Narrowbanding Range

[jfhtm350]

Is it just me or does it seem like the narrowbanded frequencies dont get out as good as they did when they were wideband. Sometimes I wonder if the ctss or dc code is not getting decoded or getting cut off too when I program the scanner for NFM. When I program them to NFM it seems as though it just amplies the sound because the background static gets louder with the voice.

[ka3jjz]

There is a possibility that the folks that have narrowbanded reduced the output power of the transmitter - that would certainly account for this. Otherwise, no clue....Mike

[N9JIG]

One of the issues with narrowbanding is that there is a slight decrease in range in many instances. In our system areas that were problematic before are slightly worse after.

[Ed_Seedhouse]

Originally Posted by N9JIG

One of the issues with narrowbanding is that there is a slight decrease in range in many instances. In our system areas that were problematic before are slightly worse after.

When you reduce the deviation of a frequency modulated signal while keeping the amplitude fixed, you put out less total power, and this can effect range. Narrowbanding reduces deviation, but unless the radio is designed to compensate already it will likely keep sending at the same amplitude, thus reducing total power output.

[petnrdx]

The output power is the same wide or narrow. In the field you shouldn't measure carrier power difference.
Unfortunately, our ears are not listening to the carrier alone. Unless you are doing CW.
And I would not think people would have had any reason to reduce TX power in the narrow banding process. Unless they had to re-coordinate for some reason.
But, when you reduce deviation, you can loose some "delivered audio quality" or whatever term you happen to like. It seems like there are always people that want to nit pick terms or measurements.
Lots of discussions about this.
Depending on who you discuss this with, I have seen / heard descriptions of theory that differ from about 3 dB loss to about 6 dB loss.
Applying that "loss" to RF readability also varies wildly.
The method I believe in the most is reduction of 12 SINAD measured the way TIA recommends.
I ran a bunch of field "drive measurements" using test equipment and GPS mapping applications.
Just because I had to "show myself" something I could really measure.
Out of several drive tests of the same TX wide, narrow and P25, 20,000 "readings" that were from hundreds of thousands of measurements the instrument took, it always came out between 3 and 4 and a half dB loss under the same conditions near where I live. Not a way to characterize a specific system, but a way to compare before and after the SAME transmitter.
I do believe that other terrain, or buildings, etc. that it would vary a bit more than that.
And I believe that "weaker" coverage systems might vary more.
So, I think that finding a loss of 3 dB to maybe even 9 dB could occur in the DAQ if a system just did narrow band programming, and did nothing else to "mitigate" the expected loss.
I think a lot of system operators increased TX power, increased antenna gain, improved combining / multicoupling, and added things like RX pre-amps.
So, for example the place where I have worked for the last 12 years was able to improve coverage a bit.
Unfortunately, the systems where they were already pushed to the limit, are likely to be the ones that just didn't have the funding to make improvements.
And many of those probably were told they would not need to really carefully align their radio equipment.
I am sure finding that much more care to fine detail is needed at NB than it was at WB.
If a system you listen to were well below full system deviation at wide, then they went to narrow, you would notice it much more that if they were really at full deviation both times.
And a lot of people have found the PL or DPL deviation level to not decode well after NB.
Sounds like lots of systems that had good funding, and did the "due diligence" to really optimize are doing OK those that were "short" before have just gotten even a litter worse.
Lets hope in the next couple months more of that gets fixed.

[N9JIG]

Originally Posted by Ed_Seedhouse

When you reduce the deviation of a frequency modulated signal while keeping the amplitude fixed, you put out less total power, and this can effect range. Narrowbanding reduces deviation, but unless the radio is designed to compensate already it will likely keep sending at the same amplitude, thus reducing total power output.

Slightly off the original topic but here goes:

Is Canada going narrowband similar to how we are here in the US?

[jim202]

It is amazing to read the comments here on just what each individual thinks the answer is. Maybe it would be wise for everyone to stop for a bit and do some homework on the issues a radio system has when it goes narrow band.

