Accessories:External Filters

The Filters

1090 MHz 3 Pole Filter (with two N female connectors)
Technical data: passband attenuation: 0.5 dB -3 dB bandwidth: 13.5 MHz	Technical data: passband attenuation: 1.2 dB -3 dB bandwidth: 6.4 MHz

Why is there even a gain when inserting additional atttenuation?

When adding a external filter, we add attenuation and degrade the noise figure, but if at the same time the bandwidth becomes less, so less atmospheric noise passes through into the receiver. One can really see that the number of frames per second raises when the filter becomes inserted while the range increases a little bit.

Here is a calculator where you can enter noise figure and bandwidth of your system. You may edit the first two lines in below table in order to see the effect of an external filter. Video-Bandwidth and Sigma are best knowledge assumptions.

The original values as I claim are:

Mode-S Beast standalone: Noise Figure 2.0 dB, RF bandwidth 30 MHz Mode-S Beast with 3 pole filter: Noise Figure 2.5 dB, RF bandwidth 13.5 MHz (see measurements below) Mode-S Beast with 5 pole filter: to be confirmed with next build

TODO ADD CALCULATOR SCRIPT

This calculation was created by my friend Luis Cupido, CT1DMK. Thanks, Luis!

Measurements of the 3 Pole Filter

I measured the 3 pole filter shown above on my own Rohde&Schwarz FSEA30 (GIF grafics) as well as on a ZVRE Vector Network analyzer (photo screenshots). The passband attenuation of 0.5dB was measured with a R&S SMPC generator and a HP436 power meter in order to have a much better accuracy.


The 3 pole passband measured with R&S FSEA30


Filter Measurements with a R&S ZVR VNA	As an experiment, I also measured the S11 and S22 with my own FSEA30 and a directional coupler, and I got the same values as with the VNA with a very good reproduction