It seems that the most popular front end amplifier in most dongles I have opened is the Skyworks 7150 series. This chip is seriously excellent with a gain of at least 18 dB at 1090 MHz, and a noise figure of not more than 0.5 dB at 1090!
Why is this important you ask? Glad you asked!
Here’s why: if you have the need to add an LNA to your setup, you WILL be degrading your system noise figure since NONE of the popular LNAs used with 1090 receive systems have noise figures approach this performance! Most have 1-2 dB NF, so remember that overall system noise figure is set at the first active stage.
For Reference, here is the product data in abridged and annotated form for you geeks. Notice that the device is optimized for 50 Ohm input impedance, and not as some have posted 75 Ohms, because the RTL chips are used in TV sets.
This is not to say you cannot use 75 Ohm CATV cable. As a rule of thumb, using a 75 Ohm cable adds about 0.2 dB max, in receive only applications.
I will be posting an SDR roundup that describes which amp chips are used in the popular 1090 dongles.
Message me if you have good eyesight and have data to include.
Full PDF Attached:
SKY67150_396LF_202922I.pdf (834.9 KB)