One of the statements that I will make is that to the best of my knowledge, no system has changed their output TX power, no antenna systems were increased in gain and no antenna heights were increased to compensate for the range reduction that narrow banding a system causes. That would require a license modification and the problems that will come with it.

Think about this for a moment for all those that are believing that major system changes other than narrow banding was done. Any change in TX power, antenna gain or antenna height would cause that license to have to be run through a frequency coordinator for approval and then back to the FCC for the changes to be made to the license.

The frequency coordinators are in most cases requiring a lowering of transmitter power if any major changes are done to the transmitting system. With coverages not always being good to start with, do you think a user is stupid enough to get put into a position where they have to lower their power by 3 db or so? If they are smart, they won't change anything other than go narrow band. But it will cost them coverage. Sure they could add more sites, but that will cost money they don't have and time.

With that all being said, have at it. But do your homework on the subject before making statements that might not stand up to the real facts at hand on this issue.

[jfhtm350]

It only seems like a small difference in range to me but enough to notice its not the same. I am going by my experience from listening and not any tools or fancy meters. The longer distant stations that I can recieve are the ones that are most noticeable.

I had programmed my scanner to NFM for a few days (most channels with repeater codes) and noticed the audio cutting out. I go to the scanner and press Func+Tune to tune into that freq without any repeater code and they will be talking. I tried to do this many times when it happened to see if the repeater code was keeping the scanner from opening the channel. It sure seemed as though the PL or DC code wasnt getting recieved or decoded properly although I dont know this for sure as the reception wasnt always good at the time.

I have since given up on programming NFM and just programmed them all back to FM mode since it seems to recieve better for some reason. I do have to turn the volume up some but thats no big deal to me.

[Ed_Seedhouse]

Originally Posted by N9JIG

Is Canada going narrowband similar to how we are here in the US?

I don't know.

[Ed_Seedhouse]

Originally Posted by jim202

It is amazing to read the comments here on just what each individual thinks the answer is. Maybe it would be wise for everyone to stop for a bit and do some homework on the issues a radio system has when it goes narrow band.

You trying to spoil my fun? :-)

I'll admit that the transmitter power speculation was ill founded since, on reflection, it is fairly obvious that a transmitter that is putting out the same voltage and the same wattage is putting out the same power and there's nothing about a narrower bandwidth should affect that. The only thing that changes with narrow banding is frequency deviation of the carrier.

[bear780ks]

N9JIG i had a look at your shack photo's wow.! that's a fare size amount of radio equipment i would like owning just half of what you own.

My uncle was a Ham operator and had some of the old style ham equipment but he had the new as well but it's sad he's not here to enjoy it any longer as he passed on a few years ago.

But i wanted to pass that on to ya again, have a good Weekend 73's b780

[N9JIG]

Originally Posted by jim202

It is amazing to read the comments here on just what each individual thinks the answer is. Maybe it would be wise for everyone to stop for a bit and do some homework on the issues a radio system has when it goes narrow band...

Remember that this is a scanner board, many of the participants are not professional engineers, just folks with scanners wondering if narrowbanding causes range loss...

It is true that a majority of the systems did not change output power in fact or on the license, they just changed the emissions on the radios. If they did it right when they changed the actual radios they put the transmitter on a service monitor to check for proper power output, deviation, PL deviation, and making sure the radio is on freq among other things.

As the supervisor for our system, comprising 5 police dispatch channels, several tac channels and 12 agencies I can confirm that indeed there was range differences directly attributable to the narrowband process. Yes, the actual output power remained constant on each channel, in fact all of our transmitters the radios were the same, just reprogrammed for the narrower deviations. That in itself does actually reduce the signal's reach.

We did raise the output power of one of our dispatch channels later as a result of narrowbanding, we went thru the whole coordination process with approvals from co-channel users and the rest. This channel had some difficulties with talkout range after narrowbanding that were solved by going from 60 watts to 100 on the repeater. It had no talk-in issues so receiver sites did not have to be changed.

