RSP2 interference

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dtyndall
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Joined: Mon Mar 12, 2018 6:15 pm

RSP2 interference

Post by dtyndall » Mon Mar 12, 2018 6:18 pm

I have a spike in the middle of my RF passband no matter where I tune. This is present with the antenna connected or not. Any suggestions?
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Tech_Support
Posts: 499
Joined: Mon Jun 01, 2015 7:00 pm

Re: RSP2 interference

Post by Tech_Support » Mon Mar 12, 2018 6:42 pm

What you describe is an artefact of the zero IF or direct conversion receiver. It occurs as a result of two mechanisms. This first is leakage of the LO into the RF path and self mixing to create a product at DC in the analog I/Q paths. The second is DC offsets in the analog stages of the I/Q paths themselves. All receivers that utilize this architecture will exhibit the same effect and some people refer to it as a DC spike. It will always be at the centre of the spectrum when viewed at the maximum span. Software is used to reduce the impact of this spur, but to be clear, it does this by applying a notch filter to the response. In that regard, it masks rather than removes the problem as the software is incapable of distinguishing between a real signal and the 'DC spike'. We always recommend that you create an offset between the LO and any signal of interest to avoid interactions with the notch filter.
As an alternative, the RSPs can also employ a low IF architecture, which removes the problem completely. However, in low IF mode, the maximum visible spectrum is around 2 MHz, but in this mode, there will be no DC centre spike.
You don't say which software that you are using, but in SDRuno, band framing is only currently supported in Zero IF mode. This is something that we plan to change in the future as we intend to support band framing in Low IF mode in a later version of SDRuno.

Sincerely

SDRplay Tech_Support

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dtyndall
Posts: 2
Joined: Mon Mar 12, 2018 6:15 pm

Re: RSP2 interference

Post by dtyndall » Mon Mar 12, 2018 6:45 pm

I am using HDSDR with the RSP2 as a panadapter on the IF out of my conventional radio. How would I go about creating this offset?
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Tech_Support
Posts: 499
Joined: Mon Jun 01, 2015 7:00 pm

Re: RSP2 interference

Post by Tech_Support » Mon Mar 12, 2018 7:50 pm

Open up the ExtIO hardware control window. then under the IF Amplifier section, select Low IF as the mode instead of Zero IF. You can then pick an IF bandwidth of up to 1.536 MHz.

Sincerely

SDRplay Tech_Support

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