Narrow Band versus Wide Band Tx range diferences ????

[Satelite]

Hello All:
I have asked this qestion once before but again im being told by other radio service shops this below .
With an already up and in operation for many years at wide band specs the tower had for example 35 miles range.
But when they converted to narrow band with the same hieght wattage and coax and atenae being the same other than now 12.5 khz narrow band they are experiencing a 10 to 15 percent reduction in tx range than before at 25 khz wide band.
Im not real close to exactly what got changed and how or with what as for the transmitter and reciever at the towers they are giving me this info from but was told tower /wattage / antenae / coax was all the same and just basicly changed from 25 wide to 12.5 narrow.
What is your experience with this situation ?
Are you losing range or the same ect ?
Would apreciate hearing any and everyones experince on this whether simplex or duplexed through a repeater tower or base to car or portable ect.
Please post in your reply what you have up as tp specs so i can at least attempt to make a comparison from before and after.
Thank you all and looking forward to your replies.
Satelite

[ard099]

I converted a wideband uhf system over to narrowband and it was very difficult to find any difference in coverage. The system had pretty good coverage to start with and if there was a loss in coverage it wasn't drastic. I believe if you have marginal areas in wideband, you are gonna really notice a difference in narrowband due to the fact that the noise level is the same but there is less audio in narrowband.

[d119]

This loss in coverage is to be expected. There have been many studies and it is a well known fact that the narrower the deviation, the less the coverage.

[wavetar]

Yes, a reduction in range in the 10% area is a definite known side effect of analog narrow-banding, and it was gonna be worse when 6.25 was to be implemented, so it's one of the reasons for the switch to digital...range is essentially unaffected or even enhanced with narrow/very narrow digital compared to 25KHz analog.

[Bill_G]

RF is RF is RF. There should be no change in range. I know the pocket protector boys can prove on their slide rules that deviation affects the S/N ratio which in turn becomes perceived range based on overall clarity. That I'll believe. But, if the customer is depending on those last few miles, they need to address the system design. They've been working the fringe and getting away with it. Now that their S/N is reduced, they lost coverage they never really had. It was never good, and it just got worse. 35 miles losing 10 percent sounds like the fade margin is gone, and they need to make a new plan.

[wavetar]

RF is RF is RF. There should be no change in range. I know the pocket protector boys can prove on their slide rules that deviation affects the S/N ratio which in turn becomes perceived range based on overall clarity.

You are correct of course, but perception is the reality, and if it worked in area X before, they'll want it to work in area X today. Old SecureNet radios before XL had a 30% range reduction...sure the RF was still there, but other factors made the 'usable' range a whole lot less.

[Satelite]

Hello All:
First thank you on the replies.
Heres my qestions then assuming i do in fact lose too much range when i convert to narrow band.
My license is for one of my FB6C comunity repeaters that is licensed as IG = Business Pool.
Im pretty sure i can go higher with the antenae but being honest its probably not going to happen = but could if i got hell bent on doing it.
Ok im licensed at 75 watts and 300 watts ERPs.
Would the FCC allow me to modify legaly to a higher output and allow higher ERPs watts ?
And would this recover any of the lost tx range of the tower to the portables / mobiles ?
Then if i add a 25 db recieve preamp to the towers incoming signal from the portables / mobiles = gain the lost incoming range back to the tower ?
Assuming of course i dont run into desense issues.
The duplexer is a 6 cavity celwave 120 db isolation as i recall and rated at 250 watts input with Andrew LDF 1/2 inch hard line heliax cable to the antenae so im thinking im more than likely pretty good in eliminating the desense issues from the git go.
Its also topped off with a AS Base Comander 705 10 DB fiberglass antenae for additional info.
The license allows 35 watts from mobiles so was wondering if license modification would allow more wattage output to help in gaining range back to the tower if the preamp was not enough at tower.
Do any of these options sound feasible or am i just plain gonna have the loss due to not being able to put out the audio levels i was able to before on transmit ?
I do have its eigther 1 inch or 1 1/4 LDF Andrew hard line ( Have took to see which it is i have ) that i could swap the 1/2 inch out with but thinking im not going to really improve anything by doing that because the antenae is up on a structure that kept the 1/2 inch feed line run at 100 ft or so anyway.
So it probably wouldnt have much loss in db in that 100 ft of run and wouldnt gain much worth while at going to the larger cable .
Or am i wrong on that one ?
Dont recall the calculations now what the wattage had to be set at from the repeater to stay at 300 watts ERPs but recall it being much lower than the 75 watts per license to stay at 300 ERPs so yes i can turn up the wattage on the next unit if i can modify the license to allow it.
Your thoughts please .
Any other ideas im missing out on to gain the range back other than going digital ?
What do you people have in your grey matter for ideas that i havent thought of ?
Thank you.
Satelite

[k2hz]

I don't beleive the FCC has changed any technical standards on ERP for narrow band.

