Saturday, June 6, 2009

Are you narrow or wide?

Recently our local repeater coordinator began asking your emission designator on the application form. A break-down of emission designators can be found in section 2.201 of the telecommunications part of the code of federal regulations.

20K0F3E - FM Voice 20kHz bandwidth - Wide 
16K0F3E - FM Voice 16kHz bandwidth - Narrow
11K2F3E - FM Voice 11.2kHz bandwidth
8K10F1E - P25, phase 1, 12.5kHz Bandwidth
5K76G1E - P25, phase 2, 6.25kHz Bandwidth
6K00F7W - D-Star, 6kHz bandwidth

The confusion I often see lies whether a system is narrow or wide. 20 KHz bandwidth or 16 KHz. To determine this we must look at Carson's bandwidth rule.

As you can see in the analog world, your bandwidth will be determined by transmitter deviation. If you have 5 KHz deviation (now a days considered wide band I guess) you will occupy 20kHz of bandwidth. If your deviation is in the 2-3 KHz area you will occupy 16kHz bandwidth now referred to as narrow FM.

Now a days wide / narrow transmitter deviation is usually a software selectable option. The quote/unquote standard for ham radio has been 5KHz max deviation/20kHz bandwidth.

If you can't determine by software/programming configuration you'll likely need access to a deviation meter or service monitor to determine your deviation.

+/-2.5kHz maximum deviation is also a standard for 800 MHz and above and has been since the mid 90's. This is why you typically see 12.5kHz channel spacing up there. Actually I have never seen any Wide analog FM above 800 MHz except on remote broadcast studio-transmitter links. 

So if nothing else use the mid 1990's as a date of determination. If we are talking VHF/UHF commercial equipment manufactured 1997 or more recently you can probably assume it's "narrow FM"/Max 3 KHz deviation - yielding 16kHz bandwidth. Another clue is if it was in commercial service using a 12.5 kHz step/channel spacing scheme, it is likely narrow FM.

Here is the history: 
A process of "refarming" the informal name of a notice and comment rule-making proceeding (PR Docket No. 92-235) opened in 1992 to develop an overall strategy for using the spectrum in the private land mobile radio (PLMR) allocations more efficiently to meet future communications requirements. The FCC created mandates for the two-way radio equipment manufacturers. In 1997, all new two-way radio models had to be capable of operation on the "new 12.5 kHz narrowband" channels. This is often called "dual-mode" equipment since the radio can accommodate both narrow- and wide-band channels. The idea was to begin to move gently toward narrowband channel operation over time. At that time, the FCC did not create any mandates to remove older wideband radio units from service or require you to use a new narrowband channel.
The Part 90 LMR narrowbanding mandate was released 12-23-2004 by the FCC for all Part 90 business, educational, industrial, public safety, and local and state government two way radio system licensees currently operating legacy "wideband" (25 KHz) voice or data/SCADA radio systems in the 150-174 MHz (VHF) and 421-512 MHz (UHF) bands. The executive summary of the FCC order  establishes January 1, 2013 deadline for migration to 12.5 KHz technology.

(Note many ham HT's are capable of WFM / Wide FM receive, intended for reception of FM radio/ Analog TV audio. Don't confuse this with the two way standard... Broadcast Wide FM is 150 KHz of bandwith.)

True narrowbanding a receiver is what is hard.  I am talking narrowing the receiver IF bandwidth.

Just be aware that converting a 1950's era repeater to D-Star or P-25 that might have a 60 Khz I.F. would be vulnerable to adjacent channel interference. A good overview of the theory can be found in a reprinted article from Ham Radio Magazine 1985, by WD5IBS.

No comments: