Spokane/Stevens county

cs0139

Member
Premium Subscriber
Joined
Oct 13, 2010
Messages
30
Location
Eastern Washington
I’ve been listening to fire traffic including DNR on my TRX 1. I’ve noticed there is aircraft fire traffic that comes through on 154.747500. This shows up as Stevens County SO channel 3. My screen also shows CTCSS 203.5 which I don’t know what that is. Today the plane is communicating with Couer d Alene dispatch on a fire in North Idaho I believe. Anyone know what the situation is with Stevens county frequency being used?
I’m in Spokane lower south hill. I also have received the same thing on SDS 100. I Have it programmed for law only and I do receive Stevens county dispatch and mobiles from time to time.
thanks.
 

tvengr

Active Member
Joined
Feb 10, 2019
Messages
3,796
Location
Baltimore County, MD
CTCSS stands for Continuous Tone Coded Squelch System. In your case, there is a tone with a frequency of 203.5 Hz transmitted along with the voice audio. You don't hear the tone because it is filtered out. On receivers set to use that tone, the squelch will open up to hear only signals transmitting that tone. It is often referred to as a PL tone. Motorola calls it Private Line. GE called it CG for Channel Guard and RCA used QC for Quiet Channel. You can have several users on a frequency, and you will hear only the ones transmitting the proper tone. If you are using carrier squelch, any signal on that frequency will be received. You have probably noticed the noise on a FM receiver when no signal is being received. With carrier squelch, the noise is amplified and changed to a DC switching voltage which turns off the audio amp. When a carrier quiets the noise, it results in the audio amp turning on to hear the transmission. Using the squelch control, you adjust the level of noise necessary to switch off the audio amp.
 
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