Monday, 21 December 2015

Some low noise tests

Merry Christmas,
I had intended to work on my EME dish today. However, the weather has been very wet and windy since mid morning. Consequently I decided to do some measurements on the LNA with a view to reducing my EME system noise temperature on 23cm.

After (re)reading a number of interesting articles on noise figure reduction by SM5BSZ and RW3BP I thought that I would measure the insertion loss of my LNA protection relays. These are SMA types by one of a number of manufacturers and all are surplus ( second user) SMA types with 3  in-line SMA female connectors. All are12V working.

After carefully calibrating my HP8753C network analyser ( warmed up for several hours) i found that the best I could do was 0.071dB insrtion loss from a Totsoel with 0.1dB from a Teledyne CCR 33S80
I must stress these are used relays. I have to use what I have!

The net result of using the Totsoel relay with an SMA90 bend to the feed and SMA male back to back adapter between the relay and VLNA is 0.38dB as a noise figure.
This is quite good but I believe I can improve on it using some of the techniques describd by RW3BP.
The back to back adapter can either be eliminated completely or replaced with a modified version using a piece of UT141. The probe to relay connection can be made in one piece to eliminate yet another SMA connector.
Now to try a few of thse ideas.

Sam


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