Total posts : 45366
Try Rich’s suggestion but if there is some diode action nearby this may not help but you should see some change. Your receiver has an attenuator built in and the purpose of this is to reduce overload interference. Do you notice any change if you switch it in and out?
When I was designing a transmitter I needed a 7 pole low pass filter but I don’t recall how I designed it. I think I used some sort of program for this but I do remember I simulated it with LTSpice. You will need a high pass filter which is just a matter of exchanging the Ls and Cs and picking the right corner frequency. I’ll dig out my notes on this and post back if there is anything that looks to be helpful for you.
It could be that all you need is a simple low Q series LC trap as you mentioned and what I mentioned above could be overkill. The problem with using power supply toroids is the core material may not work at RF. Another problem is not knowing the inductance unless you have some way to measure this but it could be done trial and error and may be worth a try since you have the parts available.