I am using the HMC833 PLL+VCO as the LO source to a mixer for tuning to certain frequencies between 1GHz and 6 GHz. I noticed that the tuning frequency is usually off by several hundreds of KHz, which does not make it suitable for the finer tuning I seek in my project.
This offset depends on the center frequency that I choose, but is consistent for every frequency (after powering the device off then on). I am currently using the Eval Board along with Hittite Evaluation software to tune to a certain frequency, and this effect is present in integer and fractional modes.
I am using a spectrum analyzer to measure the frequency value produced by the PLL.
For instance, if I use Integer mode and tune the PLL to 2400 MHz, the spectrum analyzer shows the pulse at 2.399516 which is 484 KHz away from what I want. If I tune to 1000 MHz, I read 999.80 MHz on the spectrum analyzer, which is 200 KHz off. When tuning to 5 GHz, I read 4.998995 GHz, which is over 1 MHz off! Typically, I would expect a certain drift of tens of ppm, but this about 200 ppm for all cases.
I would like if this is expected in the normal operation of the HMC833 PLL+VCO, and, if not, to know what kind of modifications I could do to improve this, or at least what could be causing this.