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W6YX 2018 & 2019 Moon Bounce Adventures

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Published: 14 January 2020

  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



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     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.