Forum Replies Created
- Posts
Quadsat,
We do not specify relative amplitude accuracy, but as an FFT-based spectrum analyzer it is typically very good. After the device has warmed up for an hour, as long as you avoid switching bands which can add a tenth or two (dB) to the uncertainty, you should typically see a few hundredths of a dB relative amplitude accuracy until you approach DANL or the device changes temperature.
April 25, 2019 at 9:28 am in reply to: BB60C, EMC measurements:How to lower the noise floor of my setup ? Karlist,
With the BB60C, maximum sensitivity is achieved at 55 dBuV maximum input level, or -50 dBm maximum input level.
As far as measurements being 20 dB off… is the antenna the same distance as in your test site, or did you compensate readings for distance to DUT? Did you factor in any preamplifiers or cables used? Using a chamber without absorber will skew your results as well, but not by 20 dB… however, using a test distance of 3 meters instead of 30 meters would give you a 20 dB offset.Unfortunately, no. Due to the small pattern buffer, a test GPS signal cannot be generated.
With our VSG60A (coming later this year), you can play very long patterns. If you have software that generates a GPS test signal, the VSG60A could play it.Flo,
1) If I read that correctly, the gain of your amplifier is 1000 volts per amp. So I would think you would convert the SA44B noise measurement to volts per rt Hz, and then use this as your noise measurement (mA/rt Hz because amp output is 1V per mA input).
2) You are using power averaging, so there is not a 2.5 dB correction to apply.Also, please note that if your gain was 1000V / V, this is actually 60 dB of gain, not 30 dB. (20 dB gain = 100x power increase = 10x voltage gain)
Jared,
Because the SA series uses a software algorithm for image rejection, it is not a good candidate for EMC precompliance (except possibly for measuring fixed clock harmonics).We will be adding a preselector to the BB60D, which should be out later this year.
In the short run, assuming you are focused on accurate harmonic measurements, a high pass filter to remove the fundamental but pass the harmonics is a good solution. Mini Circuits has a collection of low cost SMA high pass filters.
The ENBW is going to be very close to the selected bandwidth. My guess would be at most a 5% difference, or maybe ~0.2 dB error.
Qswitch,
If you use “high dynamic range” scalar network analysis, the output power is both -10 dBm and -30 dBm in both cases. The damage level for the SA44B is +20 dBm regardless of attenuator setting (it could probably handle a bit more if the attenuator was set to 10-15 dB), but you can’t accurately measure signals above +10 dBm.
For passive high dynamic range, the pair of settings used is -30 dBm TG & -30 dBm SA (to 0 dB insertion loss), and -10 dBm TG & -50 dBm SA (for >40 dB insertion loss)
For “active” measurements, the SA reference level is moved up 20 dB I believe. The included 20 dB pad can be used to measure up to 40 dB of gain. To measure more gain than this, additional attenuation would be required.
If you are measuring an amplifier capable of more than +20 dBm output, I recommend using the 20 dB external attenuator. Or, more specifically, use enough attenuation so that if your amplifier saturates, it won’t blow the SA44B.You are correct that scalar network analysis units should be dB, not dBm, but our software’s control panel (at least when the manual was written) required you to enter a dBm reference level, and used this as dB. This may have been fixed since then.
marvistamike,
Do you have a torque wrench for tightening the SMA? Quite often, simply cleaning with a bit of isopropyl alcohol if needed and tightening (but not over-tightening) the SMA to ~7 inch-pounds can fix the problem. If not, we can set up an RMA for you.
I guess I should add that an isolation transformer could, in theory, work, but one that performs well down to 10 Hz might be very hard to find. As for an opto-isolator, my primary concerns would be linearity and noise, and you would likely still have to DC block.
Last time I needed to AC couple down to 10 Hz, I used a 220 uF aluminum polymer cap for DC blocking with a 1k to ground after, using two SMA connectors and a soldering iron. It wasn’t pretty, but it worked.
If your lowest frequency is 10 Hz, and your highest frequency is 100 kHz, and electrolytic will probably work fine. If you need to go up to a MHz or beyond, a polymer cap will work. For 10 Hz, you would be looking at something like 200 uF – 470 uF.
A 1 kohm resistor to ground after the cap will help discharge the cap AFTER powering on your device and BEFORE connecting the SA44B. A 50 ohm series resistor somewhere is desirable if you have a low impedance output.Hopefully this helps.
Maksym,
I and Q values are voltage rather than power, so you have to square them to get a power unit.Danz,
The Spike software allows you to configure the spur reject mode, as well as change RBW / span. Unfortunately, these are the only tools we have for the SA124B when it comes to spur mitigation.
You can look at the SM200A. If you require better spurious performance than the SA124B offers, this would be the next step. It is also much, much better at capturing periodic bursts of energy.
Jay,
No, I don’t think we have implemented this. You have to press Ctrl 1 thru Ctrl 9 to load a preset.The BB60C would be the minimum for this test (SM200A would be better). Zero span amplitude vs time and frequency vs time plots, probably with a decimation of 1 for pulse shape, and decimation of 8 to 64 for frequency measurements would be ideal (higher decimation would reduce the noise). You’re basically just looking at the phase change on each I/Q sample, converted to frequency.
Bittware,
I just wanted to jump in and ask if you had considered looking at the pulse in zero span mode with a video trigger? The SA44B won’t give you a great plot due to resolution and bandwidth limitations, but the BB60C would give you a great plot of your pulse’s amplitude over time.Iker,
Unfortunately, the VSG25A must be powered on after the computer is booted to work properly. You should be able to find a USB 2.0 hub that can be remotely powered down and back on. This may be the best workaround. I apologize for the inconvenience.Nolan,
The short answer is that the IF to I/Q data transition is a frequency shift to exactly match your requested center frequency, and amplitude corrections to remove ripple in the IF response. The I/Q data is typically easier to work with than the raw IF data, as phase information is a simple atan2 function, and power is simply I*I+Q*Q.Serpi,
Yes, we use an environmental chamber to test the units from -40 to +65 ambient for our correction data across temperature. Typically, the internal temperature runs around 8-9 C above ambient in the chamber, so the device corrections should be valid from about -32 to about +74 C internally reported temperature.I would add two resistors:
1) A 49.9 ohm series resistor for a 50 ohm output impedance
2) A 10k shunt resistor to ground after the DC blocking cap to bleed off residual DC.