Coverage loss due to Narrow Banding

[TBerry1966]

I know the subject isn't "new", but I'm still struggling with loss of coverage due to narrow banding. What options do I have to regain the coverage loss? In some cases I'm experiencing about a 25% loss.

[Bill_G]

This topic has been discussed a few times. In my opinion, your loss of coverage is likely caused by your equipment not being aligned properly. Tell us about your system, what kind of equipment you're running, who does your maintenance work, and why you feel your coverage has diminished so much.

My offer stands - give me lat/long of your central site(s), freq, power, height, gain, etc. I'll create a plot that shows what your coverage should be and what you might theoretically lose after NB your system. If you have specific examples of areas that used to be reliably covered that are now radio dark, I can mark those on the plot. We'll throw some light on the matter, and help you figure it out.

[TBerry1966]

I appreciate the help Bill. Unfortunately, I can't give specifics on coverage areas. I am the Radio Tech. for Corrections (the Prison System). I have seen between 10-25% coverage at our facillities since we Narrow Banded. Each facillity has it's own issues with coverage. I run mostly MTR2000's but there are a couple of 3000's in play. We're experimenting with Digital in a couple of situations, and coverage is better there.
Repater, and Antenna locations are based on each facillities coverage needs. As you can imagine, I deal with a lot of concrete and steel.

[TBerry1966]

I'm still having difficulty with this issue. ANY help, input, or opinion is appreciated.
So for the only thing that seems to help is cranking up the TX power from my repeater. That gets my portables to RX, but they still can't TX back to the repeater with any reliability.

[N4DES]

Before someone gets hurt and there is a lawsuit based on a known radio deficiency, your management needs to get a professional in the facility to correctly design the system taking into account the narrowbanding and the building design and then have it implemented.

Yes it will cost some bucks, but I'm sure a lot less than a long term workers comp claim or worst yet a lawsuit brought on by a hurt employee.

[Bill_G]

Ah. Indoor coverage issues. A plot would be pointless.

If you had the coverage before, and nothing else has changed except programming the radios for NB service, you should have the same coverage now. The footprint should not have changed. Especially indoors. If you are experiencing this much difference with such a minor change in deviation, your systems have always been on the brink of failure.

First thing is to PM every radio, and make sure they are working as hard as they are supposed to. Go through every portable. Make sure they are on freq, got good power, got good rx sense, got good batteries, good mics, and good antennas. Set a baseline for performance, and replace anything that doesn't meet that spec.

Check your repeater desense. Maybe there has been a problem for a while with the duplexer, line, and/or antenna robbing inbound signal. Have the lines swept with an Anritsu or similar TDR to verify there are no failures.

You may have way too much gain on the repeater antenna. It could be shooting towards the horizon, and not landing in your complex. Get a lower gain antenna with more natural downtilt.

Get a voter. Portable coverage is notoriously bad. Voters and receivers help the inbound path immensely, but d nothing for the outbound.

You may have to invest in a DAS even if it's a simple one that runs across the roof of the main house. At the very least, drop a line into the building to a second antenna in the basement level.

I hope these ideas help.

[kb4mdz]

Another vote for what BillG says.

Hindsight being 20/20, all these PM things should have been done before NB.

Esp. frequency error; if a portable is rated at 2 PPM frequency error, at 460 MHz that's a freq error allowed of over 900 Hz. I've seen plenty of radios work 'OK' at this, and even more than 1KHz freq. error. in 25 Khz mode. When you narrowband the radio the that 'allowable slop' gets reduced, too.

If my math were still up to snuff, I could work up some diagrams as to why,

Many radio shops have done "Wonderful things' when taking over a radio system from another shade-tree radio tech, by just PMing it properly; make sure freq. error is tightly controlled (good modern equipment can easily meet +/- 200 Hz freq. error without breaking a sweat), re-align wireline & repeater levels, modulation is good, antenna system is good, etc.

Good luck.

[TBerry1966]

Thanks Bill

I've reasearched the subject well, and even the FCC informs that NB will cause "some" coverage loss. Around 4% seems to be the most commonly noted loss. Some testing even states losses up to 26%.

When I did our NB, we had 36 facillities averaging 120 portables, 3 mobiles, and 2 repeaters each.That's just our VHF/UHF stuff, we also have +/- 2500 800Mhz. I personaly touched +/- 90% of the equipment that was NB'd. I am the ONLY Radio Tech for our department. My supervisor and I tackle EVERY radio issue, in some way, ourselves.
All of our equipment is running as efficiently as possible. We are 100% Motorola. Each antenna was thouroughly spec'd for it's facillity.
LONG story short, before NB we had 98% reliable coverage at every facillity. Now we have +/- 88% on average.

Again this is State Gov't. I can't (although I wish I could) just wave a Magic Wand and have unlimited funds, equipment, and man power.
Sorry to sound curt, I'm just very frustrated.

[Bill_G]

You don't have to apologize TBerry. When you said prison, I kinda figured you were the lonesome tech for a bazillion users, and what I was telling you to do would be logistically impossible. If you are confident that your equipment is working at it's peak, that there is nothing left to tweak, and you suffered that much coverage loss, then your system was on the edge of performance failure already. You lost your fade margin, and now you're discovering all the areas that were poorly served in the past.

Since you know where these areas are, that's where you have to put your DAS antennas. You and your manager need to push for the agency to hire a consultant who will write up the bid specs, get it on the street, and award a DAS project to a contractor. Get it in the budget. You've got reality and research to back you up. Nothing you can do except push it upstairs and hope they make it rain in the next budget cycle.

