I’m very curious to see the results and any conclusions.
Feel free to ask if anything needs clarification
Wow, 134 pages of goodness. Looking forward to quarantine
While scanning for my favourite SDR I found the following in section 2.2.6 on the USRP B210.
The wide bandwidth and frequency range make the BladeRF 2.0 micro an interestingchoice for satellite communications, both as a receiver and as a transmitter.
It seems the SDR name is wrong here.
Thanks, I have corrected it.
Amazingly useful report, thank you!! I haven’t read the entire report, but on page 21, you seem to measure spurious emissions by connecting the RTL-SDR to a 50 Ω load:
As we can see from the spectra, there are very few spurs generated by or picked up by the device when connected to 50 ohm terminator.
In this case, since the SDR is working in RX mode (and not TX), what is the point of using a 50 Ω load? Wouldn’t an Open or Short connector (from e.g. a VNA calibration kit) do?
The main point is to shield the antenna input from external signals while still having the receiver operate under nominal conditions, which includes a 50 ohm load at the input (might be 75 for RTL-SDR). Leaving it open but still shielded might work equally well, altohugh I have seen in the past that mismatched RX input can generate mix products in the receiver. I am unsure whether a short would work.
I think both load (of arbitrary impedance), open and short connected at the input port of the SDR will work, because your goal is to isolate the RX port from external RF signals. It doesn’t matter which one you plug into the RX port, because you’re not transmitting anything to expect any sort of signal reflections (where impedance mismatch and open vs short would matter).
(might be 75 for RTL-SDR)
Many old SDRs were rated at 75 Ω because they were intended for other applications (TV etc.). Now, almost every modern SDR (including the RTL-SDR) has an input impedance of 50 Ω. An easy way to tell is the connector: SMA connectors have a 50 Ω impedance, while F-type connectors (used for TV etc.) have a 75 Ω impedance.
(It would obviously not make a lot of sense to set a connector with a certain impedance and then have the rest of the electronics chain operate at a different impedance, so the connector is all the info you need in order to determine the SDR’s input impedance.)