On Mon, Feb 24, 2020 at 10:39 AM Heikki Laamanen <heikki.laama...@dlc.fi> wrote:
> Hi experts in SDR RF transceivers, > > > > I am working on a timing and synchronization system which generates a > high-precision timing signal from a terrestrial broadcast signal. I am > looking for a suitable SDR HW-board providing independent clocks for the RF > mixers and the ADC. > > > > It seems that many SDR boards use transceiver chips having mixer and ADC > clocks which are derived from a single clock. Thus, it is not feasible to > control the ADC sampling clock frequency without affecting the mixer > frequency. For example, some USRP products have Analog Devices AD9361 > transceiver chips providing no option to have fully independent mixer and > ADC clocks. > Is this assertion true? According to this document: https://ez.analog.com/wide-band-rf-transceivers/design-support/w/documents/10064/ad936x-local-oscillator-lo There exists 3 VCO's in the AD9361. One for TX, one for RX, and one for the baseband. Why do you believe the clocks are not independent? I agree the sampling clock might not be able to achieve the resolution you want, but I don't see why they are not fully independent already. > > > Why would I like to have independent mixer and ADC sampling clock? > > > > The target is to generate a physical clock signal having small jitter and > accurate phase. Hence, I need to control the frequency of some VCO based on > the information the receiver signal processing gives. The most > straightforward way to do this is to control the frequency of a VCO > wherefrom the ADC sampling clock is derived. > You need to be more specific regarding your jitter and phase requirements. Also remember that time is all completely relative. Lastly, what does accurate phase mean to you? Brian
