Conventional Scanning
Remember the old days when you could enter in the local police and fire channels into your scanner, hit the
scan button and enjoy listening? While those days still exist in some areas, the new generation of scanners
are more complicated to program, even for the Plain-Jane conventional channels still used by many
agencies.
“Conventional Channels” mean voice channels that do not use some sort of trunking. Mostly you just need
to know the frequency in use and you can monitor the action. These days however even these need a bit
more knowledge or at least trial and error. Things such as CTCSS, DCS and the modulation Mode make
programming even conventional channels a challenge sometimes.
If you just want to listen to these basic analog channels then high-end models such as the PSR600 are not
for you. It’s like buying a Ferrari to drive two streets to pick up milk. It’s far too complicated and costly
when a simple low-cost model will work equally as well for basic channels. In much of the country
nowadays though you must have the Ferrari or otherwise you can’t listen any longer. There’s no such thing
as a simple (and low-cost) scanner that can monitor advanced radio systems.
FM vs. NFM vs. WFM
When you program in a conventional channel you need to know the proper Modulation Mode. If you are
listening to aircraft in the 108-136 or 225 thru 400 MHz. bands then AM is the proper mode. Beyond that
most communications are either regular FM or Narrow FM (NFM). Since the PSR600 does not include the
FM broadcast band it also does not include the WFM mode.
Over the last few years, and continuing until 2013, most conventional channels have been or will be
converted from what scanners usually call “FM” to a narrower format called Narrow FM. This allows
additional channels to be squeezed into the same amount of spectrum.
Until recently most VHF High Band (150 to 162 MHz) channels have been 15 KHz. apart, for example, the
next frequency used after 155.250 was 155.265, then 155.280. With the Narrowband initiative the channels
are now closer together, 7.5 KHz. apart. 155.250 is followed by 155.2575, then 155.265, then 155.2725 and
followed by 155.280. All users of the new channels in-between older channels must use NFM, and users of
the existing older channels must convert to NFM by 2013.
UHF is affected the same way, but some of the rules are different. Originally regular channels were 25
KHz. apart, for example, 460.275 was followed by 460.300 and then 460.325. The in-between channels
(called “Interstitials”) 12.5 KHz. apart from the main channels (460.275, 460.2875, 460.3000, 460.3125,
460.325) were restricted to low power use only. With the new rules these “12.5 KHz. Channels” or
Interstitials were allowed to use the same power levels as the original main channels (subject to certain
rules of course) and new 6.25 KHz. offset channels were allowed for use at low power.
In many areas the available pool of original VHF and UHF channels were used up and this method of
refarming the available spectrum allows more channels to be squeezed in. It is not without precedent, the
same thing has been done several times in the past, when VHF channels were changed to 15 KHz.
separation from 30, and 60 was the norm before that.
How will I know whether to use FM or NFM?
While the new channels are almost always going to be using the NFM mode, older channels could use
either, at least for now. Unless you know for sure you may have to try both methods and see which works
best. If you select FM now, your local agency might switch over any time, requiring you to adjust your
programming. If you chose the wrong mode you will still hear the communication, but at a reduced volume
or with distortion. If the volume is low, compared to other nearby stations, then you are likely programmed
to FM on a NFM channel. If the conversation sounds distorted or over-driven (like many CB operations)
then you may have a channel programmed in narrow mode still using regular FM.
