G8JNJ

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

Oh I quite like that idea.

Maybe it could be linked to the user defined memories in some way too, and then perhaps a scan function could be added, with either timed or squelch controlled pause / resume.

However, I think John has more than enough to deal with at the moment, so I'd just leave it in the "possibly nice to have" future enhancement category / pile.

Regards,

Martin

Ah OK...

Personally, I wouldn't recommend that model, but let's see how it works for you, when used with your antenna.

I'm not sure what device the Noolec is using, but I guess it will be something like the Qorvo QPA4363A.

Rather than issues with MW stations, it's more likely to be issues with possible overload from any strong FM broadcast stations, or other VHF transmitters that may be around your location.

The reasons I suggested a PGA-103 based amplifier for your application are, good IMD performance, low noise figure and rising input impedance, which helps improve signals on the LF bands, especially when using a short antenna. The current consumption is a bit higher at around 100mA. Noolec may have chosen a lower power consumption device, so that it can be used with the limited current available from sdr's with built-in bias tees, many of which have a maximum current rating of around 50mA.

But experimentation is all part of the hobby, so just try it, and be sure to report back with your findings.

If you need any specific help, send me a PM.

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

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

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

It's not that easy, as it depends on the source, and whatever it is connected to.

Especially as John has already indicated that there is likely to be more than one source.

That's why I suggest switching off your power at the main board, you will then be able to see what is under your control, and what is external.

Bringing the power back up, breaker by breaker, should allow you to better narrow down the location of a noise source.

Concentrate on one specific signal at a time, some of them will appear on many other frequencies.

Get rid of the worst offender first, and then gradually work on the others.

Be as methodical as possible.

Regards,

Martin

Most likely you will, so good hunting.

Oh and folks will soon be turning on their cheap Chinese made Christmas lights and decorations, so expect things to get worse for a month or so, until they get packed away again ready for next year.

Regards,

Martin