On a couple of the other channels we were able to relocate or raise the receiver antennas to compensate. This does not require any type of FCC approval or coordination but does require a financial investment. On one channel one area in particular talk-in was poor before narrowbanding and worse after, so we raised the receiver antenna in that area some 20 or 30 feet and that fixed that. Another area on the same channel as well as a nearby area on another channel that shared a receiver site (both receivers are in the same cabinet and share an antenna, it is right on the border of the two towns) had difficulties with talk-in that came up after narrowbanding. We relocated that receiver cabinet and antenna from a water tower to a new cell tower a half mile away. After smoothing out some grounding issues we were good to go.

As we narrowbanded each channel we had the techs put the transmitter on the service monitor and make sure it was in spec. Several of them were slightly off freq after narrowbanding and had to be tuned in a bit. Usually they were within spec but we wanted them dead on. Same for PL deviation, while for a scanner that really isn't required if it is too high or too low a radio might not make the repeater or a mobile might not open.

Another thing that was not done as much as it should have been was checking the mobile and portable fleets. While all of our radios were easily reprogrammed for narrowbanding some had deviation or frequency issues as well so we made a point of running them thru a service monitor when we could. We sent a few back to the Depot for work if they couldn't be set to spec in the field.

Once all this was done the systems sounded as good if not better than it did before narrowbanding. One of the issues were user complaints that the systems sounded tinny after narrowbanding but those complaints went away as they got used to it. Narrowbanding gave us the opportunity to simultaneously go thru each system and make sure everything else was up to spec and we fixed a lot of other problems. When we were done each channel was in great shape and we were able to enjoy the fruits of our labor and investment for a while.

Narrowbanding tends to make marginal areas worse. If a system was slightly over-engineered in the first place then most of the time narrowbandings effects won't be noticed but if there were rough areas before they are going to be more noticeable.

[jackj]

One of the major determining factors for a system's range is the signal-to-noise ratio. Just as a wide window will let in more light, a wide system bandwidth will let in more RF. When you reduce the transmit bandwidth with narrow banding without reducing the receiver's window you increase the amount of noise on the signal. While the total transmit power does not change with modulation, the FM quieting does unless the amount of noise is reduced by the same amount.

A properly narrow banded system will have had the pre and de-emphasis circuits modified as well as the IF filter replaced in the receivers. Failure to make these changes will reduce the system's useable range.

The NFM setting on your scanner makes none of these changes. All it does is increase the audio gain to compensate for the reduction in recovered audio on a narrow band system.

[petnrdx]

I have the impression from others in the "infrastructure" part of the business ( meaning OUTBOUND TX to field radios ) had mostly been planning the NB process for some time.
In that time, they either already had ERP licensed a few dB above what they were using, or went thru the coord. process to get the higher ERP if they could.
That is what we did.
As stated above a couple posts, often re-coordination can cause you to have to reduce ERP.
You sure would not want to do that.
We had licensed at least 3 dB more than we were using ahead of time.
So, when NB came, little to no coverage was lost by increasing "outbound" to the max we were licensed for at a couple places and just increasing by 3 dB at others.
I really believe that better coverage could be obtained by most systems if there were the money / time to put all radios in the "fleet" on the bench to really maximize the tuning.
But think how incredibly expensive that would be? ( over time, absolutely worth the money tho )
Just in the county I worked for last year there would be around 800 radios.
With transporting the radios to a central spot, bench test time, reprogram time, repairs, postage to and back for a certain number of radios, etc.
Not to mention what was already spent narrow banding the repeater systems, base stations, etc.
I don't see this getting done in more than a band-aid fashion for most of the rural country, the economics just don't support it.

[jfhtm350]

I have been playing more with the NFM setting on my frequencies. Some of them sound pretty good and some of them seem like they are using 14khz of bandwidth instead of 12.5. Hard to explain but it sounds like the spikes of the audio are getting clipped and seems like there is a 100 watt carrier and no modulation.

Furthermore I can change between wideband and nfm and the wideband will show another bar of signal than the nfm setting.