Mini 2.0 - RF Input Power limits

Projects LimeSDR
1

I have yet to find any clear documentation on the LimeSDR Mini 2.0 and the maximum power at the RF Input?
I have seen some extrapolations (including from Chat GPT) on the LMS7002 limits. but I really would rather have a manufacturer spec for the assembly.

What do you think the RF input max power is, and how did you arrive at that?

Thanks.

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I am not one of the developers/engineers who designed this board. But, we can deduce a few things by looking at the datasheets.

On the Mini v2.4, I see that J2 (the RX input) goes to a SKY13411-374LF chip whose absolute maximum input power is 32dBm.
Digikey shows a different interesting number for its isolation: 14dBm, whereas the datasheet says 23.5? Bizarre.
Regardless, you want your input power level to be lower than that isolation level.

Continuing to look at the schematic, I see that the RX path then goes into a TC1-1-13M-45+ RF transformer, which says it has an absolute maximum power of 0.25W (aka 24 dBm).

The RX path then goes into the LMS chip – I don’t see anything on the LMS7002 datasheet that explicitly tells you the chip’s maximum receive power. However, I do see that the wiki datasheet indicates that the receiver’s ip3db (3rd order input intercept) is 4 dBm, meaning that above 4 dBm of RX input power, you’ll see a large increase in nonlinear distortion caused by the chip’s own receive path.

Therefore, I’d have to conclude:

  1. Under no circumstance should you go above 24 dBm – above 24 dBm will burn out the RF transformer.
  2. You probably also should not go above 14 dBm, since that’ll violate the Skyworks chip’s isolation level.
  3. Going above 4dBm will result in nonlinear distortion of your signal, which might be OK depending on what you’re doing.

Honestly I’d advise you to stay below 0 dBm (1 mW), just to make sure you have sane thresholds for everything.

The board’s designers might have different advice. But until we hear from them… please be gentle with your input power level :smiley:

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