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Justin CrooksModeratorJustin Crooks August 20, 2015 at 9:43 am in reply to: Issue with SA44 + TG44 scalar network analyzer on low frequencies //php bbp_reply_id(); ?>
Ivan,
The actual value of the 20 dB pad is not important. It is measured and nulled as part of the store 20 dB procedure. We just need enough attenuation so we don’t overdrive the ADC when setting it to the high gain state. This is usually 12-16 dB minimum. A 30 dB pad would even work, but the readings would be noisier.
Justin CrooksModeratorJustin Crooks August 20, 2015 at 9:39 am in reply to: New USB-SA44B, Large Spurs in UHF Band //php bbp_reply_id(); ?>
The BB60C residual responses are specified to be below -106 dBm, are typically below -110 dBm (at -50 dBm ref level) and most of them go away when you turn “spur reject” on. Unfortunately, it is difficult to do much better at our price point, and impossible to eliminate spurious / residual responses entirely, at any price.
Justin CrooksModeratorJustin Crooks August 20, 2015 at 9:35 am in reply to: SA44 and frequency hopping signal //php bbp_reply_id(); ?>
Thank you for the suggestion. Our solution for frequency hopping spectrum analysis is the BB60C. It has hardware image rejection and very fast sweeps.
There are a number of solutions for frequency hoppers using the SA44B, but they are generally case-specific and do not work in the general case. If you can keep the hopping to a 20 MHz band, the SA44B can be used with image rejection off (disregard the image responses ~21.4 MHz away), or if the transmissions are long at each hop (>sweep time) you can keep image rejection on and analyze 40 MHz worth of spectrum.
Beyond this, the BB60C is required.
Justin CrooksModeratorJustin Crooks August 20, 2015 at 9:27 am in reply to: SA44B Generating Noise //php bbp_reply_id(); ?>
BBowar,
The USB-SA44B has higher LO feedthrough than other models we sell, and the LO is offset by only 10.7 MHz. You can minimize it by setting a reference level around -30 dBm (which will turn on the RF preamplifier), or manually turning gain to 1, preamplifier on, attenuator to 10 or 15 dB. This should reduce the LO feedthrough to around -60 dBm (typical).
Choosing a product like the BB60C will keep LO feedthrough below -80 dBm, and will keep the LO > 1.2 GHz away from the RF.
You can also add a circulator, ore even an external attenuator and/or preamp, to reduce LO feedthrough if needed.
Justin CrooksModeratorThe SA44B would work for measuring steady-state noise, such as from a clock, but intermittent noise would not measure accurately. The BB60C would be the recommended product for measuring intermittent / pulsed noise.
Justin CrooksModeratorJustin Crooks August 17, 2015 at 12:37 pm in reply to: New USB-SA44B, Large Spurs in UHF Band //php bbp_reply_id(); ?>
Ryan,
Unfortunately, spurs like this are normal for the USB-SA44B. The frequency is usually a little higher, but it depends on your cable lengths and computer. It looked like your spurs peaked around -100 dBm with a -30 dBm reference level for a 100 MHz span.When you use a span of 200 kHz or less, most of these spurs will be drastically reduced or eliminated. This is because the SA44B mixes differently for narrow spans.
Justin CrooksModeratorJustin Crooks August 12, 2015 at 9:09 am in reply to: Can't Lower RBW/VBW with some spans //php bbp_reply_id(); ?>
The best workaround is to show multiple captures. You could do several 200 kHz steps with low RBW. If you wanted you could export them as CSV, paste them together, and then plot using spreadsheet software or your favorite plotting tool.
I realize the RBW/span limitation at low frequencies seems odd, but the combination of hardware limitations at those frequencies, and the sweep performance we wanted for Spike, made it necessary.
Justin CrooksModeratorJustin Crooks August 5, 2015 at 9:37 am in reply to: How about the phase stability of two BB60Cs if an external freq. ref. were used? //php bbp_reply_id(); ?>
With a shared external frequency reference, in streaming mode only, there should be zero phase drift. However, every time you change center frequency, there will be a new phase offset.
If there is phase drift from floating point frequency correction rounding errors at some frequencies, I would think it would be very small and identical across devices and therefore cancel, but I have not tested this (maybe 1 degree per minute?).
