April & May Engineering Committee Notes

If you have spent any amount of time on the 2m SLSRC repeaters, you’ll know we’ve been battling issues with the 146.970 repeater.  In the past 9 months we’ve upgraded quite a bit of equipment on the 97 repeater to help coverage and also introduced C4FM digital into that system.  Back in Sept 2018 we replaced the coax, upgraded the antenna and also installed a Yaesu DR-1X repeater in AMS mode at the site. For months this repeater was working great, but in 2019 we started having issues.  

As mobiles travel around STL, these stations and other weaker stations have experienced a chopping effect, dropping the receiver about once per second for a total of 8 to 10 seconds segments at a time.  As you can probably tell, if you have an unreliable repeater, radio operators are going to lose faith in that repeater and take their conversations elsewhere. The engineering committee has seen a dramatic drop in activity on this repeater since in 2019.

Here is an example video of the chopping users were experiencing on the repeaters (this is not the 146.970 repeater).

After multiple trips with Joe (WØFY), troubleshooting, brainstorming and lots of emails back and forth between the engineering committee members, we think we’ve finally found a root cause of the chopping.  It’s a case of repeater desense. What is repeater desense? It’s basically a receiver becoming deaf to an outside signal or it’s own signal getting back into the system.

How do you test a repeater for desense?  Below is a sample video of checking for desense if you want to learn more about the process.

During our May repeater work day, George (WBØIIS) led a group of committee members to help test for repeater desense.  After connecting the repeater to a communications service monitor we were able to recreate the chopping issue pretty reliably.  Because it was raining we were not able to remove the antenna to figure out at what point the desense is happening, but we have ruled out it’s not between the repeater and duplexer cans, or the duplexer.  This leaves the point where the coax connects to the antenna. We’ll need to go back in June after schedules come together to do more testing, but it’s looking better for that repeater as we are getting to a root cause.  I’m hopeful by July we’ll have that repeater in full service again.

Also in June, the committee will travel to the 9666 Olive site to work on the 146.850 repeater.  We will be replacing the CAT1000 repeater controller for a brand new CAT800 controller with Internet access.  We’ve been testing our AllStar nodes and we will put node 40105 with Echolink service (our Echolink node number will not change) on the 146.850 repeater.  This is the first step in our repeater linking project. We have some cool things planned for the rest of 2019 so stay tuned as we will announce more upgrades and changes to better serve the amateur radio community with the SLSRC repeaters.

On a side note, a few of the engineering committee members meet monthly with other area repeater owners to talk about promoting System Fusion in the STL area.  The committee has completed quite a bit of testing with new technology that we are excited about announcing soon, so stay tuned.

The past month has been slow due to troubleshooting issues at the 146.970 location.  As we move into the summer months and get the 97 repeater up and working correctly, we’ll get back on focus with building out the AllStar network and start testing the AREDN network at each repeater site.