So, what have I been playing with? Lots of
cheap stuff, naturally.
A newly acquired HP8562B, which I am using to explore the other stuff, and vice versa.
An old fleabay 4351 based synth:
- up to 4.4GHz
- USB powered, optional 5V via 0.1" headers
- eval kit software that runs in XP in VirtualBox in Xububtu
A newer TI LMX2594EVM eval kit that I picked up for £20 in an auction:
- 10MHz-15Ghz
- I'm only looking at one unbalanced outputs (two balanced outputs are available)
- onboard 100MHz source, or external balanced or unbalanced signal source - selectable by changing SMD resistors (hey, it is an eval board!)
- USB interface with another 100MHz differential output source, but a separate 3.3V 400mA PSU via an SMA connector (what else?)
- eval kit software only runs in Win7 or later. Changing frequency involves:
- changing a textbox embedded in the block diagram
- changing any other parameters that have "turned orange" because of inappropriate values
- forcing the 2594 to change frequency
So, what does the 2594 look like?
At 15GHz, no spurs visible, and noise level is set by the 8562:
At 4GHz, spurs at +-32kHz, noise is not limited by the 8562:
At 55MHz, also spurs at +-32GHz; is this in the source or the analyser?:
EDIT: see
https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg2471700/#msg2471700So what does the 4351 look like?
By comparison the 4351 looks dreadful at 4GHz, with lots of strong spurs which are sufficient to visibly degrade the stability:
But is that noise from the USB interface? What happens if the 4351 is powered from a bench PSU?
Much better at 4GHz and 55MHz:
Unsurprising moral: don't power a synth from USB power supply!