5.8 GHz Helical Feed for the 90cm dish

Yesterday was day 2 where we were repairing the broken Azimuth rotator and making a small 90cm dish ready to track UNITEC-1 on 5.84 GHz. Actually, we already fixed the rotator on Monday but we ended up mounting it 180° off and we decided to fix it properly instead of just correcting it in software.

Fixing the orientation of the Azimuth rotoator was very quick – it took only 17 minutes to get up to the mast, lift the antenna construction, change the orientation of the rotator and fasten the nuts and bolts again. We had the practice from yesterday.

Next item on the agenda was to make a small helix with two turns to feed the 90cm dish so that we can use this smaller dish for tracking UNITEC-1 in the beginning of the interplanetary cruise. We found some online helical antenna calculator to generate the design but that was more than 1 GHz off and it took a lot of tweaking and tuning to get it close to 5.8 GHz. Here are the results, photos and videos.

The finished helical feed:

5.8 GHz helical feed

OZ2ABA mounting the helical feed and LNC on the 90cm dish:

OZ2ABA mounting the helical feed on the dish

The helical feed and the Kuhne KU LNC 5659 C PRO downconverter mounted on the dish:

The 5.8 GHz helical feed and the Kuhne LNC moutned on the dish

USRP, WBX and GNU Radio in the shack receiving OZ7IGY!

Test setup with USRP, WBX and GNU Radio

Here is a recording of OZ7IGY beacon on 5.7 GHz.


A summary of the results from repairing the Azimuth rotator and making the 90cm dish work on 5.84 GHz:

  • Azimuth seems accurate within 1° – calibrated against TV transmitter mast with well known coordinates and OZ7IGY on VHF, UHF, and 5.7 GHz.
  • Elevation might be a few degrees off
  • Manual steering is very difficult on 5.8 GHz – you touch the knob and it moves 3° which is too much on 5.84 GHz with a 90cm dish.


We are hoping for successful launch of UNITEC-1 on Thursday!

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Author: Alexandru Csete

Embedded software engineer in the satcom industry during the day. Radio amateur and SDR hacker during the night.