I will attempt to ramble on about my repeaters.

My first attempt was to build an analog repeater using 2 TYT-9000D UHF radios, an ID-O-Matic IV controller and a "Chinese special" notch type duplexer. Long story short, the TYTs poorly built and the TX radio desensed the RX radio so bad I couldn't get a 1/4 mile range. I thought it was the Chinese duplexer, picked up a used Phelps Dodge BpBr duplexer, didn't help. The controller then died so I scrapped the project and parted it out. I also found out the used duplexer I picked up was burnt up internally from high RF power.

My second attempt was building a MMDVM repeater out of several old Motorla GM300s with various issues that were given to me. I used the STM32-DVM board from Scott Zimmerman, N3XCC, and the "Chinese special" duplexer. One of the GM300s, the PA deck was dead, and the other was on the way out only putting out 7 watts. I was only about to get about 2 miles out before the repeater went deaf. While I was considering winging a Celwave/RFS mobile duplexer or an RX preamp for troubleshooting, the GM300 PA deck took a dump and died. I purchased a used CDM750 and put it in the repeater. I felt terrible about wasting such a decent radio in a repeater that worked poorly.

One day, I noticed the repeater was working so poorly and after testing the RF output, I was getting roughly 10 watts out of the duplexer. The radio was set to put out 25 watts and before I was getting 16 watts after the duplexer. I checked the SWR of the duplexer and found it had jumped to 2.2:1 and no amount of tuning fixed it. I also tested the CDM750 power out and found it was only putting out 17 watts, and not the 25 it was set to. At this point, after killing 2 radios, I was dismantled the repeater and gave it the middle finger.

By this point, it was late December of 2020 and after have started my first repeater attempt in April of 2020 with no success, I took a vacation from repeater building. During this time, I was able to fine tune my duplexer tuning procedure and get the "Chinese special" duplexer tuned properly. I also fixed the power output on the CDM750, turns out the power calibration was off due to a faulty mini-UHF cable.

In mid-February, I was cruising eBay and found a Motorola XPR8300 403MHz-470MHz 48 watt repeater that wasn't stupidly overpriced so I picked it up. Buying a used XPR8300 is rather risky, these repeaters were known for blowing the finals right and left. There are numerous design flaws on them ranging from bad thermal transfer installs and the main flaw, the fan speed being controlled by ambiant temperature inside the repeater and not based on the TX final temperature. My unit was owned by a HAM before and had the fan modded to run at full speed. I performed a TX power tuning and threw it on the air with my "Chinese special" duplexer and was blown away. My external antenna is a magmount up 25 feet on a chimney cap and I was seeing mobile coverage 7 miles north of my house and handheld coverage over 2 miles to the east. I was estatic, my China duplexer performs perfectly. The XPR8X00 repeaters have very hot receivers confirming my suspicion that the GM300s are very poor receivers. I ended up replacing the thermal paste/pads and set the repeater to 20 watts, which is the MAX the 8300 repeaters should ever run and the fan needs to be at full speed too.

I ended up doing some more research into the PA failures of the XPR8300s compared to the XPR8400s. SPOILER: The XPR8400s are much better. The XPR8400s can survive running full power at 100% duty cycle without a fan but as a rule of thumb, run them at NO more than 25 watts and the fan also at full speed. Anyway, I came across as post discussing the UHF R2 XPR8400s that are 450MHz-512MHz and how you can't hexedit the codeplug into HAM frequncies. I quote, "the repeater is fucked" when you perform this hex edit. You can read more about it here, I won't get into the technical details here.

So what do I do? Headed to eBay and found an XPR8400 UHF R2 for $400 and purchased it. I threw it on the bench and hex edited the code plug and move it to 444.975MHz for TX and 449.975HMz for RX, the highest repeater pair in the band plan. I started in analog and it went well other than the repeater only putting out 9 watts when it was set to output 15 watts. This was one of issues that one could run into according the forum post. I ran a power calibration and guess what? I got 15 watts out on the dot when I tried again. With this success, I switched the repeater over to DMR and hooked it up to Brandmeister and it worked like a charm, producing some of the best DMR audio I have ever heard.

Excited by all this, I retuned my duplexer in under 2 minutes and threw it and the repeater on my antenna, programmed my radios and hopped in the car to see if the claim of poor range is true. SPOLIER: I ended up having to abort the range testing it was working so well. To the south of my house, I was able to get just over 6 miles of handheld coverage and 14 miles of mobile coverage, and I could have gone farther. I get home and check the Brandmeister page and found the repeater was hearing me at an S6 while 14 miles away, even with my crappy house antenna. I am burning up most of my TX power on the antenna feedline, that is going to be fixed in warmer months so the repeater should work even better.

In conclusion, the R2 XPR8400 worked quite well despite what the data says.