AAR Narrowband Migration

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tech020

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There are numerous technical issues that can affect narrow band range versus wide band FM. Frequency stability is much more important to keep the transmitted signal in the filter passband of the receiver. Just like the old cordless phones were static prone and not very good, the newer technolgy involving companders and digital signal processing can make up for the perceived shorter range. When tests were done on a county wide VHF-Hi siren encoding system using 300 baud ASCII tone signalling, we saw only a barely detectable 1db decrease in receive levels. Proper attention to marginal antennas is also important.
 

RRR

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Not quite "incorrect". Yes, I have read the studies, been advised of the research, and am pretty familiar with the theoretics of the narrower bandwidth, and why it should be "about the same" (or better??) and I understand why you claim what you do. -But this is just not happening here in the real world.

Same output power, same antennas, narrower bandwidth, now getting less distance than was had with 25Khz.

This applies to the HBD/DED units as well ("Defect detectors") those that could be once heard 15 miles down the track a couple of years ago, now are only able to be heard maybe 8 or 10 miles away at best. These are fixed locations, and this is noticed under all atmospheric conditions.
 

DrWhoVa

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Incorrect.

A 50 watt radio transmits 50 watts no matter if the transmission is wideband or narrowband..

Transmission range is not affected by a wide / narrow signal. Transmission range is largely dependent on any number of other things including the atmosphere, installation quality, location, etc.
How interesting since people in this area complain about not being able to hear anything that they could before narrowband hit. If that's the case, then IN THEORY things should be clearer, but they're not. And this isn't a very hilly area.

Around here if a train's right up on you, it'll blow you away, then you can hear it further out, but get the middle range (say 5-6 miles) and reception is crap. It's just how it is.

Plus there's several other things going on around this area that people say won't happen that I'm keeping under my hat. Suffice to say, it's not positive...
 

burner50

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How interesting since people in this area complain about not being able to hear anything that they could before narrowband hit. If that's the case, then IN THEORY things should be clearer, but they're not. And this isn't a very hilly area.

Around here if a train's right up on you, it'll blow you away, then you can hear it further out, but get the middle range (say 5-6 miles) and reception is crap. It's just how it is.

Plus there's several other things going on around this area that people say won't happen that I'm keeping under my hat. Suffice to say, it's not positive...
I didn't really notice anything when we switched.
 

tomfassett

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I agree with both sides... ;- )
Being trained in electronics and having to deal with RF in numerous jobs, it has been my experience that narrow band transmissions using the same power output from the RF transmitter is better. Most of my experience was with wireless microphones and when we switched to narrow band, life got a whole lot better (especially in crowded city centers).
That said, since the local railroads switched to narrow band, I can no longer hear the traffic in the yards (that are about 10 miles away) with a large scanner beam antenna 10 feet above the peak of the roof on my house. I used to have to deal with RF data links in a previous job and these things operated in the 1.2-2.3Ghz range so I became very observant of "line of site" issues forcing me to study potential blocks or interference sources in the environment. I have checked satellite data as well as driven the route looking for anything new in between the yards and my house but there is nothing of consequence that I can see. I have also talked to a few RR crew members I know and even though they had high hopes for the new handheld radios they insist the range is reduced. While listening on the scanner near the yards, I have heard a number of switchmen yelling into their radios because they could hear the locomotive but not the other way round (not that yelling has any chance of improving the RF output but frustration doesn't always support logic... ;- )
I just don't have a logical explanation for it but the problem really became noticeable after the switch to narrow band (and I verified the switch using a spectrum analyzer).
I remember some of our narrow band wireless mics had reduced RF power output and when I questioned the manufacturer's Rep he said that with a narrower band, they were able to reduce the power output which in theory reduced interference and harmonic interference problems with nearby sources. I haven't been able to check but are the new RR radios running at the same power output as the old ones? Other than that I'm stumped as it seems to be a chronic problem unrelated to atmospheric conditions, time of day or any other obvious effects I know of.
 

PJH

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I can only speak for my area, but we haven't had that much reduction in range. APCO and the FCC acknowledge that with narrowband you do lose some DB, but for most uses the range shouldn't be that noticeable.

One has to remember that with railroads, 99% of operations are simplex and preventive maintence isn't as rampant and that the radios take more abuse than most public safety operations.

I also think the switch in vendors to Kenwood and ICOM have something to do with it. Those where I am still using the MT/MTS2000's seem to suffer less than those issued the newer Kenwoods (TK280's and the NXDN units). Now I am not the greatest Kenwood fan and they are not all junk, but that's what we have been finding here.
 

tomfassett

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Unfortunately, I didn't ask what radios they are using now. I know they lost their old "clunky" metal bodied radios because one guy said the new lighter ones didn't pull his pants down as bad... ;- )
I do agree with the maintenance observation. I have seen even newer radios with a frequency drift issue (checking with the freq analyzer). I thought that was nearly impossible with modern equipment.
To add to my previous observations, the signal is rock solid on my mobile scanner up to about 5 miles then it starts deteriorating much faster than it used to. I have no explanation as to why it is better than it used to be near the yard but worse than it used to be further away. And that applies both to my base unit and my portables.
In an interesting aside, I can hear the Copper Basin Rwy traffic as well as ever and their repeater is further away than the UP repeaters. I can hear CBRY traffic clear as a bell on my mobiles even 60 miles away. I talked to a buddy who works there and he says he is pretty sure they have not changed radios. He says his cab radio is the same as he has always had (with all its dents, scratches and rust).
That just adds fuel to the "old vs new" argument. If it was a bunch of crotchety old guys trying to hang on to their old equipment vs a bunch of young techies wanting the newest and the best I would be more dismissive but it is the young guys who wanted tbe new radios that seem to be complaining the most. I'm stumped.
 
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