Low noise pre-amplifier for ADS-B reception

Two weeks ago, my son asked me to donate him the RTL SDR and the old antenna for ADS-B, to join FR24 network. I said yes, and I re-install the antenna, unfortunely not so high as needed, not with proper coaxial, etc. After 30 minutes the set-up was ready. After few days, I checked the results and I found the maximum range 115 nm and only 600 aircrafts seen daily. I said is normal for an antenna obstructed and 10 meters RG58 cable (let say, 6 dB losses, at 1090 Mhz).

On the other hand, I stopped any hamradio QSO, because I was afraid to not destroy the SDR, without a proper filter (the distance between my delta loop and 1090 antenna is about 4 meters).

So, I passed to next step, building a cavity resonator and finding a good pre-amplifier. For the moment I am not very hapy with the filter I have build, but I shall let you know later… after I shall can tell you what not to do when you build a filter !!!

I found in my junk box an old antenna (with the housing broken) with an GPS antenna and a pre-amplifier inside.

The amplifier is build with 2 transistor, the 1st is a sms marked V80. I found the datasheets, is a NE3509M04, Ga-As transistor, NF=0.4dB, Ga=17.5dB. The total gain of the module it seems to be up to 25 dB.

Now, the order of operation.

Remove the shield and the ceramic antenna

Remove the filter and coaxial cable used for output (it was cutted and too short)

Solder a capacitor to replace the filter and connect 1st stage to the 2nd stage of amplifier. If you dont have a very small capacitor (as dimension), somewhere between 1-5,6 pF, you can use twisted wires.

For connecting the signal to input, you shall find very easy the pads on the other side of the pcb. In the middle is the center of the coaxial, the rest is ground.

Solder the coaxial to input, output, solder back the shield, build a 3 – 5 Vcc stabilizer, connect the antenna through a filter (this will be another story), and conect to the SDR.

The practical improvements of reception: increasing the reception range from 115 nm to 145 nm, increasing the no of aircraft seen from aprox 600 daily to 750 daily, from maximum 50 reports daily from more than 100 nm, to minimum 1200 reports daily from more than 100 nm.

As I said, about cavity filter, next time. I didnt have enough time to make all the possibil mistakes !!! (what is running now, it looks like a cavity, but only looks).



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