2017 ultra narrow banding, really?

[E5911]

What are your comments/opinions about the likleyhood of the 6.25 narrowbanding for 2017 affecting frequencies above 150mhz and below 700. I am aware 7-800 has a deadline in the hopper. Is it likely this is going to happen, or not so much.? Lots affected by going that route.

Trying to get a handle on it.

[mmckenna]

Unlikely it's going to happen. 6.25KHz requires digital, and that would require replacing all radios and all repeaters, pagers, receivers, etc. The one thing that made the 12.5KHz rebanding halfway bearable was that all new radios in the last decade or so have been narrow band compatible. Considering that the rest had to be replaced with new equipment, no one is going to want to have to replace all their equipment again. The recent narrow banding was in the works for a long time. 5 years just isn't reasonable.

Will it happen, probably, but not in 2017. 2027, 2037, who knows....

[wd8chl]

No, there will absolutely not be a 6.25 Khz mandate for VHF/UHF that soon. As tough as things have been for rebanding and narrowbanding, neither of which is even close to schedule, well, it's just too hard to do. First, it would take longer than that just to put together what the final landscape would look like, and what rules would need to be implemented. No, in fact, with the public safety broadband network in the works, I think there won't really even be a need to ever do 6.25 KHz. At least not in the next 25-30 years or more.

[cavmedic]

There are still counties that have not completed this narowband update.... They may be done just in time for that one though..

[SteveC0625]

It took a full 20 years to implement the 12.5 mandate. For all the reasons already mentioned and more, it'll be at least another 20 until the next one. The only thing that might change that is a HUGE infusion of grant money Even that might not work. There would be too many agencies and businesses saying, "We just spent tons of our money to implement your unfunded 12.5 mandate. We're not doing it again for a long, long time!"

[petnrdx]

I agree, there is no way that another "narrow banding" step could be done in anything less than maybe 20-25 years.
Millions of radios, hundreds of millions of public money would have to be spent.Likely WAY more.
And like some above have stated, there may not be the "need".
And, again, there are still many that have not completed the 2.5 NB.
More likely the next "narrow banding" will be to a new modulation scheme, maybe even one that doesn't exist or is in the development stage.
The next 10 years will be particularly interesting.
I think this next 10 will determine what is "chosen" and is then mandated 10 or 15 years further.

[RKG]

There is another factor to take into consideration, which tilts against a 6.25 channel spacing (at least so long as analog radio is permitted and employed).

The rule of thumb for how much spectrum is actually occupied by an FM channel encoding analog voice is 2 times max. deviation plus six.

Thus, wideband channels occupy about 16 kHz of bandwidth (2 x 5 = 10; 10 + 6 = 16). This fits easily within a 25 kHz channel spacing, with some room at either side for slop.

Narrowband channesl occupy about 11 kHz of bandwidth (2 x 2.5 = 5; 5 + 6 = 11). This also fits within the assumed channel spacing (12.5 kHz), though a bit less comfortably.

Now run the numbers for 6.25 kHz channel spacing, using a max. deviation of 1.25 kHz: 2 x 1.25 = 2.5; 2.5 + 6 = 8.5. Ooops; a nominal 6.25 kHz actually occupies about 8.5 kHz of bandwidth, or about 136% of what it is supposed to. Put up some 6.25 kHz analog channels and you're going to get some interesting adjacent channel interference problems.

Which is why when people begin speaking about 6.25 channels, they are implicitly talking about digital voice modulation. It is also why radio manufacturers have been pushing the FCC to accept "6.25 equivalent" channelization (i.e., two simultaneous voice paths on one 12.5 kHz channel, using digital voice modulation and time division multiplexing on the single 12.5 kHz channel), so far with no success.

