We're using a HMC558LC3B in an up-converter application and seeing, frankly, horrendous LO+2IF spurs.
IF = 950MHz, LO 9750MHz, RF 10,700MHz spur is at 11,650MHz and only -20 to -25dBc. Our spec is -50dBc, so as you might imagine, we are up the creek...
Input drive level is about -6dBm, so well backed-off.
The IF amplifier is 20dB backed off from compression at this level so the harmonic level into the IF port should be negligible. We've replaced the mixer with a fresh device (my initial thoughts were that static damage has blown one half of the diode/FET pairs and the balance was upset) but only seen an improvement of 3-5dB. (Consequently, the 2LO-RF improved 10dB - so are the mixers very sensitive to process variation? Do the MxN spurs vary this much, device to device?)
Q1. Is this performance typical of this device if used in an up-converter application?
If not then...
Q2. What are the potential causes of high LO+2IF spurs, apart from high levels of 2IF entering the mixer in the first place?
- input match?
- LO drive sin or square? We are somewhere in the middle, aiming for P1dB of the LO driver amp.
- Something else?
Thanks in advance.