Hi Mike2459, well met again....are you sure you have given the right reference to Illllim?
The most effective method to get rid of noise, local noise, is to isolate the receiver's input from noise sources, normally picked up by the shield of the coaxial cable lead-in and / or the grounding system. You speak of an "isolation transformer" as if all antenna transformers were the same. Most of us go to Ebay, or to any one of tens of sites and buys an "antenna balun", sticks it in, hoping for the best and then cries with disappointment. We all have forgotten about solving problems with out own ideas and our own hands, while the point in Amateur Radio is just this: learn and learn more by doing things ourselves.
Getting away from philosophy and into the noise problem, you should first CLASSIFY your site/receiving system, following the method outlined in "Assessing Receiving system performance":
https://www.sdrplay.com/community/viewt ... f=5&t=3685
This will give you an idea of the size of your problem and of the noise level you are in and more, it will tell you if your main problem is LOCAL noise or not. The referenced thread is focused on HF operation. If you are interested in LW operation, then you should look at the parallel thread:
https://www.sdrplay.com/community/viewt ... f=7&t=4003
where at present I am uploading noise levels measured over a period of 20 days.
Once you have determined where you stand, you have seen that your problem is local noise and you have determined how constant or erratic your noise is, you should consider BUILDING a LOW CAPACITANCE isolation transformer. I say building because you cannot buy one and it is very easy, taking probably half an hour of your time. The essence is in the low capacitance between primary and secondary. This transformer is NOT FOR MATCHING, but for shorting & blocking noise, so that it does not reach the receiver. It does not matter if it is lossy, as long as it removes noise even if it has a few db's of insertion loss. For low capacitance the ferrite must be small, the wire diameter small and secondary must be on the other side of the core, as far away as possible from the primary winding.
Why low capacitance? In the transformer the low noise path must be inductive only, capacitance makes the noise jump right across and therefore you must get rid of as much capacitance as possible. If one transformer is not enough, you can use two in series, effectively halving the capacitance.
You just need a very common and easily located 7 mm. external diameter ferrite toroid core:
FOR HF RECEPTION
Toroid core: FT-37-43 (material type 43)
Ext. dia.: 0.375"
Internal dia.: 0.187"
PRIMARY = SECONDARY: 5 turns enamel copper wire 0.5/0.3 mm dia, for 1:1 / 50 Ohm Z ratio. Primary will be between center and shield of coax lead-in. Secondary between receiver's antenna socket center and common. Most probably you should not connect any ground to the RSP.
If you intend to use the HI Z input of the RSP2 (better choice) then alter turns ratio depending on your antenna impedance, keeping in mind that the HI Z = 1000 Ohm. For a 50 to 1000 Ohm you should use PRI=3 SEC=10, enamel copper wire 0.28 / 0.23 mm. I realise primary inductance is too low and secondary turns should be more, but this is the best compromise I could find.
FOR LW RECEPTION
The transformer above will still work, but you should experiment with a (very) few more turns to reduce loss or resort to a Type 73 material: ferrite core FT-37-73.
For the other (interference) problems in shortwave reception, the built-in MW & FM notch filters are a big help, as well as resorting to LOW IF mode to get rid of spurious & overload. Finally, remember that a long wire is a good antenna (the longer, the better) depending on the space you have on hand.
Hope this helps.