There are other issues. I mentioned "slop" above, and here is one component of unavoidable "slop:" put a dozen handheld transmitters on a good service monitor and you'll find that not one of them is actually transmitting exactly on its assigned center frequency. Tight frequency control is difficult and expensive to maintain, and usually requires conditions you aren't going to find with a hand carried, battery powered unit in the field. Indeed, tolerance of frequency drift was one of the reasons for going to FM in the Land Mobile field in the first place; unlike AM (including SSB) transceivers, an FM product detector will yield human speech with reasonable tonal fidelity even if the receiver and transmitter are on slightly different center frequencies.

The FCC has long dictated how much "slop" is permissible. For portable radios, the value in most cases is 2.5 ppm. At 460 mHz, this means your radio can permissibly vary from center frequency by plus or minus 1150 Hz (or 1.15 kHz). Hence the need for a guard band around channel occupancy but within channel spacing. 12.5 kHz channels have a marginal guard band; 6.25 kHz channels have a negative one.

So for a lot of us, 6.25 kHz channels are pie in the sky until the Government decides to outlaw analog voice altogether.

[Mike_G_D]

RKG, all good points; I'll only add that as the deviation of analog FM is reduced the benefits of amplitude dominated noise immunity inherent to FM goes down. At +/-2.5KHz deviation we are pretty much at the limits of getting any inherent benefit from FM noise immunity. That plus, as you inferred, the BW limitations using analog audio frequency modulation when going this low in deviation and the limitations of discriminators and local oscillator (and PLL) stability mean that the usefulness of analog FM using less than 2.5KHz deviation is pretty much nill. Even if we add powerful analog post processing using DSP engines to compensate for the hardware limitations then we contend with the idea that we are now adding lots of digital heavy lifting to compensate for weakly defined analog audio and might as well be putting all that digital processing to actual digital signals right from the start - so, pretty much, going lower than 2.5KHz deviation means going to digital modes.

Currently, I am aware of only one widely used (relatively speaking) true full FDMA only 6.25KHz BW LMR system: NXDN (and may be the dPMR open standard it was based on...not sure here). That is true RF channel 6.25KHz BW per voice channel and not "6.25KH equivalent" as in TDMA systems like DMR/MotoTrbo. As I understand it, that is why the American railroad companies have pretty much adopted NXDN as their new standard for future use in hopes of being compliant with far future narrowbanding requirements. Plus, in the US civilian VHF LMR band where railroad radio is mostly centered in, the actual channel spacing is less than the Carson's Rule BW as defined by RKG. Up till recently it has been 15KHz and is now 7.5KHz. The new railroad US channels are now 7.5KHz splits and using some form of true FDMA 6.25KHz compliant modulation will, theoretically at least, help them get the most out of those extra channels.

-Mike

[mmckenna]

Correct. We will never see analog FM below 2.5KHz deviation.

I've used 6.25 digital NXDN and it works very well, and as you said, is TRUE 6.25, not a equivalent that only applies when working through a repeater, like Trbo is. Looking at all the options, I hope NXDN or some variation of it is the more popular of the two in the US. DMR is already ruling in Europe by a wide margin.

I think this horse has been well beaten and the OP's question has been answered.

[petnrdx]

Yep, it is gonna' be interesting.

[Mike_G_D]

Originally Posted by mmckenna

Looking at all the options, I hope NXDN or some variation of it is the more popular of the two in the US.

Yeah, I don't think that will happen. DMR/MotoTrbo is very popular and now widely used and, for many, TDMA systems really offer the best bang for the buck. And the big M is backing it so that is a lot of inertia. To be honest, I think there is room for both approaches and each have advantages and disadvantages for different situations. I rather think that MotoTrbo will be eventually made capable of operating within 6.25KHz RF bandwidth, at least for direct off network simplex use. In that sense, it will turn into true FDMA 6.25KHz BW when in direct simplex mode just like NXDN. What they do with the repeater format will probably be to stay in 12.5KHz mode with two slot (or more?) TDMA channels for the foreseeable future until the FCC really demands true 6.25KHz BW usage (if they ever do).

