Repeater Channel Busy with no Traffic

[pboyd04]

I have an XPR8400 running R02.40.01. Every once and a while I will try to key up the repeater (either time slot) and will get a busy signal. The funny thing is, looking at the repeater neither transmit or receive light is on.

Troubleshooting I've tired:
1. Pulling the duplexer and using two antennas - same issue (so I think I've ruled out the duplexer)
2. Switching to another frequency pair that I know works because that repeater doesn't have this issue - same issue (so I think I've ruled out client programming)

I can work around the issue by programming the client radios' Admit Criteria to "Always" (even "Color Code Free" has the same issue), but that feels like masking a problem. Anything else I should try?

 

[Mars]

What's the noise floor on the RX frequency at the site?

What do you have the RSSI Threshold (dBm) set for in the repeater channel configuration? You may wish to increase the threshold so this field is not being triggered. (To rule it out, temporarily set it to -40 dBm, then use a realistic value if this resolves the issue).

 

[pboyd04]

Sorry, I'm not sure how to measure the RF noise floor. When I pull it up on a spectrum analyzer it looks pretty good when the repeater is off. I've also tested the other repeater on this frequency pair with no issues. And have used these repeaters at two different sites more than 60 miles from each other.

I just tried cranking the RSSI on the subscriber to -80 dBm (the maximum CPS will let me set) and had the exact same issue.

 

[Mars]

Sorry, I'm not sure how to measure the RF noise floor.

Use RDAC. You can sample the noise floor of each timeslot, or look at the analog equivalent if operating in that mode.

I just tried cranking the RSSI on the subscriber to -80 dBm (the maximum CPS will let me set) and had the exact same issue.

I asked you to try adjusting the RSSI Threshold in the repeater channel configuration, not the subscriber. The subscriber RSSI is for IP Site Connect roaming.

Here's the RSSI Threshold help context for the repeater:

RSSI Threshold (dBm)

This threshold defines a level at which the repeater will not transmit due to interference. For a multi-repeater trunked system this threshold also determines the level at which a repeater will temporarily remove itself from the system due to interference. IP Site Connect Systems The threshold should be set according to any license restrictions (for example FCC), increasing the level will make the repeater increasingly impolite to other systems. Capacity Plus Systems and Linked Capacity Plus Trunked Systems When this threshold is exceeded by an unwanted RF signal then the repeater will be temporarily removed from the system. When the interference falls below this threshold the repeater will return. This happens very rapidly. Dealers should estimate the level of interference and set this level accordingly; setting the level too high will result in wanted signals not being received when interference is present, whereas setting the level too low will result in a loss of channel capacity. This is a channel-wide feature.

 

[pboyd04]

That field is grayed out on the repeater... Any idea what other setting I need to change to enable it?

 

[Mars]

That field is grayed out on the repeater... Any idea what other setting I need to change to enable it?

It will remain greyed-out if you have the IP Site Connect (timeslot selection) set to "none". If you are using IP Site Connect (I assumed you were, since you mentioned multiple sites), then this field should be set to whatever networked timeslots you're using.

Send me your codeplug. marsp25 at gmail. I'll look over it to see if there's something not set properly.

 

[pboyd04]

Sorry when I said multiple sites I didn't mean to use the overloaded term sites. I meant that I have moved these two repeaters to two different locations with the same results.

 

[pboyd04]

Ok even with IPSC enabled and the RSSI cranked to -40 I still have the issue. According to RDAC the RSSI is around -105 to -110... So what else can I try?

 

[Mars]

After reviewing your codeplug, I could not spot any errors. However, further troubleshooting for you:

- Upgrade the repeater firmware from R02.40.01 --> R02.40.20 (current as of this post)
- Upgrade your subscribers to R02.50.05 (second gen) or R01.12.17 (first gen)
- Make sure your color codes match (repeater and subs)

Off topic but worth mentioning:

- Your noise floor of -105 to -110 dBm is quite noisy. Consider installing a preselector or find the source of the noise at the site.