At even multiples of 20 MHz (e.g. 200.00 MHz), this correction should be zero, so you should get a true zero phase drift. If you test this, let me know. If there is phase drift, there should be a way to easily get rid of it, possibly by using streaming IF instead of I/Q…
Justin CrooksModeratorJustin Crooks August 4, 2015 at 5:40 pm in reply to: Unit Conversion Equations, dBm/Hz //php bbp_reply_id(); ?>
The standard RBW works well for the BB60C, but not for the USB-SA44B. Because of the software-based image rejection, the default noise bandwidth is 2 x RBW, but then there is the software image reject algorithm. To get NBW close to 2 x RBW, you would need to either disable “spur reject” / image reject, or set video processing to power average and turn VBW down to 1/10 RBW.
To get noise BW close to RBW, you would need to filter out the image frequency. For wide sweeps, this is 21.4 MHz above or below the image frequency. For 200 kHz spans or less, this is 5.8 MHz above or 21.4 MHz above the measured signal. With image/spur reject on, filtering out either image will result in a good measurement.
Justin CrooksModeratorJustin Crooks July 30, 2015 at 10:30 am in reply to: Measuring 6dB bandwidth //php bbp_reply_id(); ?>
Another thing to note: For accurate power measurements, you need to keep the total power into the BB60C below +10 dBm. Your picture showed over +16 dBm. You will want to use a 10 or 20 dB pad for accurate measurements.
Justin CrooksModeratorJustin Crooks July 30, 2015 at 10:26 am in reply to: Measuring 6dB bandwidth //php bbp_reply_id(); ?>
For 6 dB bandwidth test, I believe the test is marker peak, then marker to the first point (left-to-right) less than 6 dB below peak, then delta, then last point (right-to-left) less than 6 dB below peak. You may wish to verify this, but I believe this is the 6 dB test.
Justin CrooksModeratorJustin Crooks June 26, 2015 at 9:36 am in reply to: Noise Bandwidth of Resolution Bandwidth Filter //php bbp_reply_id(); ?>
Bbowar, to simplify the thought process, we use wide flat top windows, so the noise bandwidth is very close to the resolution bandwidth.
Justin CrooksModeratorJustin Crooks June 22, 2015 at 10:31 am in reply to: Measuring DC power supply spectrum //php bbp_reply_id(); ?>
12V is not too bad, it’s people connecting to AC mains that can be really scary. An attenuator (or a limiter if sensitivity is important) is always a good idea though.
Justin CrooksModeratorJustin Crooks June 5, 2015 at 10:41 am in reply to: Labview drivers for SA44 //php bbp_reply_id(); ?>
Bbowar, you can also look at the simple, less functional Labview example in your C:\Program Files\Signal Hound\Spike\api\sa_series\labview folder. It doesn’t have all of the functionality of Lior’s program, but it might be easier to get running if you are experiencing difficulties.
Justin CrooksModeratorJared,
AJ pretty much summed up what you see. The center frequency gets set, then the frequency modulator (which offsets the center frequency) gets activated, then the modulation pattern begins looping.
I am looking at adding packet-based digital modulation with a 2-508 symbol packet followed by an “off” period of up to 65,000 symbols. This could easily give you a 1% duty cycle. Let me know if you are interested. The only (minor) challenge is I would have to convert FSK math from frequency modulation to its quadrature amplitude equivalent to enable this.
Justin CrooksModeratorWe could create a “packet” mode: send 2 – 508 symbols, then “off” for up to 65,000 symbols. Would this satisfy your requirement?
Justin CrooksModeratorAndy,
In Spike, you must explicitly set preamp AND gain before it will accept manual settings. With gain set to 1 or 2, you should notice a big change when you turn on the preamp.
Justin CrooksModeratorJustin Crooks May 11, 2015 at 1:46 pm in reply to: Labview drivers for SA44 //php bbp_reply_id(); ?>
KBONE, you can also download an evaluation copy of the latest LabView, save as a previous version (e.g. LV 2012), and then fix whatever errors creep in.
Justin CrooksModeratorJustin Crooks May 11, 2015 at 1:01 pm in reply to: Labview drivers for SA44 //php bbp_reply_id(); ?>
After unzipping, I had to create a sub-folder, “data”, and move shlv.ini into the folder. After that, it looked pretty good. Nice work!
Justin CrooksModeratorJustin Crooks May 11, 2015 at 10:08 am in reply to: Labview drivers for SA44 //php bbp_reply_id(); ?>
Excellent!!! I will try it out later today. Thank you for sharing this.
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