks

Are you using MDC at all? If so, it could be tripping the Data Operated Squelch....

When operating full-duplex on the amateur band, feedback will sometimes trip the data operated squelch on my Spectra, causing it to mute...

I've never had that problem. I use a mix of ht1250, and a mix of radius.
We also have crappy Icoms, and Vertrex. We also use sholder mics too.

Oh, and we have a repeater.

However, we have had a problem with certain radios and bag-type cell phones setting off the alarms...

ffexpCP wrote:However, we have had a problem with certain radios and bag-type cell phones setting off the alarms...

You mean like press transmit and it trips the fire alarm??? I'm assuming the RF is pissing off the electronics in an addressable smoke detector or something along those lines? Never seen that happen before.

Yep. It was weird. This was in my old dorm. It would trip the horns in the unit but not the strobes. All the smoke detectors (household-type) in the unit were interconnected, but independant of the alarm system, so nothing would show up on the FACP. It would only trip the horns in the unit, not the horn circuit. The system was a hack job anyway. They finally replaced the main panel.

Anyway, come to think of it- ANY old analog cell phone would set it off. If it was digital nothing happened. I can't remember how it reacted to 800 MHz public saftey radios though.

It was an Edwards system if that matters.

ffexpCP wrote:Yep. It was weird. This was in my old dorm. It would trip the horns in the unit but not the strobes. All the smoke detectors (household-type) in the unit were interconnected, but independant of the alarm system, so nothing would show up on the FACP. It would only trip the horns in the unit, not the horn circuit. The system was a hack job anyway. They finally replaced the main panel.

Anyway, come to think of it- ANY old analog cell phone would set it off. If it was digital nothing happened. I can't remember how it reacted to 800 MHz public saftey radios though.

It was an Edwards system if that matters.

Alright. That doesn't make ANY sense whatsoever but ok.

Around 1980 I was a regional manager for Kidde and we sold a fire alarm control panel called a KDR-1000. There were a LOT of these things sold all over the country. The panel had plug-in zone modules and plug-in alarm circuit modules. I had an eight-zone panel in my basement, all up and running fine, but when I would key my 200-watt HF transmitter the stray RF would activate every module on the panel. They were not locked in, however, and when the RF ceased the modules returned to normal. I remember wondering if any of our dealers had ever sold the panel to any kind of transmitting facility, and what happened when they put the power to the panel. The panels were second-generation solid-state units but they were nevertheless almost completely unprotected against stray RF.