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My other hobby, ham radio
Mary B:
Right now about all you will get on CB is some E-skip and that season is ending. With the sunspot cycle winding down F2 propagation is becoming rare on the upper bands.
Mary B:
Moonbounce is a lot of tinkering, a lot of building, technical challenges etc and that is why I do it!
--- Quote from: SparWeb on December 16, 2015, 01:18:53 AM ---You can seriously communicate with Earth-bound stations by bouncing off the moon?!
OMG... googled it: 250 dB losses from sender to receiver.
"We choose to radio the moon, not because it's easy, but because it is hard."
Stop before you infect me. I have enough hobbies!
--- End quote ---
ChrisOlson:
--- Quote from: Mary B on December 19, 2015, 06:09:55 PM ---Moonbounce is a lot of tinkering, a lot of building, technical challenges etc and that is why I do it!
--- End quote ---
EME is not something you just do and it happens by chance. I got three successful EME's in September on 6 meters working in partnership with a station in Norway. We used JT9 on wsjtx software, I used a nine-element (all elements driven) dipole array with three elements at 1/4 wave spacing front to rear driven successively at 90 degrees out of phase, and stacked three high at 5/8 wave stacking. The station in Norway used two 9 element yagi's stacked at 5/8 wave. We ran about 800 watts of power.
My dipole array is useless for other normal communications because the front lobe off it is like a flashlight beam. If I point it at you - only a few degrees off and the signal misses you. The beam is so tight it will just about set trees on fire on the horizon. Like Mary said, it takes a lot of tinkering and building - I spent most of the summer with the analyzer adjusting phasing lines, phase spacing and stacking to tune up the array. I worked with another station about 110 miles away in Rhinelander for the tuneup. And then when the day comes the moon has to be visible at both locations (which means only at moonrise into Europe from the US) and weeks worth of preparation and work last about one minute each way for each successful EME contact. And even then it takes a lot of luck because the surface of the moon is not all that smooth and tends to scatter your reflected signal.
We were using only a 20 Hz pass filter on the receiver front ends for a 16 Hz wide signal. And the timing has be precise, +/-60 ms, sync'd with an atomic clock between the two stations. Almost 100% of the amateurs doing EME on 6 are using linux to drive the rig because Windows isn't accurate enough and does not use the Unix Epoch clock for timing. Few people are doing EME on 6 because of the path loss and technical difficulties. But it was still a lot of fun. Our next attempt will be in February, working with the same station in Norway, and in concert with another station only about 4 miles from me that has built an experimental 6m wireframe parabolic reflector.
Mary B:
Hard part on 6 is engineering the support structure for such large antennas. I had stacked 5 element beams on 6 on a 17 foot mast... mast finally failed in one of my many windstorms. Bent 30 degrees. Luckily that tower also cranked down and tilted over so I could salvage the antennas. Since it was a rotating tower I moved one of the antennas to a lower section but that out it at 21 feet so not as effective. That tower finally showed enough wear that I had to retire it. Where it rotated was steel on steel and it had worn a deep groove...
W7GJ's 6 meter eme array... lots of engineering and I do believe it failed recently...
ChrisOlson:
That's why I went with the dipoles instead of yagi's. Stack up three elements on a driven array at 1/4 wave spacing, with each element driven 90 degrees out-of-phase in succession and the f/b ratio is VERY impressive. Another station only 5 miles away transmitting at 100 watts can't be heard on the back side of a three-element driven array. The phase cancellation, once tuned to perfection, is 100%. And the whole thing is only 10 feet long, front to back. But it's 23 feet high once you add two more three element driven arrays at 5/8 wave stacking height to get the azimuth angle down tight.
You can't just turn that array - it has to have azimuth tracking as well. And to get maximum ground gain on the ground plane radials laid out in front it, pointing east, the bottom elements have to be precisely 19.6 feet from ground. So from ground level the whole thing is 43 feet high. I welded an old satellite tracker to the end of a 20 foot long piece of 4" x 11ga pipe and set it in concrete.
Phased all-driven arrays are very hard to tune. I used 75 ohm RG59 for the phasing lines, feed the junction box with open wire parallel feeder, and you find variations in VF on lengths from the same roll of cable. And then you get it perfectly tuned, the temperature goes down, the Velocity Factor goes up and it's out of tune again. In February when we make our first set of attempts for the new year I'm sure I'll be out there in 20 below with the analyzer tuning up spacing on the elements to match the VF of the phasing lines at sub-zero temps.
And all that work for about one minute of glory that there's only about a 10% chance of being successful at.
The other station I'm working with that built the wireframe reflector, and I, are going to try simpler EME, station to station when the moon is a little higher in the sky. I can only tilt my array 30 degrees so even that has a pretty narrow window of opportunity.
But it's still fun, and a nice departure from working HF all the time.
When I go over to Steve's place sometime I'll take a photo of his wireframe reflector he built. It's pretty big, made mostly out of 2/4's for the framework to hold the dish movement. And he made the framwork for the dish itself out of light angle and 3/16" steel rod with several microwave screen reflectors laid in it. It's a pretty impressive antenna, made mostly of parts gotten from Menards, except for the microwave reflector screens which he got salvage off a microwave tower someplace. Took him all summer to build it.
Merry Christmas!
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