Below 30Mhz on LimeSDR Mini - Full of garbage

From my use of my LimeSDR Mini I have found that FM garbage is everywhere. Even when almost no FM stations are viable on the FM Broadcast band. (I have an FM Stop Filter and also they are bearly visable)

Yet there is still a ton of them from about 50 Mhz and lower.

Why does the LimeSDR Mini have such a bad signal imaging problem?

Use good hardware BPF (or LPF) with high attenuation above 30MHz. Also, try RX GFIR filters.

I have tried with an MFJ 30Mhz lowpass filter and it seems the LimeSDR Mini is pretty deaf. Compared to an rtlsdr with direct sampling?

Seems also that unlike the rtlsdr it required this filter to not see all the nosie.

Unlike RTLSDR LimeSDR has much wider receive bandwidth (30MHz-3.8GHz) and sample rate can go as high as 80MHz. It has built in Rx LPF (up to 60MHz) and 3xGFIR for additional filtering. Sometimes it is not enough! Because of very strong broadcast station with ERP in MW you will need BPF with high selectivity (low insertion loss) and high attenuation outside band.
HF part is a little different story: you can’t receive or send directly on HF frequencies before upconversion (for Rx) or downconversion (for Tx). For example: 20m band is upconverted using NCO (NCOfreq = Losc30MHz-Rx14MHz) with Rx LPF set to 40MHz (sample rate can be low as 1.536MHz).
Many people forget this LPF settings and as a final result you will have deaf receiver!

This is example how 20m band looks with BPF+GFIR set to 0.4MHz.

This image is without GFIR filtering. Notice big bump on the right side of the screen! It is from GSM signals in the 840MHz region because I don’t have enough attenuation above 30Mhz.

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Okay? Still disappointed in MyriadRF about that up converter stuff to. I was sold an SDR that only supports down to 30Mhz with a upconverter attached. Which is NOT what was advertised.

But atleast I know it works for anything up to 3ghz. (Which is sort of boring. I bought this for Ham Radio HF stuff mostly.)

“Upconverter” is feature inside LMS7002M, not additional hardware. It uses NCO for HF but NCO can be also used above 30MHz (for example set NCO to 10MHz, Tx center frequency to 154MHz and your Tx PA LPF will suppress LO leakage for 2m band). Ham radio is not massive market as 3G,4G and others multiRx-multiTx modulation scheme. SDR software is usually with many options which are not set automatically and can cause frustration sometimes.
Anyway, Mini is advertised as 10-3800MHz SDR Rx-Tx (in practice without modification input circuit can receive 40m band) not as HF (1.8-30MHz) and that is what works well. Take a look at:
Not bad for dipole antenna (4m high inside attic, oriented N-W).

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How are you getting to 7mhz for 40m? I can bearly get to 10Mhz with out having to push the sampling rate out of spec. (Annoyingly NCO is limited based off sampling rate)

Currently I’m using 1.536MHz sample rate which allows reception down to 30-(1.536*16)= 5.424MHz (1.536MHz because it can downsample very easy to 48KHz audio VAC sample rate, 16 is maximal decimation factor, 30MHz is on SXR page Rx center lowest frequency).

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Maybe I don’t understand the NCO correctly. Isn’t it the freq being feed into the mixer that makes up that up converter?

(page 3 and much more…)

I guess I am to use to how RF mixer stuff works as a physical device and how I can click 1 button with my other 3 SDRs and instantly get HF stuff (lower then 30mhz)

So I manged to get it working correctly but even with filters. (FM and AM broadcast blocking filters) The limesdr mini seems deaf compared to a rtlsdr with direct sampling. No matter how high I turn the gain I can’t get any of the signals I can see on my rtlsdr to show up. (They are FT8 signals some very strong.)

Any suggestions?

I am using a dipole that is tuned for 40m and I have check both 40m and 20m with both the limesdr min and rtlsdr and the lime can’t seem to hear a thing at all.

I have also adjusted all the filter settings I could find that SDR Angle gives me to work with and nothing.

Can you try with SDR# and LimeSDR plugin!

I have tried but the plugin always just crashes. (Using the build of SDR# that comes with it installed)

This is what happens after I set it to LimeSDR then click the configuration gear.

See the end of this message for details on invoking
just-in-time (JIT) debugging instead of this dialog box.

************** Exception Text **************
System.NullReferenceException: Object reference not set to an instance of an object.
at SDRSharp.LimeSDR.LimeSDRControllerDialog.LimeSDRControllerDialog_Activated(Object sender, EventArgs e)
at System.Windows.Forms.Form.OnActivated(EventArgs e)
at System.Windows.Forms.Form.set_Active(Boolean value)
at System.Windows.Forms.Form.WmActivate(Message& m)
at System.Windows.Forms.Form.WndProc(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)

When clicking play it says the source is not ready.

From where did you download SDR# and plugin? What is the version?

From the AirSpy Site.

The “Community Package with Plugins” and its version is v1.0.0.1732

And LimeSDR plugin?

It came pre-installed in the " Community Package with Plugins" version of SDR# no idea of its version.

Try from:
You can download and select 32 or 64 bit version. It was tested with 32bit SDR# 1672 (not sure is this correct number). Also not sure about 64 bit version number.

That worked. I can now see the LimeSdr Mini in SDR# (And it works, Tested with some FM signals from my vertical antenna.)

So how do I get to HF with this? Seems to not have a way to control the NCO.