If you're not upgrading to digital, don't downgrade to Narrowband FM!
Advanced Repeater Systems

No HAM Narrowband FM

There is a FCC mandate that all Part 90 Land Mobile Radio (LMR) systems operating in VHF high-band and UHF convert from Wideband FM (+/- 5 kHz) to Narrowband FM (+/- 2.5 kHz) or a digital technology to double the number of channels on January 1, 2013. This mandate excludes VHF Low-band, Paging frequencies, VHF Marine, the 800 MHz band and the Amateur radio bands.

However, there is a push by Amateur Radio Repeater Coordinating Councils, such as the Florida Repeater Council and others, to require future coordinations and eventually ALL Amateur FM repeaters to convert to Narrowband.

You say- So What? It's more bandwidth efficient and it worked in the 60's when we went from 15 to 5 KHz, so why won't it work now?

Well read on...

First, lets deal with the old +/- 15 KHz wideband systems. This was before the advent of highly selective and inexpensive crystal, Intermediate Frequency (IF), bandpass filters. IF filters were implemented with large Inductor and Capacitor (LC) Filters and by their nature, it was difficult to achieve a highly selective narrow bandpass response. Frequency stability was poor which was also a factor for the 50 KHz channel spacing. In the early days of two-way radio there were few systems and they were expensive to own and maintain.

As time moved on technology and radio equipment improved and more radio systems appeared. In response, the FCC mandated that all FM LMR systems reduce deviation from 15 to 5 KHz to double the number of channels. The FCC allowed modification of wideband radio equipment to the new 5 KHz narrowband standard by installing vendor provided IF filters, parts and instructions for increasing receiver audio gain and decreasing transmitter modulation.

This worked well because the new 5 KHz narrowband still had a substantial 1.667 modulation index.

            (Modulation Index = Max. Deviation/Max. Mod. Frequency)

However, this isn't the case for the new round of Narrowbanding which has a modulation index of just 0.83!

This 6 dB reduction in deviation results in a 6 dB decrease in signal to noise and a loss of up to 30% of coverage to and from your repeater. Of course Narrowband FM works fine in strong signal, full quieting areas, but when you get in the fringe, Narrowband FM degrades rapidly. It takes at least a 3 dB (or more likely 6 dB) increase in transmitter power to make up the difference!

In real world terms, if it takes 1 watt to hit your repeater, switching to Narrowband, may require at least 2 and up to 4 or more watts for the same Signal Quality! Imagine how hot your handheld will be, shortened battery life and increased RF radiating into your head, among other things...

Don't believe me? Read the FCC Narrowbanding FAQ:

http://transition.fcc.gov/pshs/public-safety-spectrum/narrowbanding-faq.html#question_2_3

Will I lose coverage area when I Narrowband?

It has been estimated that Narrowband compliance can result in a 3 dB loss in signal strength. However, this rule of thumb is based upon a "plain vanilla" Narrowbanding scenario where a 25 kHz analog system converts to a 12.5 kHz analog system. Consult with a manufacturer and/or consulting engineer for a better estimate of how Narrowbanding will affect your particular system.

If the FCC says 3 dB, would you consider this the final word? When has the government ever been right about an estimate?  In reality- real world tests by ARS and many others reveal the actual number is closer to 6 dB (4 times more power) to make up for the coverage loss of going to Narrowband FM!

Motorola, the undisputed leader in two-way radio innovation, quickly recognized the shortcoming of Narrowband FM and developed a Narrowband companding system called X-PAND.

From a Motorola Brochure:

  • X-PAND keeps a radio that is built to last 25 years from being obsolete in seven because you can switch to 12.5 kHz and preserve audio quality
  • X-PAND technology actually compresses your voice at transmission
  • At the receiving end it expands it while simultaneously reducing extraneous noise
  • X-PAND technology at 12.5 kHz can actually out perform 25 kHz sound quality...

If Motorola had to offer a solution for Narrowbanding to get back the 25 kHz sound quality, what does that say about Narrowband?

Knowing that Narrowband may be a reality, and the fact that my Icom D-Star radios have Narrowband FM, I added a Narrowband FM mode to one of my 440 MHz D-Star repeaters. (Yes, D-Star receivers have the same +/- 2.5 kHz equivalent Narrowband bandwidth) Using a DB-420 antenna duplexed and connected to a receiver multicoupler, I also have an analog wideband FM repeater running the same transmitter power and antennas at the same site.

We found that the Narrowband repeater, even at modest range, had almost constant mobile flutter, and was consistently scratchy and difficult to understand. Switching to D-Star the copy was perfect and continued for many miles whereas the Narrowband analog became virtually unintelligible especially while the vehicle was moving.

The analog wideband repeater provided significantly better audio quality with range similar to the D-Star. In the fringe, the wideband repeater with a 5 watt input signal operated as well or better than the Narrowband with a 25 watt input signal (a 7 dB increase)! What an eye opener.

