Sunday, May 13, 2018

ADS-B In-line amplifier experiments and bias T for 1 Ghz

By Easter was in Portugal and got an in-line satellite amplifier since it covers the ADS-B frequency of 1090Mhz
The idea was to put it in service for the ADS-B receiver, improving reception

Without any proper quality equipment to verify the effectiveness, decide do use the QSpectrum analiser software and record the data for comparative analyses.
In the process also trimmed the antenna to different lengths...
ending up in around 7cm (6.8 should be the calculated exact size).

Testing was done inside so subject to nearby interferences and yes, the support is a broom stick...

Here's the experiment and results:
 Testing with just the cable, no power and the amplifier inline:

 Powering the amplifier and no antenna:

Amplifier on without antenna and smoothing 100nF cap on the power line to the amplifier:
 Here with 1pF as DC blocking capacitor on the bias T:

 Now, opening the balcony door on the living room (where I was experimenting) changed results:

 Now still with the open door and a 10pF cap blocking DC:

I closed the door and experimented with a 120pF capacitor:

Testing the antenna ground plane:
7cm with GP:

7cm no grGP:

Ground plane helps :)

Different antenna sizes:



8cm (different scale since approaching the expected length)


In the final configuration it improved reception from my previous experiences, still the antenna being in house only get's a max of 60miles/100Km coverage.

The bias T for the amp ended up as a simple 180pF dc blocking capacitor (C1) one RF choke and a smoothing capacitor. The value was selected as a low capacitive reactance at 1Ghz and a little higher at lower frequencies:

@ 1000 Mhz

    1 pF - 159    Ohm
100 pF -     1.59 Ohm
180 pf -      0.88 Ohm
100 nF -         1.59 E-3 Ohm

@ 100 Mhz

100 nF - 1.59 E-2 Ohm
180 pF - 8.8 Ohm

The implementation and schematic:

Only missing now is to enclose everything and place it on the roof.

Have fun!

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