Minitor Pagers & Narrow Band

[bigdoggg]

I would like to know if anyone knows if the Minitor II, III, and IV pagers will work on the new VHF Narrow Banding. I have been told that they will not work but I do not see how they would not work. If I understand Narrow Band right, it only changes the TX. Not the RX. Or am I wrong about that?
I hope the Minitor II pagers will still work, for I love that little pager.

Thanks,
BigDoggg

 

[SteveC0625]

I would like to know if anyone knows if the Minitor II, III, and IV pagers will work on the new VHF Narrow Banding. I have been told that they will not work but I do not see how they would not work. If I understand Narrow Band right, it only changes the TX. Not the RX. Or am I wrong about that?
I hope the Minitor II pagers will still work, for I love that little pager.

I've been accumulating information on that exact question and have some of it drafted into a much longer discussion of the issue. Here is my info to date:

There are mixed reviews so far on the performance of wideband pagers in a narrowband world. The best I can learn is that there will be approximately a 10% reduction in output audio of a wideband pager receiving narrowband transmissions. There may also be a similar reduction in coverage in the fringe areas of some systems. But, when new narrowband channels come into use next to existing channels, wideband Minitors will likely begin to experience cross-channel interference or bleed-over. This may well mean that tone alerting could degrade significantly if the pager is hearing stuff from immediately adjacent channels.

I am sure the tech guys can offer a more detailed explanation of the why's, but in short, a receiver is supposed to be "tight" enough to ignore signals on either side of the frequency to which it is tuned. The II's, III's, and IV's are set to deal with channels spaced 25 Khz. apart. When the signals become 12.5 Khz apart, there suddenly becomes lots of room to the left and right of each frequency which the wideband receiver can still hear. Stick a new narrowband channel next to the former wideband channel and the wideband receiver is no longer precise enough to ignore the new adjacent signals.

There are some other technical issues that arise because of the change in channel spacing and width. I don't understand them very well myself, but I do know that they help to make all of this a bit of a crap shoot depending on where you try to use a wideband pager. Some places may only see the minor loss of audio and fringe reception. Others may see all kinds of interference, missed pages, false trips, and more.

From what I can learn, voice transmissions will not appear to be degraded very much in some circumstances. It is the tone alerting affected by adjacent channel interference that may cause problems first.

I am helping some neighboring ambulance squads get ready for the switch to narrowband. Nobody wants to trust a wideband pager in the narrowband environment for use by responders

 

[davidgcet]

the above is correct except that the audio reduction is more like 50%. wide band modulation is around 4.5khz, while NB mod is <2.5khz. so you have rouhgly HALF the audio over the air and therefore the WB rx can only amplify it to half volume. also the tones will drop from 3khz to 1-1.5khz, this may or may not alert the pager. most will alert just fine, but some(usually problem units) dang near require 3khz to open.

the audio problem is really not an issue unless the person is in a high noise area. the adjacent channel use will be an issue if someone gets a slot next to you on either side. you could in theory have 3 adjacent channels in a row, yours and 2 others(1 above your freq 1 below it), which would come thru the pager or at the least severely degrade it's range. odds are that in highly congested areas this will happen much sooner than rural locations with plenty of existing VHF slots available.

 

[SteveC0625]

David, my 10% figure came from several overview presentations by consultants to the industry. I am surprised that they are suggesting such a low percentage of audio reduction will occur compared to your numbers. I suspect that it is going to be a wait and see approach regarding using existing wideband pagers.

As I stated previously, fire and ems agencies around me are not taking a chance on missed pages or lost info. Everyone I talk with is definitely ordering narrowband pagers.

 

[davidgcet]

it really depends on the unit, some have more audio than others and therefore the difference is less noticable. but the signal coming to the unit is half the amount it was in WB, and therefore takes 2x the amplification to bring it back to "regular" levels. most folks don't run a pager at full volume, so all this means is turning it up another notch to two to get close to original. if you say the volume has levels 1-10, many people run it somewhere between 4-6. they may have to turn up to 8-10 to get the same volume level out of the unit. so there may be only a 10% difference in loudness with the volume turned up more, but it is closer a actual 50% difference. again though, that depends on the units in question!

 

[yankeephill]

Minitor II pager and narrow band.

Minitor II pagers wiil work on a narrow system and as far as the receiver goes, I have converted Min II's
to narrow band Rx for 12.5 K spacing with GREAT results.

 

[SteveC0625]

Minitor II pagers wiil work on a narrow system and as far as the receiver goes, I have converted Min II's to narrow band Rx for 12.5 K spacing with GREAT results.

An interesting claim, and hopefully one that will work in a wide variety of situations.

Perhaps you'd tell us how you do it so that more of us could experience similar results?

If anyone can offer up techniques to adjust III's and IV's for NB operation, it would be equally appreciated.

 

[yankeephill]

Change the I.F. filters.

 

[NCFire11]

The audio output of a wideband pager on a narrowband system is not as bad as you think. It really just sounds like the audio is more "distant." The reduction is not that much in my opinion, definitely not 50%. The 10% statement is more accurate.