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| Agilent E4406A Vector Signal Analyser |
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| G0HZU:
I did some more testing on my E4406A yesterday and found something a bit odd... The front panel says the input is OK to 26V DC and this seems a very strange number. I did some testing and found that the input is not DC blocked on mine. So I decided to take the covers off to see what was inline at the front end. It seems to go directly into an SMA (7dB?) attenuator. But I did some more tests and there seems to be a DC block after the attenuator. I think this may be built into the attenuator back end. It can't be fitted 'backwards' in my case because the SMA connector gender at each end doesn't allow this. There appears to be a 7dB (SMA) attenuator at the input that is rated to several Watts. This doesn't seem to be rated to handle 26V DC even though it has cooling fins etc. Maybe the 26V DC spec is just for a short term application of DC. It's unlikely that my attenuator has 'lost' its DC blocking at the input and assuming that my E4406A is typical then it's worth noting that the input is resistive with about 80R shunt resistance. So be careful how you connect things to it if you assume it is DC blocked. Mine isn't! |
| KJDS:
I'd take a guess at the attenuator being about 5W. 26V into 80 ohms is 8.5W, so it's possible that it's capable of handling that, but as you suggest it's not a sensible thing to do for any length of time. |
| G0HZU:
--- Quote ---I'd take a guess at the attenuator being about 5W. --- End quote --- Yes, I'd say the attenuator type is rated/advertised for about 5W but probably to a spec with a few weasel words in the small print :) I think it's probably designed like this to withstand the RF power from a direct connection from a mobile handset. But mine appears to have a built in DC block at the other end of the SMA attenuator. This is inside the attenuator? Maybe this is there to protect the next stage in the RF front end from the attenuated DC from the max 26V fed at the input? |
| G0HZU:
While I had the covers off I had a closer look at the block diagram and the various coax cables between the modules. There is the ability to feed a signal directly into the digital IF at baseband if a cable is disconnected. The appeal here is that the system phase noise should be very low. Much lower than any of my mid range lab grade sig gens can achieve so they are useless as a test signal here. So I quickly tried a homemade 7.5MHz free running LC oscillator with a loaded Q of about 30. This should be capable of <<-150dBc/Hz at 10kHz offset. I tried this (via an anti alias LPF) in the E4406A and the E4406A limited out at -136dBc/Hz at maybe 3-10kHz offsets. Not bad! The idea would be to use an external LO and mixer to make a fairly decent phase noise measuring capability if a coax relay was fitted here. Note: My E4406A has the 14bit IF module which will help here. The external LO could be something like an AD9912 or AD9914 DDS that can deliver very low phase noise. This is still way off what something like a E5052A SSA can achieve in terms of phase noise floor but it's a big step up from a decent lab grade analyser in this respect. I also had to play inside the advanced FFT menus to get the last few dB of performance when so low down in signal level. The plot below is on 15dB/div not 10dB in order to get it on the screen. The Err logo on the screen is because the analyser is not happy that I broke the signal path to allow this signal to be fed into it. So it failed to complete its regular self test signal routine. |
| Neganur:
Actually a question regarding the 89600 software. I remember requesting a trial license to see how well it works with the 3000X series oscilloscope. Does the software need a license to run with the E4406A or is there a license on the device itself like on some infiniium oscilloscopes? |
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