After we had found out that the problem with our parabolic dish was that the feed probably was broken, we finally had an undeniably good enough excuse to open it and take a look inside. LA3WUA itched to pry open the can and discover the hidden wonders inside, and got to wield the heat gun.
Turns out the error in the feed was not very subtle or difficult to find. The antenna is not supposed to be heart shaped and misaligned, and it is not supposed to be bathed in a sea of moisture.
LA3WUA therefore went on to fix it.
Correctly aligned 23 cm antenna:
The next step was to avoid accumulation of condensation again by inserting a gore-tex plug into the feed, allowing moisture to go out of the feed box without any water entering.
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- Drilling a hole through the box.
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- Making screw threads for the plug.
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- Inserting the plug.
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- Waterproofing the sides of the plug.
We could then seal the box again …
… and re-insert the feed into the dish.
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- Hoisting down the mast.
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- LA3WUA inspects the coax cable.
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- LA1BFA uses his self-proclaimed good eyesight and good balance abilities to align the feed.
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- Installed feed.
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- Hoisting up the mast.
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- Vertical calibration of the rotor through use of LB6RH’s German alignment abilities.
We could then lean back and enjoy the view of the evening’s good work.
… until we discovered that the LNA also had stopped working, and we had to take everything down again.
LNA box.
LB6RH and LA3WUA took out the LNA, took a good look at it, tested it, found no error, reinserted it, and somehow made it work again. We will probably have to follow this up later.
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- LB6RH with a can of solo at the satellite station.
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- Spectrum from some of Inmarsat 3F2’s transmitters.
The full reception chain of the dish at 23 cm is apparently working again, and we could finally receive our first satellite with the dish (Inmarsat 3F2). Phew :-). We look forward to get on with the 1-10 GHz project.
Excellent work and very entertaining read! Are those four 50ohm terminators installed at the dish feed? What is their function?
Sorry for the late reply! The four plugs in https://www.la1k.no/wp-content/uploads/2018/04/IMG_20180409_201555.jpg are the connectors for the other bands that the dish feed supports (i.e. 13 cm, 9 cm, 6 cm, 3 cm, not necessarily in that order). The terminators are for weather-protection.
The corresponding antennas for each band can be seen in https://www.la1k.no/wp-content/uploads/2018/04/IMG_20180405_204755-1.jpg. The outer ring is the 23 cm antenna, which is the one that has been used in this blog post, and then 13 cm, etc. See also http://www.rfhamdesign.com/products/dish-feeds/multiband-dish-feed/index.php, under “5 BAND ring dish feed 23, 13, 9, 6 & 3 cm (1296, 2320, 3400, 5760 & 10368 MHz)”.
Nice to see the rise of the new generation of Adjustment Aces at LA1K.
Keep up the good work!
Hello ,
nice article. I was questionning myself abt why a friend of mine using this feed on 3cm was much weaker than normal? It was explaines by the pattern U measured , performance on 3cm is poor!
Abt 23cm , do U mean that the pattern U have measured in the anechoic chamber was with this damaged loop?
732
Dom/F6DRO
Thanks Dom 🙂
The pattern in https://www.la1k.no/2017/12/06/anechoic-measurements-of-rf-hamdesigns-5-band-ring-dish-feed/ was measured straight after receiving the antenna from the manufacturer, so it was not broken at that point.
73 Øyvind/LA3WUA
tnx , good information. I’m not satisfied by my 140cm dish performance on 23 using this feed , I will run sun noise measurements to see if it is only a feeling or not.
Your pattern measurements suggest the -10dB points aperture angle is too broad for good efficiency.
Tnx for very nice information agn
73
Dom