Hi James,
Whether these units work depends a lot on the antenna you use as the “noise antenna”. What the unit does is to “phase” the signals from the two antennas so that the noise coming in on one port suppresses just that same noise component coming in on the other antenna. So your noise antenna needs to pick up the interference at a reasonable strength and then you “match” that against the main antenna and adjust it’s (amplified) level up to that of the interference on the main antenna. In theory all that is then left on the main antenna is the signals without the noise flattening them. Of course when you move frequency, you may need to retune the unit.
To set this up correctly is difficult and there are other downsides - these are great for SWLs but if you want to transmit, you need to make sure you don’t transmit through this unit - in fact it’s best to use on rigs with a separate receive antenna input.
Now if someone could come up with an Arduino (or other micro controller) based automatic tuning system for these devices, they could become very useful. But until then, mine is also sitting at the other side of the shack disconnected.
73 Ed.