It would take at least 3db increase in power to make any perceptible change in the received signal quality. More would be needed to make a significant improvement. TX power increase is not usually a practical solution and it is not an option with the portables.

A RX preamp helps to overcome feedline and duplexer loss but it will not help a signal that has poor SNR at the antenna. In most cases it will cause more problems than it solves.

The bottom line is that narrow band degrades signal quality to a degree very noticable to users in areas that were not "full quieting" before. This is what happens when politicians write technical standards to try to create "more" frequencies by ignoring the laws of physics. The advantages of FM decrease as the modulation index is reduced. The high band fiasco of creating 7.5 kHz spaced channels with 12.5 kHz bandwidth is beyond absurd.

NBFM Compandoring may be of some benefit but I have no experience with it. Digital has issues of its own but it is the only solution to make a signal fit 6.25 kHz bandwidth and it may be the better solution for 12.5 kHz.

[maxkelley_kc2spy]

I think we shouldn't discount the possibility of a preamp so quickly... They can provide some great performance if used properly, and you're not in an environment that will cause lots of overload to the preamp, and it's a quality device. I think the preamp would definitely help you recover the talk area that you had before.

[DavidJ]

Be careful, don't be too quick to answer this question. Many have reported that switching to narrowband results in a degradation of range, for a given set of radios; you can't argue with solid experience. It doesn't have to be that way, if you believe Shannon and Nyquist and information theory. The noise power in a 12.5 kHz channel is half that of a 25 kHz channel, but the information in an 11.3 kHz emission bandwidth is only 1.5 dB less than in a 16 kHz band. For this to work, however, the receiver filters have to be exactly half the bandwidth of the old ones and the LO and filters need to have half the previous frequency tolerance -- and the ones I've seen aren't. So, in the future if people really want to make narrowband analog work, they can -- without degradation in range. But it will require better receivers.

[Bill_G]

Be careful, don't be too quick to answer this question. Many have reported that switching to narrowband results in a degradation of range, for a given set of radios; you can't argue with solid experience. It doesn't have to be that way, if you believe Shannon and Nyquist and information theory. The noise power in a 12.5 kHz channel is half that of a 25 kHz channel, but the information in an 11.3 kHz emission bandwidth is only 1.5 dB less than in a 16 kHz band. For this to work, however, the receiver filters have to be exactly half the bandwidth of the old ones and the LO and filters need to have half the previous frequency tolerance -- and the ones I've seen aren't. So, in the future if people really want to make narrowband analog work, they can -- without degradation in range. But it will require better receivers.

Another way of saying this - it's model specific. YMMV.

[k2hz]

. It doesn't have to be that way, if you believe Shannon and Nyquist and information theory

That is true in terms of the capability of the system to transmit information but there are other factors in the quality of the received signal. A significant advantage of FM over AM is the quieting and capture effects which are a function of the modulation index (deviation divided by modulating frequency). As the modulation index is reduced to 1 or less , FM and AM become essentially equivalent. That is the case with the NBFM standard (2.5 deviation/ 3 audio) is a modulation index of 0.83. The modulation index for 16F3 was 1.67 (5 deviation/3 audio). The old 36F3 had a modulation index of 5 (15 deviation/3 audio) and was notable for outstanding quieting and clarity that was noticeably lost after the prior "narrow banding" from 15 to 5 kHz deviation in the 60s.

As DavidJ says, proper reciever IF bandwidth is a necessary step for optimum performance but the laws of physics still say a modulation index of 1 results in poorer signal quality than a higher modulation index that bring out the advantages of FM.

I think that our real word experince shows that there is a variation with reveiver design as Bill_G points out but there is some degree of degredation even with the best.

Comments I have hear from users are that absolute range where a signal breaks the squelch have not changed but fringe area signals are too noisy for reliable reception. I have found some need to tighten the squelch in CSQ systems since signals that used to be readable are now just noise.

I would like to know if anyone has experience with compandoring? Any system I am involved with has interoperability requirements that preculde use of a scheme that is not compatible with others.

[Satelite]

Hello :
Cant say i have any experience with compandering.
But motorola states in there M1225 brochure that the expand option in the m1225 and p1225 brings the rx audio back to 25 khz audio qaulities and even brags its better.
Qoated exactlty from the brochure:

X-PAND keeps a radio thats built to last 25 years from becoming obsolete in seven because you can switch to 12.5 khz and get the kind of audio quality you thought was only possible from motorolas 25 khz.
X-PAND technology actually compresses your voice at transmission.
At the recieving end it expands it while simultaneously reducing extraneous noise.
X-PAND technology at 12.5 can actually out perform 25 khz sound qaulity.
Available only in the motorola radius 1225 series.

