The lengths of the striplines also affect the phase of each signal at the output ports of the divider with longer traces in some paths causing more phase change in those paths. You don't usually see 50 ohm striplines going to individual attenuators at each output in a power divider.

This arrangement provides good isolation between ports and requires only one attenuator at the divider input for gain adjustment. 4-way and 8-way would have progressively higher impedance stripline traces. For example a two way divider would have two stripline traces that are roughly 75 ohms each and 1/4 wavelength long each then bridged at the output side with a 100 ohm resistor. This is because they are usually a Wilkinson power divider and the traces are a specific length in fractions of a wavelength and not 50 ohms. I saw some questions on the github site and one was about symmetry in the PCB splitter legs. Excessive gain can push the amplifier into IMD land earlier for no good reason. Have you considered a higher IP1/IP3 amplifier? Its also better to choose an amplifier with just enough gain to overcome splitter losses which should be around 6-7dB for a 4-way and 9-10dB for an 8-way. Those are specs at 5V and they are worse at 3V. I see the amplifier chosen has an IP1 of less than 20dBm and IP3 around 33dBm, both pretty low and can contribute to overloading in many users areas due to high RF environments. Do you have any slope compensation for the amplifier that has 7dB more gain than at 1GHz? Maybe replace C1 with something in the 2-4pf range which will roll off low frequency gain? I have a few questions after looking over the schematic. If anyone is interested in participating in a bulk purchase, let me know what you'd be interested in: I think I could get that down to $10 or $15 buying parts in larger quantities. I just got the first prototype PCB assembled today and it seems to be performing about as expected, but I haven't taken any measurements with real test equipment yet.Ĭost to build a single prototype was about $35 for parts, circuit boards, and shipping. The SMA males connecting directly to the SDRs can easily be substituted with SMA females if cable connections are desired instead.ĭesign files and more details are here if anyone wants to make their own. It can get power from one of the RTL-SDRs equipped with an internal bias tee or from external regulated 3 to 5 VDC. The intended use case is to feed a bank of four RTL-SDR dongles plugged into a USB hub with a single antenna, but it can be used for other purposes as well. Here's a 4-port active multicoupler that I put together.

Bias amp 2 stereo