Transmitted signal at 100MHz visible at 5700MHz

Hi all,

I plugged the TX of a Lime to the RX of a Blade, transmitted a 2MHz wide noise around 100MHz, and I could see it while receiving at 5700MHz. I put a band pass filter that greatly filters everything out of 5.6-6GHz and I could still see the signal at 5700MHz.

Any idea of why such a thing would happen?

I did that test because I noticed some powerful signal around 2450MHz would be visible around 5800MHz on the Blade. When using a signal generator to generate a CW at 100MHz, nothing was visible at 5700MHz.

You are over driving the BladeRF. I have a 20 db attenuator in the line and the BladeRF 5700 MHz signal does not disappear until the LimeMini transmit gain is below 40.

Thanks a lot for taking the time to test with your own BladeRF and LimeMini.

What seems weird is that I get this even when using a band pass filter centered around 5800MHz, which should attenuate by more than 60dB around 100MHz.

That sounds like compression in the Lime itself. If you lower the signal by 3dB, does the spur go down by 3dB, or by a larger amount like 6 or 9 dB - if so, the signal is not an actual signal, but is compression in the front-end of the Lime, and no filtering will remove it as it does not exist in the actual input; you will have to take the Lime out of compression by lowering the RF gain in the Lime or by attenuating the actual signal.

You may have not noticed, but when you over drive the BladeRF - it generates signals almost everywhere across the BladeRF’s frequency range. I used a fan of frequencies across the transmit bandwidth and the fan appeared almost everywhere across the frequency range - a single frequency would be easy to miss.