Flagstaff police gone???

[citylink_uk]

here's a sample clip of the odd tone that I'm talking about. It only occurs when the dispatcher is talking.

http://www.simcoa.org/KDX3CB/sample.WAV

Any ideas?

Heard this on many systems in the US. Its perhaps something to do with the audio console?

Rich

 

[kd7ckq]

Sure thing. Heard a two second tone followed by details like Person X stabbed followed by the location. or Two second tone follewed by Fight in progress location Y with bats.
I'll try to confirm it this weekend.

 

[wlmr]

here's a sample clip of the odd tone that I'm talking about. It only occurs when the dispatcher is talking.

http://www.simcoa.org/KDX3CB/sample.WAV

Any ideas?

This is called tone controlled keying (used for dispatch transmit)

You're actually hearing three tones. 125 milliseconds of 2175 Hz High Guard at a strong level, 40 milliseconds of 1950 Hz Function Tone commonly -10dB down in level from High Guard, and a continuous 2175 Hz Lo Guard tone commonly at -30 dB down from High Guard for the duration of the dispatcher's transmission.

(These are the most common levels, frequencies, and durations that I know. Different manufacturers have slightly different standards - what a suprise.)

The dispatch console has been set up to remotely key up a base station via the use of control tones- either correctly for something connected in parallel - or incorrectly if the radio uses some other type of transmit control.

The first tone is sent and decoded by the base station to let the radio know that the next audio it hears will be a control tone. Second tone tells the radio what to do - like key up and transmit on it's Frequency 1. The final and continuous tone is there to let the radio know to stay keyed up while the dispatcher is talking.

This type of keying is used so the TX audio path to a remote transmitter also carries the key up and un-key info for the remote radio.

FCC (and common sense) says that if you don't have direct control of a radio's PTT, you need to set your control up so that if contact with the radio is lost the base radio will release it's PTT. As soon as the continuous tone stops (or the audio path is lost) the radio should un-key.

The circuitry in the remote transmitter not only can decode these tones but also removes them from the transmit audio path. You're hearing them either because the tone notches aren't working or this type of remote transmitter is using some other method of transmit control and the console wasn't correctly set up. There's other possible reasons but I'm getting tired of typing.

Is this being heard on the Flagstaff PD talkgroups?

 

[kd7ckq]

There is a little ping if the units answer each others in rapid succession. I don't think it is as bad as that audio clip.

 

[KDX3CB]

The audio clip was from flagstaff PD a few days ago. It is NOT happening anymore though. Thanks for the info!