I am using HMC431LP4, my Vcc is 3V and Vtune 4V for 5.8GhZ. Currently I am using voltage probe to measure Voltage output from the VCO. I am reading 1mV insread of 58mV, Do I need to use sma CONNECTOR TO GET DESIRED READING?
At microwave frequencies good grounding and short, shielded connections are important for accurate measurements. You're voltmeter with it's high impedance isn't going to be able to make a good measurement. If using the evaluation board you should use the SMA on RFout and a spectrum analyzer to view the signal and any harmonics. A power meter will also provide a good estimate of the nominal output power as long as the harmonics are decent, which they are on the HMC431. Of course be sure the current of the HMC431 is about 27mA prior to starting this process. If it's on your board it's a little more difficult especially if the VCO is part of a larger system you don't have an SMA connector to mate to at RF out. You can make an RF probe from a piece of 50 ohm, semi-rigid cable and an SMA connector and attach this to a good RF cable and use the Spec An, again due to less than ideal grounding (even if you add a ground lead) the output power will measure lower than actual.
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