P25 Intellirepeater System Software Setting Question

[Wadsworth]

Hello,

I need a quick answer to the following, when setting the "minimum allowed carrier" in a transceiver for a P25 Intellirepeater, doesn't that setting apply to all signals coming into the system. I'm being told that it only applies to "illegal carriers" and has no effect at all for customers. In my experience, setting that value, or the minimum allowed carrier level to a low value allows weaker signals from portable radios to get through, raising it to a higher number, i.e. from -90 to 75 is in effect reducing what can get through by 15 dB but I have a Motorola tech swearing it makes no difference to users, only to interference when the illegal carrier lockout is set to on.

Any insight to why I'm being told it won't make any difference to set the minimum allowed carrier level to a lower or higher level for users?

Thanks!

Chris

[Wadsworth]

I should have added, this system uses GTR8000 P25 repeaters.

[xmo]

Is this an Astro 25 7.X system?

[Wadsworth]

Yes, 7.X

[xmo]

If you don't quite trust what you're being told, you could test it to see for yourself.

Assuming you have administrative rights, use Channel Partitioning to map a test radio and test talkgroup to one of the channels and restrict it so that no other users are granted that channel.

Then connect your test radio to the site's test antenna. Connect a spectrum analyzer to the receive multicoupler so you know the exact signal strength that the GTR is receiving from your test radio.

Then insert a variable attenuator in line between the RMC and the GTR. That way you can reduce the signal to any level you want to see how the system performs with various settings of the parameter in question.

This will probably take two people, one at the master site to enter the changes & push them out and one at the GTR site to run the test equipment.

[Wadsworth]

Thanks,

Appreciate the suggestion, I very well may end up doing just that. I've adjusted the minimum allowed carrier level setting before and we did seem to make a difference for low signal level carriers, but a Motorola Guru from batwing corporate is telling me it only applies to illegal carriers alone, but to me, that doesn't make sense, an illegal carrier is an illegal carrier and should be disregarded anyway, weak or not. However, he keeps telling me I'm wrong but practical tests done months ago indicate otherwise. Still, he has got me questioning this now and need to confirm one way or another!

Chris in Afghanistan

[xmo]

This is part of what it says in the book:

Illegal Carrier Determination – The illegal carrier determination feature allows the channel to detect and respond to unrecognized signaling on the channel that exceeds a particular threshold for at least a certain amount of time. This feature can be enabled or disabled through this parameter.

For more information see “Illegal Carrier Determination Feature” in Chapter 7. The RF Threshold Level and RSSI (Receiver Signal Strength Indicate) values are referenced to the input of the Receive Multicoupler.

◦ Enabled means that the system can detect an Illegal carrier, using the value in the RF Threshold Value (dBm) field.
◦ Disabled means that Illegal Carrier Determination is disabled and the system uses the –90 dBm value in the RF Threshold Value (dBm) field. If this field is disabled, the Malfunction Timer Value field is set to 254 and grayed out.

• RF Threshold Value (dBm) – The RF threshold parameter determines the minimum RF signal level that will be recognized before classifying an illegal carrier event and reporting an alarm to Unified Event Manager.

[Wadsworth]

Thanks, wish I had that book, it has gone missing here. I will test it to make sure this is how our system acts because I've heard of other things in a Motorola system which are not as we are told they should function, even by Motorola. If the above is reality, it appears the reason I am able to get better performance with the minimum allowed carrier level setting at or below the noise floor is due to the channels locking out when set lower than -85 dBM due to locally generated jamming/ECW. I surmise, if the channel won't lock out, then the situation is a "who ever has the most power in channel bandwidth wins" situation, the user or the jammer which explains why the system will often allow weaker signals through when set up that way, although at such a low signal to noise ratio we then have digitizing distortions as the decoder can barely demodulate the audio, as the desired but weak carriers compete with RFI which would normally lock the channel out.

[xmo]

The 7.X documentation is available for download in the Resource Center area on MOL.

Here is a procedure you can use if you decide to run further tests:

"Channel Partitioning can be used as a troubleshooting aid in tracking down and resolving channel-specific problems. This can be done by using its capability to steer specific groups or radio units to a specific RF channel resource, while restricting all other groups and radio units from the same RF channel resource. With Channel Partitioning, it is possible for the troubleshooter to be granted the same specific RF channel resource on every channel grant. The restriction of other users from this channel also allows the maintenance organization to quickly accomplish their troubleshooting without waiting for other users that might otherwise be assigned to the channel being tested."

[Wadsworth]

Thanks much!