The nice thing about TDMA systems is that they give some leeway to operators of already in place RF systems in that much of the RF plumbing can stay the same while still yielding a doubling of channel capacity. Capacity becomes more of a digital IT type concern and stays out of the touchy and expensive RF realm.

For customers who have no infrastructure already in place, there is a choice - they can choose FDMA systems or TDMA systems. In very crowded RF dense areas, it might make sense to go with FDMA 6.25KHz BW systems especially if there are already other such systems in place nearby. And, of course, for users desiring the advanced signalling and selective calling features of digital modes plus the extra channel capacity but does not need or want to use on-site infrastructure then NXDN is the most logical current choice - at least until MotoTrbo (or DMR in general) gets 6.25KHz simplex voice channel capability.

-Mike

[mmckenna]

We trialed a MotoTrbo system and we were happy with it. It certainly worked well and sounded good.
There were three issues we ran across that drove us to Kenwood,
We use the NPSPAC 800MHz frequencies for our system, and Motorola specifically blocks the NPSPAC frequencies from the MotoTrbo radios. We asked them why, and their answer was that if we were using NPSPAC, we were public safety, and therefore must use P25. We had previously priced out a P25 trunked system and all the subscriber units and we were coming in close to $2 million. Even though this frequency limitation is a software thing, Motorola refused to budge. One of our other sites was using MotoTrbo radios on these frequencies, but only in SmartNet mode, so Motorola was willing to change it for the right reasons. We even looked at staying on SmartNet and purchasing the MotoTrbo radios and using them in that mode only, but we couldn't get any guarantee that Motorola wouldn't change their mind in the future and stop allowing the newer radios to support that mode in those frequencies, and anyway, SmartNet is on it's way out, so no point investing money there. We even looked at licensing new frequencies, but the cost associated with doing all the coverage plots for a new band, all new infrastructure got to be way too expensive. We even looked at T-band (before the plan to dump that).
The other issue we had was that we had a 5 channel system and it was plenty of capacity. Replacing that with 2 MotoTrbo repeaters, basically would have given us the same capacity, however if one repeater failed, we'd lose 50% of our capacity.
Kenwood, on the other hand, met us with open arms and worked hard for our business. The 800MHz NexEdge radios allow the full spectrum of the 800MHz band without any issues, and came out to be slightly cheaper. Kenwood has worked pretty hard since we chose them to keep us happy, which is more than we could say for Motorola when we were still running SmartNet.
The real sticker was that when I was narrow banding our fire department, we ordered an MTR2000. The one they shipped was a low split model, instead of the high split model we ordered. It took me 2 weeks for Motorola to even acknowledge there was an issue, and another 2 months before they delivered the correct unit. Even with all the escalation, Moto refused to speed things up. I had to find a replacement unit form a neighboring agency to get our system narrow banded in time to match the surrounding agencies. It was a really disappointing situation that could have been handled much better. Not an equipment failure, but a customer service failure. Unfortunately, that has been our experience with Motorola recently. Mostly excellent radios, but disappointing customer service. Didn't make me feel all warm and fuzzy about purchasing a big system from them.

When we were faced with basically similar solutions, what really won out in the end was the attention the manufacturer was willing to give us. I love Motorola gear and own some personally, and we still use quite a bit of it at work, but they do have a lot to re-learn about how to treat their customers. Kenwood has seen this and been willing to step in and pick up the disenfranchised ex-Motorola customers.

Not wanting to sound anti-Moto, I'm not. Just pointing out what drove us to choose NexEdge over MotoTrbo. If Motorola would improve their customer service skills back to previous levels, they'd really see a big boost in sales, at least that's my opinion. I've talked to many others that feel the same way. It's really a shame, Motorola really makes great products, at least on the higher end of their spectrum. But then again, so does Kenwood.
I think Motorola is in for a good challenge over the next few years. Likely they'll do just fine, but I hope they can improve the customers experience.