Will these channels interfere with each other?

[goldn_eagle]

A colleague of mine asked the below question / scenario and I couldn’t answer. I don’t know enough about P25 and trunking. Was hoping someone here could help.



Scenario:



Department A runs on channel 701.100 that is trunked. It has system keys, control channels, etc. But one of its main channels is 701.100. This is on a P25 radio system. Just your normal public safety setup. I know you have control channels and then TDMA or FDMA with + or - deviations. Motorola radios being used.



Department B also has P25 Motorola radios and uses 701.100 on P25 for car to car communications. Not trunked and no repeater. Just a channel they use for car to car.



Will 701.100 work for both departments? Or will there be some kind of interference?

 

[KevinC]

How close are these imaginary agencies that your friend is asking about?

 

[Whiskey3JMC]

Isn't there usually frequency coordination before licenses are issued to prevent such scenarios from happening?

 

[goldn_eagle]

How close are these imaginary agencies that your friend is asking about?

Not sure, he didn’t specify. We can call it within 10 miles of each other.

 

[goldn_eagle]

Isn't there usually frequency coordination before licenses are issued to prevent such scenarios from happening?

I’m sure there is…this was just a scenario he came up with to figure out if there would be interference between the 2. I don’t think this is meant to get too critical / in-depth with “frequency coordinators”.

 

[KevinC]

I’m sure there is…this was just a scenario he came up with to figure out if there would be interference between the 2. I don’t think this is meant to get too critical / in-depth with “frequency coordinators”.

Not sure, he didn’t specify. We can call it within 10 miles of each other.

Maybe, maybe not. A lot more info would be needed. Maybe get your "friend" to join RR and have him ask directly so nothing gets lost in the back and forth between you two.

 

[goldn_eagle]

Maybe, maybe not. A lot more info would be needed. Maybe get your "friend" to join RR and have him ask directly so nothing gets lost in the back and forth between you two.

 

[goldn_eagle]

Sure thing! Will ask him to sign up and re-ask the question. Thanks for all your input everyone!!

 

[otobmark]

Yes they will interfere but real world question is will anyone actually notice. I’m pre coffee at the moment but isn’t 701mhz the repeater output? If so, TRS (Dept A) cars might never notice the simplex unless very close to dept B car while both happen to be using 701. I would think dept B would have bigger problem since dealing with a high power repeater output which can cover 10 miles with hefty clout. I don’t know size of TRS (channels) or loading but the odds of both A & B subscribers being very close and actively using 701 might not be likely, and simplex users (B) are accustomed to imperfect connections.
REAL WORLD: Neither agency may care. It is a bad practice of course.

 

[goldn_eagle]

Yes they will interfere but real world question is will anyone actually notice. I’m pre coffee at the moment but isn’t 701mhz the repeater output? If so, TRS (Dept A) cars might never notice the simplex unless very close to dept B car while both happen to be using 701. I would think dept B would have bigger problem since dealing with a high power repeater output which can cover 10 miles with hefty clout. I don’t know size of TRS (channels) or loading but the odds of both A & B subscribers being very close and actively using 701 might not be likely, and simplex users (B) are accustomed to imperfect connections.
REAL WORLD: Neither agency may care. It is a bad practice of course.

THANK YOU! This is what I was trying to explain to him….that it, in theory, it might work…but it would be terrible practice. The 701 mHz was just a made up frequency…it could be anything up in that mHz range. In the end, I think the biggest question was around if a specific frequency is trunked is it vulnerable to interference from that same frequency untrunked.

 

[KevinC]

Yes they will interfere but real world question is will anyone actually notice. I’m pre coffee at the moment but isn’t 701mhz the repeater output? If so, TRS (Dept A) cars might never notice the simplex unless very close to dept B car while both happen to be using 701. I would think dept B would have bigger problem since dealing with a high power repeater output which can cover 10 miles with hefty clout. I don’t know size of TRS (channels) or loading but the odds of both A & B subscribers being very close and actively using 701 might not be likely, and simplex users (B) are accustomed to imperfect connections.
REAL WORLD: Neither agency may care. It is a bad practice of course.

701 would be band 85 uplink...but I believe the frequency was just made up as an example.

 

[otobmark]

701 would be band 85 uplink...but I believe the frequency was just made up as an example.

In that case there will be a problem especially for Dept A.
Side question: If affiliated radio is sent to a frequency it cannot get into because of interference or whatever, what happens? Is TG reassigned to new channel?

 

[chief21]

Side question: If affiliated radio is sent to a frequency it cannot get into because of interference or whatever, what happens? Is TG reassigned to new channel?

In most trunked radio systems, if the system sees interference or detects a failure of a voice channel, that channel would not be assigned until the problem clears.

 

[xmo]

Should never happen. Public safety licensing requires coordination.

 

[Echo4Thirty]

In most trunked radio systems, if the system sees interference or detects a failure of a voice channel, that channel would not be assigned until the problem clears.

The system would never see interference if someone was talking direct on the output of the base stations as it has nothing listening to the output frequencies. Illegal carriers occur because the system is detecting interference on the inbound path, be it atmospheric or radios transmitting on other systems. When I was in FL, we had a couple of channels get clobbered by subscribers on other systems 100s of miles away during tropo ducting, and we were 800 MHz!