SLR5700 Repeater Power Output Settings

[sjaltavilla]

I'm toying around with output power of my SLR5700 repeaters in a medium-sized three site Linked Capacity Plus system. My whole goal here is to make subscriber roaming as smooth as possible. All of my sites are relatively close together (we're talking less than two miles apart), so to state the obvious, there is overlap which I am trying to reduce. I have found what I believe to be the perfect roaming thresholds in the subscriber codeplugs.

But what's weird is that when I lower power on my repeaters, I'm actually getting more inbound range out of them. I'm no RF engineer by any means and I can't wrap my head around why binging the output from 50W down to 25W all of the sudden gives me better talk-in range. Worth noting that I am running a combiner setup at each site. Can anyone explain what factors might be at play here or the RF wizardry that causes this?

 

[buddrousa]

Why not move the sites further apart and cover a larger area with more customers?
That is because you are using CHEAPER DUPLEXERS and are suffering from DESENSE.

RF desense, short for radio frequency desensitization, refers to a situation where the sensitivity of a wireless receiver to incoming signals is reduced due to electromagnetic interference13. This interference can come from external sources or from stronger self-generated interference within the electronic system of the product itself1.


In telecommunications, RF desense is also known as receiver blocking4. It occurs when a radio receiver is unable to receive a weak radio signal that it might otherwise be able to detect when there is no interference4. This is typically caused by a nearby transmitter with a strong signal on a close frequency, which overloads the receiver and makes it unable to fully receive the desired signal4.


RF desense can lead to several issues in wireless communication:

 

[buddrousa]

Do your Duplexers look like these cost $100

Or do they look like these cost $3000

 

[sjaltavilla]

Thanks for the input. I'd love to move the sites farther apart, but we are only one business entity. Specifically a ski resort trying to cover a couple different valleys and two base areas.

This sounds like a good explanation as to why lower output power might be helping the issue though.

 

[sjaltavilla]

Do your Duplexers look like these cost $100

Or do they look like these cost $3000

The latter. TX / RX custom built.

 

[Firebuff880]

Thanks for the input. I'd love to move the sites farther apart, but we are only one business entity. Specifically a ski resort trying to cover a couple different valleys and two base areas.

This sounds like a good explanation as to why lower output power might be helping the issue though.

If the sies are mirrored from a Repeater stand point. I have found that converting a site into a voting receiver site with focused down tilt antennas is a better way to cover the Ski runs through a valley, where talk out from the Site works fine, but the radios just don't have the capability of getting over the terrain for Talk-in.

Use the data in your GPS/LRRP reports to do an RSSI study.

 

[RadioGuy7268]

The latter. TX / RX custom built.

TX/RX equipment is about as good as it gets, especially if the system was built and tuned to your specific frequencies.

What you're describing is quite typical of desense - ie: lowering transmit power improves receive function at the site. I'd be looking to have an actual tech with equipment pay a visit on-site and scope things out. I'm wondering if your antenna spacing is not what was originally spec'd - and I'm assuming that you are using separate transmit and receive antennas. If the TX/RX system was designed with a duplexer, then antenna spacing would not be an issue, as you would have only one antenna per site.

Next up, check cabling and connectors. Are you using quality jumper cables between the repeaters and the combiner system? What about any jumpers connecting to the antenna? TX/RX would have provided an intermod study with the combiners, does the system meet those specs for isolation between freq's? Were any operating frequencies changed since the system was ordered/built/delivered??

 

[kayn1n32008]

medium-sized three site Linked Capacity Plus system.

Define medium sized. How many RF channels per site?

My whole goal here is to make subscriber roaming as smooth as possible.

To do this, you really need to know the coverage of each site, and the overlap of each site to the other. This is easiest in coverage mapping software, BUT it requires someone who is competent using the software.

All of my sites are relatively close together (we're talking less than two miles apart), so to state the obvious, there is overlap which I am trying to reduce. I have found what I believe to be the perfect roaming thresholds in the subscriber codeplugs.

Thats tough. You may need to play with not only power, but antenna patter as well
To shape your coverage.

But what's weird is that when I lower power on my repeaters, I'm actually getting more inbound range out of them. I'm no RF engineer by any means and I can't wrap my head around why binging the output from 50W down to 25W all of the sudden gives me better talk-in range.

This isn't surprising. Power isn't the be all, end all of LMR. I've seen repeaters have upwards of a 80km Radius, 160km diameter of BALANCED coverage, on UHF, with 12.5w TXPO, with 11.5w into the feedline that was 350m in length. ERP was in the 20-25w range after system losses and antenna gain.

If you are on a ski hill, you are most likely using mostly portable radios, so having tons of TX power is going to make roaming a pain in the butt. Reducing your TXPO will actually help improve the subscribers roaming.

Worth noting, once you reduce power, you need to re-asses your roaming thresholds values to ensure your talk in coverage is balanced. You don't want to hold a site so long, you can't talk into it before you roam to a better site.

Worth noting that I am running a combiner setup at each site. Can anyone explain what factors might be at play here or the RF wizardry that causes this?

If you are using multiple RF channels per site, this makes sense. Are you using a single antenna at each site, or 2 antennas, 1 Tx, 1 Rx?

 

[sjaltavilla]

TX/RX equipment is about as good as it gets, especially if the system was built and tuned to your specific frequencies.

What you're describing is quite typical of desense - ie: lowering transmit power improves receive function at the site. I'd be looking to have an actual tech with equipment pay a visit on-site and scope things out. I'm wondering if your antenna spacing is not what was originally spec'd - and I'm assuming that you are using separate transmit and receive antennas. If the TX/RX system was designed with a duplexer, then antenna spacing would not be an issue, as you would have only one antenna per site.

Next up, check cabling and connectors. Are you using quality jumper cables between the repeaters and the combiner system? What about any jumpers connecting to the antenna? TX/RX would have provided an intermod study with the combiners, does the system meet those specs for isolation between freq's? Were any operating frequencies changed since the system was ordered/built/delivered??

Quality jumpers between repeaters and combiners: yes. Quality jumpers between combiner and antenna: debateable. Operating frequencies have not been changed since the system was ordered, built, and delivered. I'd have to look at the intermod study. I know the specs are different for each of our sites.

 

[sjaltavilla]

Define medium sized. How many RF channels per site?

Three repeaters, six time slots, two reserved for GPS and data.

To do this, you really need to know the coverage of each site, and the overlap of each site to the other. This is easiest in coverage mapping software, BUT it requires someone who is competent using the software.

I've got SmartPTT monitoring to measure inbound coverage from subscribers and a radio in a backpack with a laptop running MotoTRBO site survey for outbound coverage. Not great methods I will admit. Very difficult to tell what site a subscriber is roamed to in both softwares.

Thats tough. You may need to play with not only power, but antenna patter as well
To shape your coverage.

I think I've got this down on two of the three sites. I'm trying one thing at a time.

If you are on a ski hill, you are most likely using mostly portable radios, so having tons of TX power is going to make roaming a pain in the butt. Reducing your TXPO will actually help improve the subscribers roaming.

You said it. Pain in the butt indeed. Reducing power was always my plan anyways. No sense covering 50 miles north of the resort anyways. Hah.

Worth noting, once you reduce power, you need to re-asses your roaming thresholds values to ensure your talk in coverage is balanced. You don't want to hold a site so long, you can't talk into it before you roam to a better site.

I've got Roaming RSSI Thresholds set at like -65 dBm. I want them roaming whenever there's even a chance of the inbound transmission not making it.

you are using multiple RF channels per site, this makes sense. Are you using a single antenna at each site, or 2 antennas, 1 Tx, 1 Rx?

Single antenna each site. Was told that was the better option.


Side note: thank you all for your input and feedback on this so far. It is much appreciated.

 

[Firebuff880]

I've got SmartPTT monitoring to measure inbound coverage from subscribers and a radio in a backpack with a laptop running MotoTRBO site survey for outbound coverage. Not great methods I will admit. Very difficult to tell what site a subscriber is roamed to in both softwares.

It shouldn't be the Site and Repeater that handles the inbound LRRP (GPS) reports should be anoted -- Note: JSON is for Esri geoEvent & Velocity, Traccar and my Google map display. Does not show Crash Data or iBeacons but that data can be made available as well..

time          | 2025-03-31 21:54:56-04
gps_time      | 2025-03-31 21:54:50-04
srv_id        | 447
radio_id      | 842
device_id     | pcrid:447.842
email         | dapmt842@xxxxxx.dapage.net
alias         | FBW842
rssi          | -57.9185                <<<<<<<<<<<
site          | 1                            <<<<<<<<<<<
peer_id       | 9010                   <<<<<< Repeater 
request_id    | 52.1
report_reason | periodicReport
emergency     |
lat           | 43.604513 
lon           | -72.8201024
radius        | 6.4
alt           | 2762.6
alt_acc       | 9.3
speed         | 5.2
direction     |
climb         | 0
gpio          |
gpio_delta    |
raw           | \x.......................................................................................................................................................
serialno      | 427546955
json          | {"view": "Food & Beverage", "alias": "FBW842", "email": "dapmt842@xxxxx.dapage.net", "event": "periodicReport", "unitID": 842, "deviceID": "pcrid:447.842", "latitude": 43.604513, "reportID": 427546955, "longitude": -72.8201024, "poweredOn": true, "fixTimeUnix": 1743472490, "speedInKmph": 18.7, "organization": "XXXXXXXX", "eventTimeUnix": 1743472495.86573, "accuracyInMeters": 6.4, "altitudeInMeters": 2762.6, "signalStrengthInDbm": -57.92}
report_time   | 2025-03-31 21:54:55.865725-04