Splitter/Combiner Performance at HF

Small signal splitter/combiners are available surplus for very low prices, but there are a bewildering number of model variations. Many of these units are rated for fairly high minimum frequencies, particularly if you're interested in using them on HF.

I've tested a handful of splitters and report their low frequency performance here. I used an HP 3585B spectrum analyzer with its built-in tracking generator for these measurements; the accuracy should be within .25 dB. In each case a 50 ohm load was on the unused port; generally, the isolation (output to output) goes to pieces if the input port is not terminated.

In each case, the insertion loss was 3.1 dB, plus or minus 0.2 dB, at either 100 kHz or 1 MHz. However, the port-to-port isolation varied greatly:

Model Number
Rated Min. Freq. Isolation
100 kHz
1 MHz
MCL ZFSC2-15 MHz 22.2533.1
MCL ZSC2-1B0.1 MHz 24.340.9
MCL ZFSC-2-210 MHz 9.621.6
MCL ZFSC-2-40.2 MHz 15.724.8
MCL ZFSC2-5-610 MHz 12.7521.9