July 2012 Inbox
Thursday, July 12, 2012 | Comments
 Following are comments we’ve received from readers about recent online and print news and articles. If you’d like to comment on an article, email edit@RRMediaGroup.com.
 
 
Editor:
 
I have been following the saga where the T-band solution that we have had access to in many cities, which is providing us with good coverage either in repeater or radio-to-radio direct modes, has now been sold via the D block reallocation bill and for users to be moved to yet an undetermined frequency. While this is still a ways down the road, I was personally concerned when this came about. Many of our brethren in these difficult economic times cannot financially afford yet another switch to another band as result of the demise of T-band.
 
It almost seems where the D block allocation move is a guaranteed sale for some radio manufacturer when this happens for new equipment on a new band. T-band provides us with reliable, affordable, radio-to-radio, direct-ground-channel communications because the nature of the radio wave. From my perspective, a forced migration to a nonperforming spectrum such as 700/800 MHz would affect direct radio-to-radio communications in building or on fire ground with reduced range, as well as force us to once again buy new equipment. T-band works. Hopefully a workaround can be made using equipment that we have and not equipment that we will need to buy.
 
Charles Kirmuss
Director at Large
Rampart Search and Rescue
Commerce City, Colo.
 
Editor:
 
The FCC did Roselle Park a favor in dismissing its application considering the frequencies they applied for were channel 20 frequencies. Ocean County's system is routinely interfered with by DTV broadcast facilities on channel 20 and we are within the 50-mile radius of Philadelphia. This problem has existed for 10 years and has only gotten worse. Our only solution is to move to 700 MHz.  
 
Robert Bruno
Division Director, Wireless Technology
County of Ocean, N.J.
 

 
 
Editor:
 
This is great; a lot of the best frequencies not being used.
 
Scott Renz
Rays Electronics
Oak Harbor, Ohio
  
 

 
 
Editor:
 
In reference to Wayne County, Ind., requesting a waiver of the FCC rules to operate a VHF mobile repeater on 173.210 MHz because there is no spectrum available between 150 – 160 MHz for its use, I submit my idea. The use of VHF TV spectrum from 174 – 216 MHz would be applicable in this case if there is no VHF channel 7 in operation in the area. With the majority of TV stations migrating to the UHF spectrum for digital TV, thus opening VHF spectrum, this part of the band would be ideal for the type of operation that Wayne County proposes.
 
A few companies have produced wireless microphones that are used by the broadcast industry to allow multiple commentators to operate with receiving equipment that operates on the VHF TV channels between 174 and 216 MHz. These low-power transmitters have selectors to transmit on frequencies that are not in use in a particular area so that there is no interference to the receivers. This is just another idea for public-safety use of what may be an unused part of the spectrum in the future.
 
Gerald Marsh
 

 
In response to “Communications Key in Colorado Wildfire Response” from July 18:
 
Editor:
 
While not being in Colorado during the major fires this year, I understand that the fires threatened some of the critical communications infrastructure —repeaters, towers, etc. This might be another area to survey for improvements to make networks more robust. Of course this means there is probably not much left around those sites to burn, what about other sites in the area?
 
I am reminding our people that there are propane tanks located close to the towers and buildings and they need to handle those situations according to established procedures. My advisory was to let them know there is a hazard around the radio sites (BLEVY). We do not have large trees as much as burning grasses and scrub oak to deal with. We are working toward trimming the grasses short and clearing the scrub brush away from the towers and buildings. Just to make things interesting, there are also rattlesnakes to deal with.  
 
Glen Hollander
Salt Lake City
 
Editor:
 
During an all-hazards COML class, I had a heated discussion about this very topic with the people from the Denver area. Funny how it takes a real event to drive home that these billion-dollar communications systems are not the answer to all communications problems and interoperability.
 
Rodney Vorndam
COMT, COML, Type I, II & III Teams
 

 
 
Editor:
 
My concern is that this House committee is looking to provide for-profit commercial entities with federal spectrum that is used for essential public safety and public services, or worse, military frequencies used infrequently, but essential for the nation's security.
 
