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My experience of building filters like this, is that the values provided by the various on-line calculators for self-supporting air spaced inductors wound from wire, is that they are not that accurate.

Even when you have wound them, and tweaked than so that their measured values are correct, you will need to adjust them again once they are installed in the circuit, in order to achieve the required response curve.

To do this you ideally you need a VNA, or Spectrum Analyser and noise source, so that you can bend the coils in real time and observe the effect.

SMD components can produce reasonably repeatable filters, as their construction and tolerances are much less affected by external factors.

However, if you don't have access to the test gear required to set it up, then there are plenty of cheap kits, or ready built, FM Band Stop filters being sold on AliExpress, starting at less than $5 USD, which is pretty much just the component cost if you were to buy the parts alone.

https://www.aliexpress.com/item/1005007644615468.html

Regards,

Martin

Regarding the DX Engineering RPA-2 pre-amplifier.

It's a good enough device, but somewhat expensive. I have used cloned copies of the RPA-1, which has a very good IMD performance, but the noise figure is not that brilliant, at around 6dB.

As your signal levels are quite low, I think one of the PGA-103 based pre-amplifiers that are available on AliEpress, such as this one, would be a good option.

https://www.aliexpress.com/item/1005005241002955.html

But you may need to add a 10dB attenuator on it's output, to bring the signal levels down to a more suitable average.

There are many other pre-amplifiers on AliExpress, that may work just as well or perhaps even better. But as most of the MMIC chips used in them only tend to be specified from about 500MHz upwards, I don't know how well they would perform on the short wave bands. From experience, the PGA-103 works well below 50MHz, and it's gradually rising input impedance, makes it suitable for use as an active antenna too.

Regards,

Martin

Thanks for doing that.

I think the Apex is better than the loop, but in both cases you seem to be constrained by local interference.

I can hear and see noise from several switching supplies, possibly solar PV optimisers, plus what I think is a domestic Data over Mains Powerline adaptor.

The sensitivity of the Apex falls off below about 5MHz, which is what I observed with my clone, but it should still be adequate in most cases, as the noise floor naturally rises on the lower frequencies.

Have you checked your own home for sources of electrical noise ?

Regards,

Martin

Those are valid, and he has identified himself.

It's a member of the UDXF list logging ALE networks, which requires long periods of continuous monitoring to capture stations that may only sound once an hour.

I have given him passwords for my KiWi's so that he doesn't time out.

Regards,

Martin

There was a long thread about the Apexradio 303WA-2 some time ago on this forum.

https://forum.kiwisdr.com/index.php?p=/discussion/comment/17853

The height of the antenna above ground is likely to have a significant effect on its performance.

Generally speaking, the higher you can mount it, the better it will perform.

Can you state your KiWi URL so that I can take a listen ?

Regards,

Martin