We noticed the dang SR560 is injecting noise into our beatnote spectrum at high gain. I found a ZHL-3A low-noise RF amplifier and we've added it in after the transmission beatnote RFPD and in front of the new mixer (ZX05-1MHW-S+) in our PLL loop to amplify our beatnote with low noise.
Our beatnote is ~100MHz. Amplitude is 2 dBm. The noise figure of the RF amp at 100 MHz is ~5.5. RF amplifies the beatnote to 19 dBm (we attached a 10 dBm attenuator to avoid saturation of our mixer, which is rated to 23 dBm RF input).
Before adding in the RF amp, the PLL OLG UGF is ~25kHz. The SR560 gain is 20. The Marconi FM Devn is 10 kHz/V.
After adding the RF amp, I took the same spectra with the same PLL settings as before to get a direct comparison.
The plot shows the direct comparison. The pictures show the settings of the PLL.
Edit (awade) Thu Dec 7 21:23:50 2017: Put the actual part/model numbers. Links die after a time, you need to actually list the part otherwise it will be a mystery.