Sunday, November 30, 2014

Prj133 Mixer at 1575MHz IF (Part 2)

Given the issues with the high frequency balun, I populated the synthesizer and discrete balun for a 1575MHz IF output.  The schematic can be found in this post. The balun values used are shown below.
Component
Value
Comments
C105/C113
120nF
DC blocking capacitors
L102/L103
6.8nH
DC supply chokes
L107/L108
10nH
4:1 Lattice Balun inductor
C106/C107
1pF
4:1 Lattice Balun capacitor

The following is a picture of the final assembly:
Synthesizer (ADF4351 - left off center) and Mixer (LTC5510 - right center) using a 1575 MHz discrete balun (upper right).  Power and digital interface at left via 2x5 header.  
This was then used to sweep 200MHz about an IF of 1575MHz using various RF input frequencies.

The measurement device has an uncertainty of +/-2 dB.  The input RF level should remain fixed, however, its level can be pulled a dB or so with load reactance.  So the +/- dB wobble across the IF band is not a surprise.  The level falling off with increased frequency is also not a surprise given the board loss with the LO at 3.2GHz for the higher RF input cases. 

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