2019-07-09

10GHz Horn Antennas and Update on the LNB RX Experiment.

I have a number of horn antennas.
I am well aware that horn antennas of these sizes for 10GHz are a compromise. Small size is used, sacrificing gain, as compared to dish antennas.
Today I found a horn antenna calculator , so I can see what I should expect of the different sizes.
The calculations are like this:

- The largest horn (145x115mm): 20dBi (WR75 WG)
- Two slightly smaller horns (120x115mm) 19dBi (WR75 WG)
- Two metallised plastic horns purchased new: 17dBi (WR90 WG). Same as specified by manufacturer
- a tiny horn with a (Gunn or detector?) diode in an integrated waveguide/horn : 10dBi

I should be able to find more horn antennas when I get access to the rest of the storage - if I have brought them home when I moved, that is.
The three larger horns were painted when I got them, so I hope the paint is not too lossy.
For the 3 larger horn antennas I need to make a coax to WR75 transition. The 2 standard 17dBi horns need WR90. It should be possible to use the WG transition from some ancient single polarization LNBs I have, or, in the first instance, maybe use the preamplifier in the LNB as a 10GHz preamplifier. Still, a modification is needed, and the noise figure is expected to be about 1.5dB. Not as good as it could be, but still in the acceptable range.

It looks like I may have to create a 10GHz antenna "test range" in my garden, so I can check the gain figures (efficiency of the antennas and coax-WG transitions). It is a good thing that I now have a set of 17dBi reference horn antennas, so I can get some relatively reliable gain indications. I know, a test field is not ideal in a garden, due to reflections etc, but it is better than nothing. Yes, coax to WG transitions needed there, too.
Initially I expect to use a HB100 as the signal generator, and test, if I can find log detector covering 10GHz. I am trying to make it simple. It may be possible to use an old (low gain) LNB for converting 10GHz and use log detector for a lower frequency. More tests to do.

Finally, a small update of the LNB receive experiment:
I looked up today to see that the direction of the horn is about 60deg. off the heading to the local beacon. Impressive that I still get a signal at 36km.
The beacon is essentially always audible, now and then with some short dips into the noise.

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