Rick Tannehill, P.E.
R.L. Tannehill, P.E. & Assoc.
Glendale, Ariz.
 

 
In response to “3 Advantages to Digital Radio from July 10
 
Editor:
 
I have to comment on the comments that shoot digital radio down. We find that the NXDN FDMA technology gives us from 35 to 45 percent more distance. Not physical, but with better forward error correction (FEC) and better audio quality in the fringe areas. We get 9600-baud data at 6.25-kilohertz bandwidth. We can get more, but we are happy. Just my 5 cents worth of experience.
 
Leon van der Linde
Global Communications
South Africa
 
Editor:
 
More efficient use of spectrum: I say digital radio barely fits in the 6.25-kilohertz channel plan, while ACSB and the deviate version called linear modulation fit easily in a 5-kilohertz channel plan, just a mere 20 percent more efficient, and it transports data at 16.2 kilobits per second (kbps).
 
The increased amount of information that can be passed down a single channel theory is more “digital is better” hype. The Dataradio solution was 64 kbps data in a 25-kilohertz channel. Now MOTOTRBO’s advertised best effort is 1.2 kbps without flow control per voice channel, and it hasn’t figured out how to “bond” two channels for a better solution. See above at 16.2 kbps, also. It seems that narrowbanding is just an effort to cut data bandwidth in half and in half again.
 
Improved clarity at low receiver levels approaching sensitivity is true, but you have traded absolutely unbelievable poor audio quality at any reasonable signal level for that — across your entire system footprint.
 
If your radio system is mission critical, it should be analog, so regardless of the signal level, you have the best chance of getting the message through — no matter where you are. Is there a place for digital radio? Yes, in the congested urban jungles of the world in non-mission essential communications, just like your cellphone, where dropped call is the performance norm.
 
Digital is simply not better. Ask all of the fringe digital TV viewers. The graphic provided is simply not true; it is exaggerated. At high signal levels, digital audio is not a tiny bit worse (it “looks” the same) than analog, it is hugely worse and difficult to understand. Listen to a DMR radio. It sounds like Robbie the robot with a sore throat. When digital radio mutes and cuts off operation, it is a straight-line drop from something to nothing with no hint it is getting ready to leave you with zero communications. Out here on the fringe, holding the radio up straight, adding a gain antenna and sometimes speaking softer and distinctly (remember FM limiting) will make the difference.
 
According to the graphic, the “area of improved performance” covers more than half of your service footprint. No, it is simply the last mile or so. The relationship between radius of operation and area covered is squared function; it is not linear. If it was half, the coverage result is a quarter.
 
James E. Sharp
Power System Engineering
Madison, Wis.
 
Editor:
 
Regarding the article on the digital modulation of radio spectrum, there is the teaser of "trade offs" using the digital side. I will agree that the spectrum is more efficiently used by digital, but the reduction of range and vocal clarity is, in my opinion, a great big drawback.  All of our information we have gathered about analog narrowbanding has shown about a 40 percent reduction in usable range of the radios. Digital modulation also shows a reduction of around 40 percent of range. Throw in largely multipath signals, and digital does not work well at all. Our users in the field are very dissatisfied with the reduction of range and the digital-sounding vocoders available now. Where are the " trade offs?” All I see is another article expounding the "virtues" of digital.
 
The only ones getting rich are the radio manufacturers. I find it disheartening that the radio manufacturers are "driving the bus" regarding the mandates to narrowband and go digital.
 
Just my two cents worth, but there are a lot of us out here.
 
Garrett R. Lang, AF7RF
Lead Electrician, Bridge Section
Multnomah County, Ore.
 

 
 
Editor:
 
Palidor Radio Communications Consultants is completely independent of all technology vendors/manufacturers, and commercial telecom services, so our interest is solely the interest of our clients, regardless of the type of technology that is used. System design is everything in controlling interference and providing reliable system performance, and the technology is secondary, as long as the technology is fully compliant with regulatory standards and meets minimum industry-accepted performance parameters for the intended design.
 
