Products > Test Equipment
looking for spectrum analyzer / network analyzer with 1MOhm Input Choice
David Hess:
High impedance buffer amplifiers are available to use oscilloscope probes with 50 ohm instruments.
https://www.mathews-engineering.com/store/p1/High_Impedance_Buffer_Amplifier.html
There are oscilloscopes which likely meet all of your requirements; I know LeCroy makes some. They can do network analysis because their FFT function returns the phase response instead of throwing it away.
https://www.edn.com/design/test-and-measurement/4441000/1/Measure-frequency-response-on-an-oscilloscope
http://www.testunlimited.com/pdf/an/55W_8815_2_2009.01.07.10.50.04_2765_EN.pdf
RFDUK:
Just for interest and to add to the vintage equipment list useful for this app ::) ....
TEK 7L5 was the HF spectrum analyser trend setter of 35 years ago, commonly used for down converted phase noise measurements. Has a 1M input option.
http://w140.com/tekwiki/wiki/7L5
Andree Henkel:
The 1M input amplifier is looking good; the R&S probe adapter is looking good as well. However most times they should be used with 10:1 probes, resulting in in my opinion unnescessary signal to noise ratio degradation. But in combination of the amplifier with the DC-Block I probably can also use R&S ZP1X 1:1 1M 38MHz probe; also prebiased photodiode + shunt would work in combination with that amplifier; still at 200€ for diode+shunt + 500€ for Preamp much cheaper than Femto TIA @2000€
Or with the R&S Probe adapter I could probably use R&S RT-ZPR20 power rail probe 1:1 50Kohm 2Ghz; less noise pickup by probe and low enough capacity + high enough input resistance for most in circuit measurements.
since there were no other suggestions we will have to decide:
a) "new" 50Ohm input analyzer; selection: R&S FSV4 10Hz-4GHz 18k€ new / 11k€ demonstration unit if available; +? FSV-B9: Tracking generator for FSV4 + 2k€ additional Femto TIA + 0,5k€ 1M Preamp
b) used HP3589A spectrum/network analyzer 10HZ-150MHz with 50Ohm/1Mohm; tracking generator included; about 4k€ with new calibration
I just requested prices from R&S for the FSV-B9 option, the Probe adapter and the powerrail probe.
The Powerrail probe I´ll likely try to get into budget anyway to work with the RTA4000.
We will not consider buying another scope from another vendor. We now have 2 Keysight, 1 Tektronix, 1 R&S scope in engineering, 1 R&S and a lot of yokogawas in manufacturing and we will not add Le Croy to this mix. Reason for this:
*each vendor is cooking its own soup with the proprietary probe interfaces, so each special probe we only can use on 1-2 scopes
*we have enough scopes around, what we need is spectrum analyzer / networkanalyzer capabilities without the possible Problems shown, we just want to make sure, we only see lines that really are there
*the 2 Keysight and the Tektronix have been around here for years. The yokogawa preference in manufacturing is based a lot on that special optical measurement equipment is bought from yokogawa.
*the RTA4000 was bought recently because it provides lowest noise level of the current R&S scopes and true 0.5mV/Div range setting; regarding FFT capabilities RTE or RTO would have been better choice but they are more noisy. We also had a 10Bit S Series of Keysight here for demo, but it was not as good regarding noise, but more expensive compared to the RTA. Maybe the 12 Bit Le Croy and the Tektronix 12Bit MSO6 are comparable with the RTA regarding noise.
joeqsmith:
The 3589A is getting up there in age. You should consider reliability and service if you are planning for the long term.
I have owned one for several years and had to pull it apart over the summer to do some maintenance. I use it a fair amount and over all it has been very reliable. Basic cleaning, had a connector come loose once, replace the battery has really been about it. Using LabVIEW with it is a snap.
I don't have the S-parameter set but have used it with an external coupler. There are some more options available when using the test set.
While it has the ability to select a 1M input, I seldom use it. Sometimes my projects get out of hand so normally I play it safe and buffer the input.
rhb:
The FFT "spurs" may be self noise of the DSO. I've been investigating that the last few days. Set the instrument to the minimum V/div setting, stick a 50 ohm terminator on the input and take a look at the FFT. Arguably a 1 Meg termination would be better, but I didn't have one.
Most of the scope makers seem to be unwilling to hire anyone who actually knows how to compute a proper FFT. GW Instek have a pretty good one in their spectrum analyzer app for the MDO, but the instruments have significant self noise and terrible shielding. The FFT in the other members of the GDS-2000E line is usable, but just barely.
The LeCroy DDA-125/LC684DLX FFT is also properly done, but not very flexible. But instrument self noise is much lower than the Instek.
I'm on an EMI witch hunt and finding that even a Keysight 33622A emits a ridiculous amount of noise from the LCD. I find this really weird as I can detect none from my computer monitors which are 15 years old.
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