LA1K / LA1ARK / LA1UKA

Satellite dish measurements pt. 3: Fixing a broken RF Hamdesign five band ring dish feed

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.

We could then seal the box again …

… and re-insert the feed into the dish.

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.

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.

6 Comments

  1. LA1WUA

    Excellent work and very entertaining read! Are those four 50ohm terminators installed at the dish feed? What is their function?

  2. OH3BK

    Nice to see the rise of the new generation of Adjustment Aces at LA1K.

    Keep up the good work!

  3. Dom F6DRO

    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

    • LA3WUA

      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

      • Dom F6DRO

        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

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