To experiment with 2 receive antennas on the lower bands I needed some kind of splitter / combiner with some isolation between te ports. A google search brought the following webpage;
The fleamarket supplied the right torroids and it was quickly build. It proofed to be a nice design for the lower frequencies.
The result of my building efforts:
The unit open:
Measurement of attenuation to one of the ports. Up to 7 MHz it was more or less OK with a 4dB loss.
The isolation between the 2 ports is fine on the lower frequencies but is only 10dB on 20 MHz.
The same isolation measurement but now from 0-10 MHz
Isolation measured from 0-5 MHz
To see if the receive splitter would be OK on 138 kHz, a measurement from 0 – 2 MHz. The marker is on 140 kHz.
Yes the thing just works fine there!
Second attempt with splitter as published from the BCC. The article can be found HERE This is named CN8WW RX power splitter. It is considerable more wideband and it has a better isolation between the 2 ports.
Plots are from 0-50 MHz. 5 MHz per division horizontal, 10 dB vertical.
Top view of the splitter of the Bavarian Contest Club.
Plots are from 0-50 MHz. 5 MHz per division horizontal, 10 dB vertical. Losses are a bit higher but frequency range is very nice. Only one plot shown here but both ports were equal.
Measurement of the isolation between the output ports, input port terminated with 50 Ohms
The plot for the isolation: