A project log for Radio Telescope

To build and use a DIY Radio Telescope

andre-powellAndre Powell 02/21/2021 at 19:370 Comments

Today's entry is related to seeing what I could see without any form of fancy pants Antenna, Horn etc.
The first thing was to look at how good the Low Noise Amplifiers (LNA) are.
H/T to James this is where I have first used the Vector Network Analyser. Put in very simplistic terms this tells you what your circuit or kit responds to a series of frequencies. For those with a greater knowledge it displays the transfer function in the frequency domain. There are other uses but let's just leave it at that for now.
Not the Calibration was done but as it's a first I could possibly done better but this is indicative at the moment.

As mentioned in the previous post I decided to buy two LNAs so decide to look at their response. For those suddenly whimpering YES I did put a DC Block in !
I am not too sure if you can add labels to images but the first two images are the response curves.
These are supposed to pass signals through at 1.42 GHz.

As you can see both have some ripple in the pass band. Chebycheff anyone ?
After this I though what would a small telescopic antenna extended to 21 cm be like ?
The reason being it's the simplest thing at hand so a good baseline.
Effectively flung out of the window and see what I could see.
Now back in Spectrum Analyser mode I scanned between 1.421 GHz and 1.427 GHz. Noise as you would expect so I turning on the averaging function. Noise being random should over a period time cancel itself out. However a constant level will stay. I tried an averaging of 900 and saw a tiny peak which appeared to stay. The other rather useful feature is the Water Fall Display, again this shows if something is disappearing and then reappearing, like noise.

The water fall seemed to show that this peak was steady. When averaged over 450 units it was still there.
Now as you can see there are lot of smaller little peaks and I don't know what they are but it's all over the range.

Next I took the LNA out of the circuit entirely and had a look. No peak but also a lots smoother.

All in all I think a productive afternoon and gives me a good baseline to see how things progress.