Are your noise floor readings from an idle repeater or an active repeater? Does the noise floor change considerably (-130 dBm on idle to -105 dBm) during TX? If so, consider a duplexer retune, as it's not normal to increase your noise floor by ~25dBm when the transmitter is active.

If your duplexer is fine, you can't locate a local noise source and there's no change when you TX/RX, the preselector will increase the range of your machine. You'll see about -1.1 or -1.2 dB insertion loss, but you'll gain 5 or 6 dB of quieter RX. Your repeater can go as low as about -122 dBm and recover workable DMR signals. But if they're hiding in that -105 dBm noise floor, you're losing range.

 

[pboyd04]

I'm still trying and failing to update the Repeater firmware (see the XPR8400 update thread).
My subscribers are all at the latest firmware.
The color codes do match.

The repeater is idle for those readings. If I read RSSI while active I get closer to -45 with or without the duplexer. I'm transmitting from about 40 feet from the antenna if that makes a difference. So what could be the problem if I've ruled the duplexer out?

 

[Mars]

Unscrew the BNC jumper on the RX port of the repeater. Do another measurement. What is the noise floor now?

-45 dBm is extremely strong. I assume this is the measurement you are making (from repeater) when you're receiving your subscriber? If this is your RSSI Reading, with no receive signal, simply when the repeater is transmitting, you have a problem with the receiver in the repeater.

 

[pboyd04]

If I switch to my other repeater on the same frequency pair then I get an RSSI of about -125.

Without the BNC connected I get an RSSI of -118 to about -120. The -40 is while receiving from the subscriber. While just transmitting it only goes up to about -117.

 

[Mars]

Have you checked the alignment of this repeater and the subscriber radios?

 

[pboyd04]

No I haven't. Is this the same as tuning the repeater or is aligning something else?

Sorry, if this is really basic... these are my first repeaters...

 

[Mars]

No I haven't. Is this the same as tuning the repeater or is aligning something else?

Sorry, if this is really basic... these are my first repeaters...

No, alignment will involve you taking the repeater to an alignment specialist. I recommend a tire rotation at the same time.

 

[pboyd04]

Awesome, I will make sure and pick up some headlight fluid while I am at it...

 

[pboyd04]

If I understand you correctly, you suspect there is something either wrong or at least misaligned with the hardware and I need to get this repeater serviced?

Is that correct?

 

[Mars]

If I understand you correctly, you suspect there is something either wrong or at least misaligned with the hardware and I need to get this repeater serviced?

Is that correct?

Yes, if everything is programmed properly, I would suspect a hardware problem or an alignment issue with the hardware.

 

[Bill_G]

A noise floor of -105db antenna connected, and -120b ant disconnected, but not duplicated at other sites that use the same freq pair suggests further investigation needed at *this* site to determine source of interference. You may have to bring in a pro, or someone with more experience to assist. A spectrum analyser won't be very useful. They generally have a rcvr threashold of -100dbm which is slightly above where this interference lands, and won't be seen by the test equipment. You'll have to use a service monitor sig gen, mobile rcvr, iso-tee, and a directional antenna to fox hunt the source.

It may be on site (radiating from another piece of equipment), or it may be off site but close by . Or, it could be very far away with a lucky shot to your antenna based on terrain. Good luck.

 

[Bill_G]

Here is an example of a far away station with a lucky shot to our receiver causing grief. It was 41 miles away constantly keyed. Dead carrier. No CWID. Put up by our state police technical services to burn in a new xmitter. They are licensed, and operating at rated power - 8W into 3db omni - from the second story roof of their office. Nailed our rx antenna really well, but could barely be heard on the ground. The path profile proved I should be able to hear it on a handheld. But! I had to be in the right square foot to find it. Drove me nuts for part of a day triangulating on it. It took me a bit to realize it was further away then I first thought.