Direct conversion receiver (DCR), such as the LimeSDR or BladeRF, often suffer from har- monic mixing. Especially for low frequencies, where harmonics of the local oscillator (LO) convert unwanted signals into the baseband are a major problem for electromagnetic inter- ference (EMI) measurements. Performance measurements according to CISPR 16-1-1 would be violated by this principle. In addition to this, IQ-imbalances are also a problem in this context.
Because of the mentioned issues, an up-conversion stage which is capable of high dynamic ranges was designed. The board incorporates a filter bank centered at 1090 MHz with available bandwidths of 2-60 MHz.
As the investigated SDRs have sample-rates up to 60MHz it is possible to discard DCR technique and implement it as a heterodyne receiver.
In the following, the developed IF board has been characterized in terms of CISPR 16-1-1.