Products > Test Equipment

Video Teardown, Analysis and Repair of an Agilent E4407B ESA-E Spectrum Analyzer

<< < (5/9) > >>

electronic_eel:
Thanks for your videos, I really like the longer videos which go down into the details.

When you show the repaired SA with the PLL module in the last few minutes of the video with the full sweep (before zooming in on the freq of the pll), there is a large signal just at the left side of the display. What is that? Shouldn't the signal level be at the noise floor on the left side?

Hugoneus:

--- Quote from: electronic_eel on October 05, 2014, 07:19:21 pm ---Thanks for your videos, I really like the longer videos which go down into the details.

When you show the repaired SA with the PLL module in the last few minutes of the video with the full sweep (before zooming in on the freq of the pll), there is a large signal just at the left side of the display. What is that? Shouldn't the signal level be at the noise floor on the left side?

--- End quote ---

The PLL is unlocked and the instrument is trying to interpret various IF signals it receives from its several converters. I suspect that some DC offset signal from a mixer is wrongfully interpreted as a tone. Once the PLL is locked, this issue is resolved automatically.

HighVoltage:

--- Quote from: Hugoneus on October 05, 2014, 08:10:32 pm ---The PLL is unlocked and the instrument is trying to interpret various IF signals it receives from its several converters. I suspect that some DC offset signal from a mixer is wrongfully interpreted as a tone. Once the PLL is locked, this issue is resolved automatically.

--- End quote ---

Before I ask my question, I need to say, that I have not done much with RF, but find it fascination.
So, may be the answers are obvious to an RF specialist...

1)
I have an older HP Spectrum Analyzer Model 8596E.
This one also shows a peak at the very beginning of the sweep, when it starts the sweep at 9 kHz.
(Noting connected to the input)
Is it possible that this is inherent to HP spectrum analyzers?
I get a -1dBm at -100Hz
(see pictures)

2)
Why can I set my HP Spectrum Analyzer to start sweeping at a negative value?
i.e. -100 Hz

3)
And one more question, if you know the answer....
Why do most of these spectrum analyzers have a listed start frequency of 9kHz?
Why not 5kHz or 10 kHz or any other value?
Even some HP RF signal generators start at 9 kHz?
Was this an arbitrary selection by HP at the time or is there a significant technology reason behind this number?

Thanks for all your great videos.

Hugoneus:

--- Quote from: HighVoltage on October 06, 2014, 10:34:24 am ---
--- Quote from: Hugoneus on October 05, 2014, 08:10:32 pm ---The PLL is unlocked and the instrument is trying to interpret various IF signals it receives from its several converters. I suspect that some DC offset signal from a mixer is wrongfully interpreted as a tone. Once the PLL is locked, this issue is resolved automatically.

--- End quote ---

Before I ask my question, I need to say, that I have not done much with RF, but find it fascination.
So, may be the answers are obvious to an RF specialist...

1)
I have an older HP Spectrum Analyzer Model 8596E.
This one also shows a peak at the very beginning of the sweep, when it starts the sweep at 9 kHz.
(Noting connected to the input)
Is it possible that this is inherent to HP spectrum analyzers?
I get a -1dBm at -100Hz
(see pictures)

2)
Why can I set my HP Spectrum Analyzer to start sweeping at a negative value?
i.e. -100 Hz

3)
And one more question, if you know the answer....
Why do most of these spectrum analyzers have a listed start frequency of 9kHz?
Why not 5kHz or 10 kHz or any other value?
Even some HP RF signal generators start at 9 kHz?
Was this an arbitrary selection by HP at the time or is there a significant technology reason behind this number?

Thanks for all your great videos.

--- End quote ---

The signal you see below 9kHz is actually at DC. It is normal that spectrum analyzers show that signal especially the ones which are AC coupled at the input.

Spectrum analyzers (in normal sweep) will mirror the signals at 0Hz if you set the start frequency to a negative value. This features is useful when using external mixers or frequency offsets where the frequency axis can show relative negative frequencies.

The 9kHz value is the cut-off frequency of the internal DC blocking capacitor. This is a standard value. Making it less than 9kHz is very difficult while simultaneously meeting the higher bandwidth requirements. Very high performance spectrum analyzers are actually DC coupled and can measure down to 3Hz.

electronic_eel:

--- Quote from: Hugoneus on October 06, 2014, 02:34:02 pm ---Very high performance spectrum analyzers are actually DC coupled and can measure down to 3Hz.

--- End quote ---
But they usually have a big downside: you have to be very careful when measuring with such an instrument as the input stage will be destroyed if you input a dc signal.

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod