This past weekend I met three other hams at the Synopsys site in Hillsboro to install our group’s D-STAR repeater. We have had the components of this stack for a while now and have been testing it at a low-level site (my house). Late last year, a member of our group approached the Synopsys facilities supervisor about potentially locating some or all of our D-STAR repeater equipment on their roof. They graciously agreed and we closed on that this weekend.
We installed a Comet GP-98 antenna on a ten-foot pole with a very short run of 9913 coax through the wall into the roof stairwell enclosure. Inside, we put a 7′ fully-enclosed rack cabinet with our D-STAR repeater controller, UHF RF module, and our UHF duplexer cans from TX/RX Systems. We got everything installed and set out to test things to make sure they worked properly.
Initially, we were getting almost no power output from the repeater past the duplexer, but full output into a dummy load. Not looking to prolong the installation day too far, we decided to tune up and install a small mobile notch duplexer that I happened to have with me so that we could at least get the machine on the air and then go home and diagnose the issue with the large duplexer offline. Performance with the notch was not good at all, and I was worried that there were other issues at play. Anything but the strongest signals into the repeater were seriously garbled and absolutely no data traffic was making it through the unit.
At home, we were able to determine that while the duplexer cans were tuned perfectly for our transmit frequency, they were presenting a relatively high SWR to the repeater PA, which caused it to scale back its power dramatically (from about 20W to 2.5W or so). We retuned the duplexer a bit to give an additional 1db of loss but with very low SWR. I tested it on a ground-level repeater module and confirmed that it was putting out reasonable power again.
On Wednesday, I returned to the Synopsys site to reinstall the better duplexer and do a little bit of testing. With a wattmeter, I was able to confirm that the repeater was putting out a reasonable amount of power after the duplexer. After calling on the air for testers, it was immediately apparant that it was performing significantly better with the cans than the notch filter. More testing that day and the day after was extremely positive. Mobile stations were getting into the repeater quite well, and almost all fixed stations could hit it easily at 5W, even with a handheld on a rubber duck. Wednesday night, I was able to have a QSO *and* transmit GPS position reports clearly from PDX Airport some 18 miles east. Thursday morning, another station was able to get into the repeater easily while mobile from the intersection of Highway 6 and Highway 8, about 20 miles west. Quite impressive for a repeater that is only six stories off the ground and putting out about 15 watts after losses!
The machine is KD7RFI_B on 440.550+MHz. There is no gateway on it (and we’re not sure if we will try to install one at this site or not) at the moment. If you’re within range, jump on and say hi!