E M E - Station # 2


Some years ago I got an old 2m dish (f/D=0.6) consisting of 12 ribs and the center hub. I extended the ribs, resulting in a 2.8m dish with f/D=0.43, feed is a RA3AQ design.

The LNA is an old DD1XF cavity, based on the DJ9BV design and equipped with a MGF4919.

At the back of the dish I mounted a SSPA consisting of two PE1RKI amplifiers. So I have only 4m of Ecoflex15 coax and get 500W at the feed.

The results were quite o.k. for this antenna size, on the other hand I noticed that stations using an offset dish of about the same size have better performance in comparison, especially on receive, than stations using a 'normal' dish.

So after some calculations I extended the upper part of the dish to an effective diameter of 3m, and tilted the feed upwards by 25deg, of course leaving the phase center at the same place as before.

Sun noise with the new 'moderate offset' dish is 13.5dB (10cm flux 94), before the modification it was 11dB. Ground noise is 7.5dB (6dB before). Together with the calculated improvement of about 1dB on transmit, my own echos are 3...4dB better now, proved in reality.

When conditions are good (perigee, low libration), I can hear my own echos with 30W at the feed, and see the reflections on Spectran waterfall with 4W only.

I think that extending the upper part of the dish and tilting the feed could help stations using relatively small dishes to gain a couple of dB.

In the ARRL EME contest 2011 I was QRV on 23cm, random CW only, without any logger. It was very nice to receive with a SDR, after some time I learned how a CQ looks at the screen, and it helped me as well to find the weaker stations in the crowd. On one occasion I made a screenshot with more than 20 stations at the same time, see the picture beside.
Both parts together I worked 69 stations and identified 34 more call signs. So all together I heard 103, I think this is not bad for a 3m dish. I could have worked more, but some stations showed up only from time to time working some big guns and did not CQ themselves.

Stations worked in October:

Stations worked in November:

Stations heard only:
23cm ARRL 2011

The pictures show the dish before and after the modification, and how I mounted the SSPA at the back of the dish.

Listen to recorded 23cm own echos: 

3m dish 23cm echo 500W

3m dish 23cm echo 50W

Now the SSPA is mounted at my new 7.3m offset dish.

Instead I use a 80W SSPA with the 3m dish now.

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