[G0HZU_JMR]

With my RF sig gens I find the best isolation is achieved if I exploit the attenuator hold/lock feature. It's often possible to get an extra 10dB isolation per sig gen for free using this method. It locks in an extra mechanical attenuation stage at the sig gen output and then I can turn up the internal level to compensate. This only works up to the limit of the ALC hold/lock system but it usually allows an extra 10dB of mechanical attenuation in the step attenuator. The ALC bandwidth can also be set to narrow instead of the usual tens of kHz of ALC bandwidth. This really minimises any artefacts generated by the ALC.

One of my sig gens has an electronic step attenuator rather than mechanical but it still seems to perform very well for stuff like this. To get the best isolation from the 6dB combiner I generally add a 10dB attenuator at the sum port of the combiner. This combiner typically has >46dB isolation across the HF and VHF bands if well terminated at the sum port.

I've got lots of other combiners here including a wideband resistive combiner that has about 19dB port isolation and 9.6dB through loss. This performs a bit better than the classic 6dB resistive splitter in terms of port isolation.