Wide band vs narrow band

[N4KVE]

Suppose I take 2 modern day radios, capable of narrow band. I set them up to tx & rx on ch 1 @5kc. Ch 2 tx & rx @ 2.5kc. Will they sound the same from 1 ch to another. I remember when I was a kid, & my friend's father owned a taxi with a Motorola Business Dispatcher. Real wide band. 15kc. Listening to the dispatcher was like Hi Fi broadcast quality. So any difference between 5kc & 2.5kc? GARY N4KVE

[Bill_G]

No. sounds exactly the same.

[N4KVE]

Thanks for the reply. GARY N4KVE

[Bill_G]

You're welcome Gary. Theoretically, a narrow band transmission would sound half volume in a wide band receiver. Since all modern two way products are capable of both, manufacturers compensate for the lower deviation on a designated narrow banded channel with more gain in the audio circuits so that the users do not have to ride the volume control as they switch or scan between channels that may be operating differently. As long as the radios are programmed correctly, there is no noticeable difference. OTOH, a wide receiver will hear a narrow transmitter as low deviation, and a narrow receiver will hear a wide transmitter as loud or distorted. And people do make mistakes in programming when adding radios to an existing system.

[JD]

Also keep in mind, you will not have the same area of coverage, 20 to 30% reduction. The audio sound the same but customers do not understand why the radio do not work very well from certain locations as before.

[N4KVE]

Also keep in mind, you will not have the same area of coverage, 20 to 30% reduction. The audio sound the same but customers do not understand why the radio do not work very well from certain locations as before.

So the narrow band transmission will have less range? GARY N4KVE

[Bill_G]

YMMV

Range is range is range. Some people say it is the same. Some say it reduces.

[RadioSouth]

How about when the two different bandwiths are mixed ? I'm using a Spectra to monitor a few channels that will be going to 2.5 KHz
will it sound reasonably OK when the changeover is made ?

[Thomas]

How about when the two different bandwiths are mixed ? I'm using a Spectra to monitor a few channels that will be going to 2.5 KHz
will it sound reasonably OK when the changeover is made ?

It was mentioned above what happens when the two bandwidths are intermingled. Go back a few post and read what Bill_G posted

[AEC]

I suspect the term 'range' is somewhat simplified in certain respect.
Given a 5kHz deviation can be 'heard' farther than a system with 2.5kHz. deviation, all things being equal, of course.

It all boils down to intelligibility...Minimum noise floor requirements, receiver sensitivity, site location and coverage of same; it all plays into the equation.

[Bill_G]

Yes, for sure s/n plays a part in intelligibility. For some people that translates into apparent range. The rf level remains the same. All other things being equal, the range should not change between a 25kc channel and a 12.5kc channel. But, when they are working the fringe where s/n is critical, noise usually wins unfortunately. The customer will have to play with loss and gain to recover that last mile if it is important to them.

[AEC]

No single site system can cover a geographically large area 100%, but many assume this is possible for some odd reason.
I was testing one of my 460 machines after tuning, and drive tested it, with the antenna at about 30' AGL, I could access it, and hear the reply on my portable, but the audio was not comm. grade, just 'usable' at best.
I never expect a ground based machine to cover a vast territory, only a few miles is the best one should hope for.
Mountain sites are a different matter altogether, and I found that even a modest radio can easily hear out past the 80 mile range from the site.
A fact we have noted on several expeditions to CA. border from the Phoenix/Mesa city area.
This machine is located on Signal Peak, in Gila county, AZ. and has been a superb performer that SAR groups now coordinate on it regularly, as others in the same locale fall far short of the coverage(even south mountain).
Of course, wwhen your antenna is sitting at 8,000 feet ASL, you do have 'some' height advantage, not to mention a super receive location to boot!
Talk out and receive has always been wonderful, and thanks to a location that is NOT RF polluted like South Mountain is, it is easily worked from great distances, like Tucson to the south, and Payson to the north, but also includes Show Low and many other places around the state,
Nobody should ever expect to have a 40 mile radius to work with if your antenna isn't above the RF flotsam and jetsam of a cityscape.
Proper tuning and a senstitive receiver play major roles here.
Not to mention selectivity and adjacent channel rejection.

[KE7JFF]

You know, I have been somewhat skeptical about the range going down with the switch to narrowband. I know the USFS here in the Pacific NW at certain sites which have switched to narrowband, the rangers claim their range and fringe areas have changed when they flipped over. I've listened and it sounds great for the most part; the fringe areas sound to me like maybe more of a mic gain issue.

[RadioSouth]

The FCC has a FAQ on narrowbanding and they mention that narrowband compliance may result in a 3dB loss of signal strength (with all other factors remaining equal).

[Al]

Jacobsmeyer published an article in April 2010 Urgent Communications stating that FM theory can be used to predict how narrowbanding will affect system coverage. From that article:
"The important principle illustrated by [figure 2] is that loss in coverage is strongly dependent on how well the service area is currently covered. For example, if 90% of the service area is covered with an adequate signal to noise ratio today and the total loss in S/N due to reduced deviation is 6 dB, then the coverage loss will be 26%. However, if 99% of the service area is adequately covered today, the coverage loss is only 4%."
The above would seem to corellate with the reports that list "no reduction" and "20-30%" reduction(everybody's right). Reduction depends on how well your service area using 5 Khz deviation is covered today.

[xmo]

Jackobsmeyer made a fundamental error in his analysis - he overlooked the 3dB reduction in the receiver's noise floor due to the narrower IF bandwidth. Therefore, the actual reduction in system performance that results when migrating from wide-band analog [+/-5 KHz deviation system] to narrow-band analog [+/-2.5 KHz deviation system] is 3 dB.

This figure [3dB] is the value given by APCO staff in their narrow-banding presentations.

I realize the temptation to say "signal is signal". Yes, it is - but only with respect to the carrier. So, in fact, migration to narrow-band will not result in a lower signal level [carrier] at any point in the coverage area than there was previously, but a carrier conveys no useful information, modulation does that. That's where concepts of modulation index, SPD, DAQ, etc. come in.

Those looking for an in-depth technical explanation should refer to the EIA/TIA TSB-88 document series.

[Bill_G]

And 3db is not so significant that the system users will report loss in coverage. In my experience, most users think the radio system works terrible. Nothing will change for them. (big grin)

[resqguy911]

You know, I have been somewhat skeptical about the range going down with the switch to narrowband. I know the USFS here in the Pacific NW at certain sites which have switched to narrowband, the rangers claim their range and fringe areas have changed when they flipped over. I've listened and it sounds great for the most part; the fringe areas sound to me like maybe more of a mic gain issue.

The devil's advocate in me wonders if a placebo test were done, ie: tell someone you reprogrammed their radio, but actually change nothing, would they report back with varying performance reports post "reprogramming"? Kinda like an RF sugar pill...

[KE7JFF]

The devil's advocate in me wonders if a placebo test were done, ie: tell someone you reprogrammed their radio, but actually change nothing, would they report back with varying performance reports post "reprogramming"? Kinda like an RF sugar pill...

Its possible; i'm not responsible for their programming, just actually an authorized user, but I think I know who I can ask for that answer.

Though, I think Bill_G might know more than I do...

[xmo]

Will users notice the change after a system is narrow-banded?

Maybe - maybe not. The fact is that many systems have adequate signal margin to withstand the impact of narrow-banding with no noticeable effect. But does 3 dB matter? It sure can. Especially for systems that are already coverage challenged.

Look at it another way. If you have a radio on the bench that's supposed to put out 100 Watts and you're only getting 50 do you put it back in service? [why worry, 3 dB doesn't matter anyway] If you have a radio with specifications that say it is supposed to have 12 dB SINAD sensitivity of -117 and all you can get is -114 do you give that a pass? No? I wouldn't.

3 dB can matter. A 3 dB drop in signal level is sufficient to take a received signal from 12 dB SINAD [readable with difficulty] down to 1 dB C/N [unreadable] or to take a received signal from 20 dB quieting down to 12 dB SINAD. That is a very noticeable degradation in DAQ [Delivered Audio Quality]

DAQ is a metric that has been used extensively in radio coverage prediction and verification. It is a scale that runs from 1 to 5 with 1 being unusable [speech present but unreadable] to 5, which is perfectly readable with negligible noise. 12 dB SINAD represents a DAQ of 2.0, which is readable with difficulty. 20 dB quieting [about 17 dB SINAD] represents DAQ 3.0, which is commercial quality audio, readable with only a few syllables missing.

Further information on DAQ and the relationship of signal levels and BER to DAQ for the common analog and digital land mobile channel formats is found in TSB-88, must have documentation for system designers, RFP writers, and anyone attempting to master the art of land mobile radio.

[Bill_G]

3db equipment failure and 3db increase in path loss are different. One is an indicator that more problems are on the way. The other is normal. But, your point that challenged systems might need 3db is the crux of the misunderstanding about how narrowbanding will affect users. Any system that needs the 3db is already in trouble just like the broken radio on the bench.

[Al]

xmo, I'll disagree with you on one point that you mentioned above: switching IF filters from wideband to narrow does not change the receiver's noise floor - that's set by the active device in the frontend. Switching does reduce the noise allowed through the IF filters by 3 dB if the shape factor of both filters is about the same.

[xmo]

Don't confuse Noise Figure with noise floor. The use of the term "receiver noise floor" is correct in the context of this narrow-banding discussion.

Although Noise Figure is determined by the receiver's front end [among other things] it is bandwidth independent, hence for a given receiver design - changing from one bandwidth to another changes the N part of C/N in direct relation to the change in bandwidth.

[N=kTb , thus N varies directly with b]

TSB88 defines [Inferred] Noise Floor as: "The noise floor of a receiver calculated when the Reference Sensitivity is reduced by the static Cs/N necessary for the Reference Sensitivity. This is equivalent to kTb + Noise Figure of the receiver."