RX ANT Switching box,    part 2 - Preamp IP3

   There is my next blog post. It is focused to the IP and gain measurements of the single and double preamplifier. I use Motorola 2N5109 transistors and classic W7IUV design. As I described in my previous post , there are two splitted ones.

   

   I can switch off stage by the jumpers and sets bias for each transistor. It the table, you can see what happenes for the different biases and voltages. I measured output P1dB point (OP1d) and than calculated output IP3 (OIP3) :

 OIP3 = OP1d + 12  [dBm; dBm, dB]

   All measurements are done at 3500 kHz. I used R&S FSH6 + ATT + amp + ATT.

  You can see that double preamp IP3 is almost by 3dB better than the single transistor one. This responds the theory... Do not forget that there should be +- 1dB mistake :-) And IP3 is just calculated, not measured by 2-tone generator! But anyway you can obtain UFB results with this design. Do not forget, this preamp can easily exceedes 27 dBm (500mW) of the output power! This is quite a lot for the "normal" receiver :-)