Team W6YX has a been chugging along, participating in the annual ARRL Earth-Moon-Earth (EME) contest. The contest consists of three weekends. The first weekend is for frequencies above 2GHz, usually in September. In October and November are two contest weekends for amateur radio frequencies bands below 2GHz. The goal is to contact as many stations as you can using the surface of the moon as a passive reflector. Voice, CW, and digital communication modes are
used. We built from scratch, modified existing designs, modified existing hardware, modified existing code or wrote code from scratch to build our 5 band EME station. W6YX regularly contacts stations around the world via a lunar path using 10.368GHz, 2.304GHz, 1.296GHz, 432MHz and 144MHz.
Our team has been busy in recent years with non amateur radio aspects of our lives. This has prevented us from putting on a 5 band contest effort. Due to time constraints we didn’t give a 2018 update, so it’s fitting we start there. Our unexpected issues from 2017 continued. As summer of 2018 was ending we decided to optimize our 10GHz station. Usually we pick a project to concentrate our efforts on before the EME contest. Knowing our beam pattern will give valuable information in determining why our dish is performing notably worse than what it’s theoretically capable of. We setup a signal generator feeding a dish 5km away.
We scanned the vicinity of this signal source using our 4.6m dish in 0.1º increments, measuring its amplitude using Linrad’s excellent signal level measurement functionality. After several hours spent painstakingly manually scanning, we had a spreadsheet full of data points used to produce a plot of our dish’s beam pattern.
The pattern alone did not explain the lack of expected performance. With no single or easy point of optimization we could complete before the contest, we decided to enter our station into the contest as-is.
While testing our 10GHz station, we noticed our echos off of the moon were greatly attenuated.
Further inspection showed a critter had crawled and nested in our feed horn. Unfortunately it did not survive the dielectric heating during the transmission periods of our TWT amplifier. The remains were too charred to identify the species of the critter. The melted Kapton wave guide seal (over 400ºC/750ºF) gave indication of the temperatures involved.
Fortunately this issue was easy to repair.
Unfortunately right before the start of the contest, our dish elevation system exhibited failure resulting in very high elevation motor current draw. The current draw caused the failure of a 2ohm 100W current limiting resistor in series with the motor. We found a temporary solution by placing the manual mechanical brake part way between the on and off position. This allowed the failed braking system just enough pressure to keep the dish from falling in elevation, but not too much brake pressure that the motor couldn’t over power. We couldn’t simply bypass the current limiting resistor to the motor with out spending time recalibrating the controller used to drive the motor. To replace the blown 2ohm 100W resistor, we found some stranded wire cut to a length that resulted in 2ohms. Unfortunately the wire jacket was not able to withstand the 260ºC temperatures the motor drew, even with the brake partially released.
After charring this makeshift wire resistor, we ended up putting together a combination of power resistors in series and parallel to produce 2ohms. However, this also proved ineffective, as the resistors quickly began to overheat. An elegant solution was found. We placed the resistors in a bucket of water. If the water didn’t boil, we knew the resistors were safe, under 100ºC.
After these hurdles and missing the first night of the contest, we were able to make it back on the moon the second night and scored a respectable 2nd place in the multi-operator, all mode, 10GHz category. Our team has worked extremely hard over the years building our station in capability, bands, reliability and usability. Team W6YX’s ARRL EME contest performance over the past 7 years reflects this.
2012- 4th place in the multi-operator, all mode, all band category
2013- 5th place in the multi-operator, all mode, all band category
2014- 2nd place in the multi-operator, all mode, all band category
2015- 1st place in the multi-operator, all mode, all band category. Would have placed top three in each of our 5 bands if our efforts were divided.
2016- 1st place in the multi-operator, all mode, 1.2GHz category
2017- 1st place in the single-operator, CW mode, 1.2GHz category
2017- 2nd place in the multi-operator, all mode, 10GHz category (using the call N9JIM)
2018- 2nd place in the multi-operator, all mode, 10GHz category (using the call N9JIM)
2019- Projected based on electronic logs received: 1st place in the multi-operator, all mode, 1.2GHz category (using the call K6MG), and 2nd place in the multi-operator, all mode, 144MHz category
In 2019 team W6YX had another successful ARRL EME contest. We put in a more limited effort this year, operating 1296 and 144 MHz. The contest was not with out its share of unexpected surprises. We had planned to also operate our 10GHz station, but a last minute elevation position readout issue prevented us from getting our 10GHz signal on the moon for the first time in 5 years. Our elevation syncro position to digital converter box developed a strange intermittent offset.