Hi Leo
This E5052A is quite old now and it does have a few internal spurious terms. Also the noise floor performance isn't that great even down at 10 MHz.
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I don't have any oscillators here that can generate really low phase noise close to carrier. A few years ago I designed a 10 MHz crystal oscillator with low phase noise but I think it only managed a noise floor of about -173dBc/Hz from 10 kHz onwards. This was the theoretical noise floor of the oscillator (at least according to my basic calculations) but I don't think I've ever seen -180dBc/Hz even with lots of correlation. I've never used more that 100 for the correlation setting though.
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I'm fairly certain the E5052A just uses an external reference to discipline the internal reference. Both of the E5052A analysers that I have used have an internal high stability OCXO mounted inside the chassis and this has its own output at the rear panel. The idea is to link it to the REF IN connector with a short BNC-BNC jumper and then it shows up as an external reference even though it is actually inside the chassis. My E5071B VNA uses a similar system for the OCXO option.
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If this BNC-BNC link is removed then the E5052A uses the main 10 MHz oscillator inside and the OCXO is ignored.
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The best thing about the E5052A is that it is very fast. What isn't so good is the qty of internal spurious terms, especially the one from the backlight at 60 kHz. I don't think it can compete with modern alternatives in terms of the noise floor it can achieve. The E5052B is going to be better I think. Hopefully the internal spurious are improved on the E5052B as well.
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The baseband input of the E5052A is normally locked out in software with no mention in the documents how to unlock it. I think Agilent decided to hide this feature, probably because of the internal spurious that spoil the performance and also the noise floor rises a fair bit at low frequencies. There is also an enhanced jitter option which I've played with but I don't have much need for stuff like that. The jitter option is documented and available but the baseband isn't. I had to hack inside the firmware of this E5052A to find out how to release the baseband option. It can't be done via the option menus in the way the jitter option can be unlocked.
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If you look on Eevblog, I'm currently testing one of your LBE-1421 GPSDOs.? I'm getting the same result for phase noise that you did. I'm G0HZU on Eevblog.
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Regards
Jeremy
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