These tests were done with various FM Narrowband Icom D-Star mobile and handheld radios over a period of several months.  We simply verified what the numerous engineering analysis and studies said that FM Narrowband results in up to 30% less coverage and requires up to 4 times the power to achieve similar wideband FM coverage. Not practical for the average Amateur repeater operator.

It became clear what this Narrowband mandate was all about; which wasn't about doubling the number of channels for analog FM systems, but rather for conversion to digital.

Don't confuse analog FM with Digital Modes such as D-Star GMSK, P-25 C4FM, IDAS and NXDN 4FSK and others, they are not the same. Typical FM voice communications is dynamic averaging just 30% of maximum modulation index (or an effective modulation index of just 0.25!) whereas digital waveforms are always at 100%.

Further, digital systems use all or a combination of: high-performance Phase Locked Loops (PLL); Digital Signal Processing (DSP); and Forward Error Correction (FEC) to lock on and process noisy and faded digital signals down to the noise floor (which causes the waterfall, all or nothing effect). In fact P-25 with its equivalent 12.5 KHz bandwidth, has a 8.9 dB improved coverage footprint over Narrowband FM!

        See: http://acdtelecom.com/Narrowbanding.pdf

Even with these digital benefits, in many cases, digital still does not work as well as good old wideband FM. Numerous public safety agencies that made the switch to digital have come back to analog, especially those using M/A Com equipment. P-25 (which is considerably better than M/A Com) suffers from microphone overload, among other issues. Many users (especially Public Safety) dislike the robotic sound, the audio latency and poor fade recovery of some digital systems.

Narrowbanding has another serious issue with Amateur operations, this time with the FCC Rules and Regulations, 97.313(a):

    97.313 Transmitter power standards.-

(a) An amateur station must use the minimum transmitter power necessary to carry out the desired communications.

Requiring Amateurs to Narrowband their Repeaters would cause Amateurs to increase their power to at least twice or more, to carry out the same communications, which is contrary to 97.313(a)! Therefore, requiring Amateur Repeaters to operate in Narrowband FM may actually force Amateurs to violate the Rules!

Further, Amateurs likely don't need to increase the number of repeater channels when hardly anyone is using the repeaters that are on the air now! I frequently travel the country with my dualband mobile and handheld radios scanning both the 2m and 440 MHz ham bands. If it weren't for the cable television leakage, I'd almost have nothing to listen to, even in some of the country's largest cities.

There are much better solutions that would allow additional Amateur repeaters such as closer spacing, issuing new coordinations on pairs with little use and perhaps something really creative (for Hams) such as repeaters that use multiple channels, similar to trunking, but these solutions would likely be too complicated and controversial for most hams.

With few exceptions, there are almost always pairs available if one searches. Frequency Coordinator's Databases often contain errors and paper repeaters. Repeater owners lose interest and take their Repeater down; Repeaters break and go away, never to return; Repeater Sites are lost; Owners move; Owners die; Repeaters don't exist, etc., etc.

Forcing Amateurs to convert their repeaters to Narrowband would likely deal them a death blow! Who is going to operate on a repeater that requires high power and is constantly noisy and difficult to understand?

To make matters worse, Narrowbanding is often pushed by non-engineering Frequency Coordinators who haven't a clue about the impact; other than the commercial LMR world is doing it; so why can't Hams? Afterall, their job is to coordinate repeaters and to do that, they need channels, lots of channels. They aren't worried about the quality of service and that repeaters will have 30% less range and that Hams will be running considerably higher power which will increase co-channel and adjacent channel interference.  And I can promise you that they have never considered these unintended consequences.

The FCC decision on Narrowbanding came about in the mid 1990's before the Cellphone and Internet explosion and was largely based on the false expectation that operations on the VHF and UHF bands would continue swell which, as we all know, never happened. Wireless technologies have all but killed LMR; as the VHF and UHF spectrum is mostly vacant in all but the most populated urban areas. It would have made sense for the government to mandate Narrowbanding only in these areas (which equates to less than 4% of the United States). But no; the FCC forced Narrowbanding on the whole Country.

For example here in Florida, there are many rural Florida Counties where there is virtually no UHF activity and the FCC mandate is forcing low-budget Sheriff's departments to replace their perfectly good wideband equipment with brand new narrowband compliant radios. Not only do they have to bear the cost of replacing equipment; they have to pay for engineering analysis and the installation new sites, towers and equipment required to make up the coverage lost by Narrowbanding.

And the real shame is- there isn't anyone on the adjacent channels for a hundred miles!

Remember what every Communications Engineer knows: BANDWIDTH IS YOUR FRIEND!

Sure 5 kHz wideband FM may have less spectrum efficiency than the digital alternatives but it works, it is very reliable, and has excellent range and clarity! But if you are going to communicate with FM with any coverage and range expectations, reducing deviation reduces your range, intelligibility and will at the very least require doubling (or more) your transmitter power, so says communications theory, the FCC and anyone who has tried it.

If you're not upgrading to digital, don't downgrade to Narrowband FM! Keep your 5 kHz repeaters the way they are!

Save Amateur FM Repeaters by Fighting Against Any and All Attempts to Force Amateurs to Narrowband FM!

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