I was wondering if you guys have had any problems with other frequencies bleeding over onto your minitor I's or other minitor's. I have a low band minitor I and Ive been getting interfence from a high band cab company frequency coming over on my pager. Any reasons to why this is happening?.
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Thread: Minitor I Question
09-30-2001, 11:14 AM #1
- Join Date
- May 2001
- Truxton, New York, USA
Minitor I Question
09-30-2001, 03:29 PM #2
There are three types of intereference commonly seen in the fire service
Skip -- common on low band, where radio signals propogate (travel) unusually long distances. In this case, that's not the issue since we're dealing with two different frequencies (low and high band)
Harmonics -- A radio signal will cause interefence to receivers at 2x, especially commonly 3x (and sometimes even higher multipliers) frequency. So a transmitter at 156.600 will cause interference on 469.800 (I'm pulling numbers out of thin air so they may not be actual "frequencies" we use). There's other details to this, but that's the basics -- search the 'net for "Radio Harmonics" or something like that for more info. This isn't the problem as they don't work going down -- so a higher frequency (the cab company) won't have a harmonic that interferes with the lower frequency (pager).
Intermod -- which is what we have in this situation. Another frequency is being picked up and amplified by the pager tuned to a different frequency, indeed a different band. Intermod is short for Intermodulation which is a radio receiver picking up a signal on another frequency (modulation). Almost definitely the Cab company has a radio transmitter near where you pick up the interference. Many, many different things from that's just the way it is to a corroded part to wow, that's neat could be allowing the strong signal to come in on the pager. With all the possible sources of intereference, sometimes all you can say is it's amazing radios work at all.
Skip & Harmonic are simply the way radio waves work and there isn't much to be done about it. PL (private lines) can be a work-around to minimize disturbance, and filters on the **source** might help harmonic interference.
Intermod is caused predominantly problems with the receiver -- with the age of the Minitor I, it probably has corrosion, etc that's making it more susceptible.
[ 09-30-2001: Message edited by: Dalmatian90 ]IACOJ Canine Officer
10-02-2001, 07:08 PM #3
- Join Date
- Mar 2001
I had a Minitor II for 10 years. We use to be on 39.98mhz. (low band) We got the California Air-Quality Authority EVERY DAY for years. It was like your whole district's tones going off for 10 minutes everyday. Now we've moved to 460.*** and things are great. We have added a silent PL tone. This PL tone must be heard by the base transmitter, or you wont hear a thing. This filters almost all skip.
As for the new pagers. I think the Minitor II was the best. The new III's we have are junk. I lost a knob in a week. The other in weeks after. We now have guys missing calls they never heard. It's way overpriced and they arent any better. Now over 50% of our FF's carry their old Minitor II's.
[ 10-02-2001: Message edited by: DELBERT ]
10-04-2001, 12:27 AM #4
Yeah, the Minitor II's a pretty much junk. Had the same problem with knobs..took so long for them to get the parts the lasttime I turned mine in I sinply wrapped the stud in electrical tape when i lost a knob the other week. The Minitor II's were good...but I still say the original Minitors were the best. Sure they look like a brick, and weigh about as much...those things were plain tough. I dropped mine in a dump tank at a drill one time. I simply put it on the defroster and dried it out....to my knowledge it still works today.
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