ON7UN Amateur Radio
 VE4MA Feed
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Today we tuned the VE4MA feed.

Procedure:Using a network analyzer, a commercial hybrid coupler and a test feed with H and V probes. First we checked the test feed, which is a short style VE4MA feed, with no scalar. We use a Narda hybrid coupler to make our test feed circular. First, the cables have been checked, to see a 90 difference in phase on the coupler.

The Horn Under Test ( HUT ) is connected to the network anayler, as well as the test horn. On the analyzer, we look for Return Loss, ( reflection ) and opposite circularity ( transmission ). I wanted to tune for minnimum signal, transmitting in RHCP and looking to the LHCP port of the test feed. After tweeking the probes of the HUT, and tuning the screws, i ended up with > 30 dB RL on both RX and TX port. Circularity has been checked, by connecting one linear port of the test feed. By turning the HUT, we found less than 1 dB change in amplitude, proving the circularity was OK. The signal received by the test horn was 2.6 dB less, when linear polarity was chosen.

Below some pictures of the feed. We constructed this feedhorn in Brass.

         ve4ma_feed_in_antenna.jpg (72849 bytes)        

 ve4ma_feed.jpg (104224 bytes) 

 ve4ma_measurement.jpg (96988 bytes)





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