Thats what they said back then when the 1225 came out.
Obviously other models may also have it as well since the brochure is old by today.
But i have really considered programming in the same freq into two 1225 mobiles the same wattage and antenaes ect with one ch being set at 25 khz wide and another set at 12.5 narrow specs and drive both cars till i loose the narrow band then switch both cars over to wide band and see if it recieves any better and how much if any range was gained ect.
But never got around to trying it so dont know what to think.
According to the M1225 reciever specs on uhf for sensitivy it states a 25 khz radio to be 0.30u and the 12.5 radio to be 0.35u which really doesnt seem to be enough diference in my mind to make much of any diference as to range for rx .
But a pre amp would if no desense issues make a noticable diference id suspect.
GEE WHIZ now i know why i like beer .
satelite

[DavidJ]

I think that our real word experince shows that there is a variation with reveiver design as Bill_G points out but there is some degree of degredation even with the best.

Comments I have hear from users are that absolute range where a signal breaks the squelch have not changed but fringe area signals are too noisy for reliable reception. I have found some need to tighten the squelch in CSQ systems since signals that used to be readable are now just noise.

Yes, and this is particularly the case when the receivers are not truly narrowband receivers. Unless the IF and audio processing filter skirts fit the actual bandwidth as closely as they do for "wideband" signals, there will be excess noise in the signal. And this is on top of the modulation index issue. Many of the newer Moto radios seem to have fairly significant audio processing, including steep lowpass filters around 3 kHz -- one way to improve modulation index would be to restrict the audio bandpass to only accept the audio frequencies that are actually being transmitted. Another way to load these YMMV dice is to play with the preemphasis and deemphasis curves.

I would like to know if anyone has experience with compandoring? Any system I am involved with has interoperability requirements that preclude use of a scheme that is not compatible with others.

This is another approach to the same problem of tailoring the audio to make the best use of available bandwidth. There's a fuzzy line at "compatible." We did some tests in the broadcast remote pickup (Part 74) world both on narrowband two-way channels (Motorola X-Pand and similar) and wideband program channels (Dolby, dbx, etc.) Don't assume that because it's different, it's incompatible. X-Pand sounds a little weird when received on a radio without it, but intelligibility isn't compromised in my experience. It doesn't sound any more weird than does a radio with highly tailored transmit audio, like a Motorola MX or a motorcycle radio with noise-canceling microphone.

The whole business of audio processing for two-way has been pretty much kept behind the curtain at Motorola and the other makers, and I think there's a lot of room for improvement. Systems that sound better are less fatiguing to use and produce better intelligibility. The P25 world has been bitten hard by this problem, because IMBE coders fail in the presence of high background noise. The same kind of improvements that make the job easier for the IMBE coder also help in the analog world, we just need to learn about and apply them. Motorola is doing a lot in this regard, for instance the dual microphone noise cancelling in the APX. It's a steep learning curve from where they were a few years ago, selling microphones with a low frequency rolloff as "noise canceling" when they weren't.

[RADIOMAN2002]

I personally didn't like to audio from a compandered analog Spectra. We have programmed all of our radios with all audio processing turned off. We have noticed no difference in range or clarity, just volume, as compared to our old Mitreks. A note on Motorola products is we have seen that in early versions of the HT-1250 built around 2003-4 with a Tanapa of PMUD 1482a the RX bandpass filters are not truely narrow, we can shove a 5KC audio signal through without clipping or muting. Latter and current versions will not pass anything over 2.75-3KC of deviation without clipping and muting.

[DavidJ]

I personally didn't like to audio from a compandered analog Spectra. We have programmed all of our radios with all audio processing turned off. We have noticed no difference in range or clarity, just volume, as compared to our old Mitreks. A note on Motorola products is we have seen that in early versions of the HT-1250 built around 2003-4 with a Tanapa of PMUD 1482a the RX bandpass filters are not truely narrow, we can shove a 5KC audio signal through without clipping or muting. Latter and current versions will not pass anything over 2.75-3KC of deviation without clipping and muting.

That's consistent with my experience. Too bad they are so secretive with what they are doing. There have been various versions of companded audio in Mot analog land: plain companding, similar to the A-law and mu-law used in telephony, Hear Clear (see http://batboard.batlabs.com/viewtopic.p ... 38&start=0) and others.

There's sort of a dividing line between radios with a hardware IF and fixed tuned filters (yes, I do remember changing out Permakay filters in Motracs at the tail end of the *first* narrowband transition) and the situation today where IF selectivity is done in DSP code and can be changed with a flash. Bottom line is, even before you do any audio processing the receiver bandwidth has to match the transmitted bandwidth or you will get clipping (too narrow) or excess noise (too wide). I am impressed with what Mot is doing in the APX with audio and IF processing. Hopefully they will get the message that not everyone is going to digital, and spend some more energy on developments that enhance the functionality of analog NBFM which will probably remain dominant in rural areas for a long time.