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Part Number: LMX2571
I am using LMX2571 in PLL mode using internal VCO for synthesising two VHF frequencies. As per the design I need to switch between these two frequencies alternatively in a specified time interval.
For this I have configured F1 and F2 registers for these two separate frequencies respectively and for switching between these two signals, both Trctrl mode and Reg control mode was tried.
By observing the direct output from LMX2571 i.e ( output of RFoutTx & RFoutRx) following result was obtained ;
1. When F1 and F2 was alternatively switched with TrCtrl mode / register select mode - spikes were present in the output spectrum.(snapshot of spectrum attached below)
2. When this F1 and F2 switching was disabled i.e either F1 or F2 is used - there were no spikes in the output spectrum.
Is there any way to remove the spikes from output spectrum for the above mentioned scenario?.
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In reply to Dean Banerjee:
Thank you for your prompt reply.
In the above mention issue the spikes are not fixed at certain frequencies rather they come and go at multiple frequencies on both sides of the centre frequency
*NOTE :This spikes are present only when Rx/Tx switching is enabled ( either by register mode or Trctrl mode).
I have attached a video of the scenario, i think this will explain the issue in detail.
In reply to Vishnujith KJ:
In reply to Noel Fung:
Thank you for your prompt reply. As you suggested I have connected the TrCtrl with Ext trigger of spectrum analyser with the following sweep time,( were Tx/Rx toggling time is 30ms)
1. sweep time - 30ms. when this sweep time was configured the spectrum was not visible . The attachment below will show the relevant observation.
2. sweep time - 80ms ( some portion of the spectrum was visible with spikes)
In addition I have measured Spectrum of another DMR Radio with the same Spectrum analyser settings as of case 2.( sweep time 80ms ). The attachment below shows the relevant details.
So even with the same Tx/Rx toggling time ( 30ms), with the same Spectrum analyzer settings the output from other DMR radio was fine.
Hope you will provide alternative solution for this spike issue due to switching of Rx/Tx of LMX2571.
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