[TBerry1966]

I've been pushing for a DAS / BDA in similar situations, since before NB was even an issue, with NO luck at all. Unfortunately, as with most other parts of State (or ANY) Goverment, this department is REactive instead of PROactive. I'm afraid something tragic will have to happen before something gets done, and that's what I'm trying to keep from happening in the first place.

[Bill_G]

Not much you can do except what we've already discussed - go back through everything. Test it and verify it one more time. This would be the perfect opportunity for an outside qualified contractor to come in. They can throw more labor at it than you can, get it done faster, and one of the deliverables will be a report showing the current state of the systems per property. Another contractor could be hired to do site surveys that produce coverage maps of the buildings either as color temp, or basic pass/fail based on a criteria you set. With just the two of you doing this work, and all your other duties, you can't fully address all the issues.

[TBerry1966]

I agree Bill. I'm not going to hold my breath though, as I've stated before this is a REactive enviroment. I've done all I can with what little I'm given. All I can do now is voice my recomendation/opinion and hope for the best.I do appreciate your support and especially all of your help.

[gtriever]

Bill's given some good advice here, as he always does. The only thing I can say is document, document, document and keep a paper trail including emails to your higher-ups.

[Bill_G]

Sorry for necro-threading, but we had an odd experience with a well known company here recently (not the famous five letter multinational that begins with the letter I) that fits the discussion of this thread.

They've been using a competitor for quite a while to maintain their standard UHF repeater system - Single repeater with rooftop antenna to cover the plant and the grounds. Coverage was never perfect. They went through the narrowbanding process replacing all radios - it got worse. They upgraded to NXDN digital service. No change. Eventually called us. Our tech discovered there was no duplexer on the system. No window filters. No cavities of any kind. Nothing. Just power splitters for the transmit lines, and a multicoupler for the receiver lines. Two strands of half inch heliax meander through the plant with two primary antennas on the roof ten feet apart. The indoor drops vary from a few feet apart to several yards apart. Our tech recommended a duplexer. The customer response was an emphatic NO. Their engineers determined this design should work - no duplexers needed - fix it. I told him to walk away.

Is there some new magic out there we are not aware of? Are there DAS designs that work without incorporating filters? Are there repeaters that function without sufficient antenna separation? We are trying to figure out why these engineers insist on this configuration.

[kb4mdz]

Bill -

So the customer's engineers designed this system? But it doesn't work.

Good call to walk away.

Arrogance & hubris are not confined to politicians, manager wanna-be's & such. Engineers are also subject to (their own special brand) of it.

[nukedude]

My experience was very similar to the ones right above. My previous employer had engineers that said they would lose 50% coverage, have to buy a bunch of repeaters and go digital on hardware. Since several of us had rotated to this company right out of the military, we had been digital and narrow-band for 10 years already and dealt with this on the NTIA side already.

I had two sites that had just bought "new" radios, one site bought Motorola XTS2500's and another site bought XPR6550's. They initially called me since I managed the radio network for another company that interacted with them often. I have military and emergency management experience with setting up radio networks in odd places (after hurricane Katrina, BP oil spill and such). Their first question was why they could not talk between sites when they used to on their old radios.

Knowing these people, I knew they had just replaced analog HT1250's at both sites. I then had to explain to them that they did not have to "go digital" in order to narrow-band, and that the local radio shop had pushed this to get a sale. Then I explained FDMA and TDMA versions of Motorola digital. Then came the narrow-band coverage. They had been on the edge of losing signal between buildings in analog mode on their HT1250's. Each site had engineers that swore they knew what would work. So each site bought different types of Motorola digital radios, and then wondered why they didn't work together or have the range they had before.

My recommendation was to set up an analog channel to use between buildings and to actually use some of the repeaters they had bought a few years earlier. I then stayed out of the messy aftermath. Neither site could return their newly bought products, so they added an analog channel to their radios. The repeaters were still in storage 6 months later. I went to another company.

[Bill_G]

(looking for the dope slap smilie ...)

Way too much fun. This is how a $19K PTP link gets on a rooftop strapped to an old wooden pallet barely peeking over a parapet with CAT5 running across the roof poking out a HVAC vent, drops five floors, squirrels across the ceiling to the NOC, and enjoys so many frame errors they're lucky to break a couple megabits of throughput.

[desperado]

One of the things I ran into with narrowbanding was antenna gain issues, oddly enough the antenna having too much gain and the radiation point being too low. I had a customer that had a high gain Station Master antenna on a sled mount on the roof of a building that when we narrowbanded them the radio coverage died. It was bad to the point that line of sight to the building was even effected because the low radiation point of the antenna was sending the signal over the heads of the users. We pulled the station master and put up a unity gain antenna in it's place that was just as tall but the 18 foot stick was replaced with 14 foot of pipe and a 4 foot antenna. Worked as well as it had prior to narrowbanding at that point. Yes the antenna was a bit old but both sweeps and field strength measuremnets off the antenna were as expected. I honestly can't say WHY it fixed it, only that it did.

[Bill_G]

Sounds like a system riding the edge of failure for a long time that needed the theoretical 3db NB loss to function. OTOH, it wouldn't be the first time I've seen a high gain antenna in the wrong application with low or no close in coverage to the site, but great coverage on the horizon where the customer doesn't need it. It's the classic "put a 10db colinear on the roof of the tallest building on campus" and then wonder why facilities has no coverage in the service tunnels or lower level parking.