The VHF band in the United States and in Canada is a dog’s breakfast of interference problems, and this needs to be recognized by the system designers, and the coordinators. In today’s RF environment in the United States and Canada, any large system design in the VHF band should be avoided, because of the lack of a coherent band plan. But this has been a known problem for many years. This is not a new revelation.
 
The DMR Association is correct in placing the majority of the blame on system design. But the coordinators should not be blamed or criticized for trying to provide existing licensees as much protection as is practical. Blame the system designers, and to some extent, the technology vendors for ignoring the obvious pitfalls of knowingly supplying products and designing large digital or analog systems in the VHF frequency band, which has a well-known history of interference problems, regardless of the technology.
 
Fred Palidor
Palidor Radio Communications Consultants
Bellingham, Wash.
 
Editor:
 
While I am an avid supporter of Digital Mobile Radio (DMR), I think the response by the DMR Association to coordinator restrictions on VHF use of DMR is weak, ineffective, and never clearly identifies the real problem.
 
The article is incorrect in stating that most shared users on the VHF spectrum are business/industry (B/I) licensees. In fact, B/I users started getting off the VHF band in the 1980s with the advent of 800 MHz trunking. The major B/I users are on-site short-range users. There is virtually no mobile use of VHF by B/I users. Conversely, the majority of public-safety users are on VHF. (Editor’s Note: The article has been corrected.)
 
Let's deal with the problem as it really is. The main problem is with frequency pairing. To my knowledge, every reported interference case involves a VHF public-safety repeater user being interfered with by another public-safety repeater user. The user causing the interference is transmitting on the input side of the victim user’s repeater. The victim can be up to 100 miles away because the signal is transmitted directly between repeaters. I know of no known problem between UHF repeater users with paired frequency FCC authorizations.
 
Now we get to the subject that no one wants to discuss. In my limited communications experience, I have been taught that voice communications is stuff that I can understand. Anything else is non-voice, or "data" to the technically inclined. It seems I recall that non-voice communications is secondary to voice. So, unless the interfering user is operating on a channel authorized for trunking (FB8) or if the interfering user has a consent agreement from all co-channel users, then the interfering user must either fix the problem (to the victim’s satisfaction) or get off the channel. Private carrier paging operators and security system licensees operating on base/mobile Part 90 channels faced this issue many years ago. Once confirmed that voice trumps data (on voice channels), the problem was quickly resolved with a little assist from the FCC Enforcement Bureau.
 
The problem is compounded when the interfering user is transmitting near continuous data (AVL, text data, trunking polling, or all three) on a channel licensed only for voice communications. The coordinators are right. DMR should not be used on VHF frequencies. The problem is with manufacturers and dealers that have placed DMR systems on voice channels without the benefit of specifying data emission on their license application, obtaining FB8 authorizations, or obtaining clearance from co-channel users. The fact is (contrary to what some might say) that all DMR transmissions are non-voice. I've listened to DMR transmissions on an analog radio, and all I hear is a bunch of noise. I think some people call that non-voice. Some would call it data, but whatever you call it, it is not intelligible voice.
 
Having said that, the solution to the problem is not to authorize any VHF non-voice licensees on voice channels unless the channel is authorized only for local-area simplex use or for FB8 use and/or when written concurrence has been obtained from all co-channel licensees (and in particular if the co-channel licensee operating a repeater system). This rule would not apply to just DMR, but to NXDN and Project 25 (P25) as well. What's so complicated about that? The problem is with the stations that are causing problems to other users. In most cases, the user (and perhaps some dealers) is unaware of these facts. Then of course, there are those dealers and/or manufacturers that knowingly violated their customers’ trust by selling and installing systems that they knew would have problems. Dealing with those folks is a subject for another day. As far as DMR being a "polite" system, I have to wonder how many victims of this channel abuse would agree.
 
Burch Falkner
President
Falcon Direct
Birmingham, Ala.
 

  
Click here for the June 2012 Inbox.
Click here for the May 2012 Inbox.
Click here for the April 2012 Inbox.
 
 


 
 
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