frequency modes

[itzdan]

I am new to scanning.

I get confused with all of the different modes. I find in the database a set of frequencies, in this case -

FREQUENCY DESCRIPTION
33.7000 ROCKLEDGE VOL FIRE CO 1
154.0700 ROCKLEDGE VOL FIRE CO 1
154.1300 ROCKLEDGE VOL FIRE CO 1
154.4450 ROCKLEDGE VOL FIRE CO 1
451.4500 FEDERAL LICENSING INC; ROHOWY MICHAEL
453.4375 ROCKLEDGE BOROUGH OF
458.4375 ROCKLEDGE BOROUGH OF


MY QUESTION - Which Rx mode do I set it to when programming my scanner? Is there a way I can tell just be looking at the frequency? I have to choose between FM, AM, MOT, EDACS, CT, and DC.

Thank you!

 

[rescue161]

FM is what you want for those frequencies.

But if they are using subaudible tones like CTCSS or DCS, then you can use CT or DC and it will keep out interference and let the audio of the agency come through.

 

[kc4jgc]

Hello Dan,

Easy question to answer. Almost all vhf/uhf in public safety below 800 MHz is FM. The aircraft bands are AM mode. The freqs you've listed are all FM.

MOT (Motorola) & EDACS (GE) are used when monitoring trunked systems. The transmissions themselves are FM; the difference is how the systems work. Both systems have data channels that handshakes the systems with their units. Both these systems are found primarily above 800 MHz; there are some US Government systems in the 400-420 MHz band that use trunking. DC and CT are new to me; can't advise on those.

Hope this helps,

Steve

 

[kb2vxa]

Hi Dan and all,

To be a bit technical, there is only one mode used in such communications, FM. There are however two types of intelligence, digital and analog, but both are transmitted as FM. That's the simple way of stating it, I won't confuse you with modem tones.

In the RR database unless marked otherwise it's analog and digital is marked according to the type used and of course there is trunking. Just program accordingly, those knowlegable can help you with programming talk groups which can be confusing to the newbie.

BTW, there's nothing like starting with the basics and figuring it out as you go along, you learn more than asking "dumb" questions and letting someone else think for you. In other words, ask when you get stumped and not before, it gives you a satisfied feeling of accomplishment.

 

[kc4jgc]

Appears Scottt & I were responding at the same time.

Not having your model scanner I wasn't sure what CT & DC were.

Continuous Tone Coded Squelch System (CTCSS, also known as the Motorola moniker "PL" for "Private Line") the transmitter sends a subaudible tone for the duration of the transmission. This opens the squelch on any reciever that is looking for that tone. In fact, If you plug a headset into your scanner, you will hear the PL tone quite easily. It sounds like a hum. There are 35 tones available from 67hz to 253hz.

In DCS systems, a transmitter sends a short digital burst to open the squelch on recievers looking for that same burst.

 

[John_M]

I looks to me that the first 5 frequencies that are listed are
most likely FM +/- 5Khz. The last 2 are NFM +/- 2.5Khz. To be sure of the first 5 you have to look in the FCC database for other frequencies used
in the same area. If a frequency pops up like 154.4475, then they are using NFM mode.