In saConfigSweepCoupling, there is a parameter that gets passed in, bool reject. If you set this to true, and decrease your VBW to maybe 1/10 of your RBW, you should get the expected noise reading and shape.
The reason for this is the USB-SA44B does not have hardware image rejection, and instead relies on a software algorithm. When this is not enabled, an image response shows up 21.4 MHz away from the actual input signal.
For broadband signal applications, the BB60C would be an ideal choice, since it has excellent hardware image rejection. But the SA44B can be configured to work well for signals up to 20 MHz wide, using the image reject flag appropriately.
Generally, if the signal is continuous, the image reject flag should be true. If the signal is pulsed or frequency hopping, you must set the flag to false to catch the signal, and the image response is unavoidable on the SA44B.
Hopefully this helps.

Your VBW was less than RBW, so you were low pass filtering the power response. Did you try setting VBW to auto, or = RBW?

I don’t think we ever made an Allan Deviation tool. The closest we have is the frequency difference meter, where you can watch the frequency error drift over time.

And when you change the detector to min/max, ensuring spur reject off, you see no change at all in Spike?

Mikeh,
Have you tried attenuating the signal to maybe -10 dBm (well into linear region of SA-series), ensuring detector is min/max, spur reject is off, gaussian filter. What kind of reading do you get?

The last picture had detector set to average. I’m just trying to figure out what the difference may be.

Generally, customers have reported that this works, but there has been some additional troubleshooting from time to time.

The frequency difference meter would be good for CW signals. I don’t know how it’ll perform with 4FSK. You might try our modulation analyzer in zero span for that. I think I’ve seen around 1 Hz typical error on readings there with time bases locked.
For a CW, using the frequency difference meter, a typical accuracy would be 0.01 ppb plus time base error, so in your case, +/- 1.01 ppb. At 440 MHz, +/- 0.4444 Hz.
Adding modulation complicates things a lot.

The actual frequency error for sweeping is (reference error + 1 sample), so if you have a sweep with a “bin size” of 10 Hz (around 40 Hz RBW), and a 1 ppb timebase, your marker should read within 10.44 Hz of the actual frequency.
You can calculate bin size as (span / number of points).
If you are using the frequency difference meter or the modulation analysis tool center frequency on a CW, the frequency error should be very small, as long as your signal to noise level is good. With the frequency difference meter, I typically see something like 0.01 ppb error.

Dragan,
1. I believe AUTO RBW/VBW is a function of Spike. If you like the RBW that Spike selects for your measurement, simply use this RBW, and set VBW = RBW.
2. In the same saConfigSweepCoupling function where you set RBW, set Reject = true for spurious reject
3. saConfigAcquisition is where you select average or min/max

The BB60C has a lot of advantages: sweep speed, signal purity, instantaneous bandwidth, etc. But the SA124B is perfectly capable of making good measurements on many types of signals above 6 GHz. Crowded spectrum, signals wider than 40 MHz, or intermittent signals are difficult or impossible to measure with the SA124B.

You could downconvert to any convenient frequency, but there are a lot of off-the-shelf converters for satellite systems that target 1-2 GHz IF, and a lot of mixers that don’t allow an IF much higher than this.

There is a DC blocking capacitor, so you should be fine up to 16 volts DC.

You can use a signal generator and mixer to downconvert to 1-2 GHz and feed into the BB60C. The mixer will drop amplitude 6-8 dB typically

Chuck,
If you are unsure of the output impedance, one solution is to add a low noise buffer (op amp), with a 50 ohm series output resistor and large DC blocking capacitor (passing 600 Hz would require about 22 uF to minimize impact on amplitude accuracy). You could also add some gain here depending on the expected signal level.

If this is not an option, you could try measuring the output impedance, or alternately see how much the amplitude changes when you add a e.g. 100 ohm series resistor to your output, and then use standard resistor divider equations to solve for output impedance (assuming a 50 ohm input impedance).

The goal of VBW > RBW is essentially to remove any significant filtering after the RBW. Our software is a little different in that we bypass VBW processing unless VBW < RBW or the average detector is used. So for Spike software, VBW equal to RBW is what you want.

I assume you are doing FCC 15.247 “The maximum permitted peak conducted output power is +30 dBm (1 W). However, the power spectral density conducted from the intentional radiator to the antenna shall not be greater than +8 dBm in any 3 kHz band during any time interval of continuous transmission. ”

To achieve this, I would use the following settings:
1) Spur reject off
2) Video detector set to min/max
3) 3 kHz CISPR / Gaussian RBW, 3 kHz VBW (in Spike, when VBW = RBW and min/max selected, there is no video filtering)
4) Trace set to max hold
After accumulating for several seconds, peak search. This should give you the correct reading. Let me know if I misunderstood the test you are running.

If you need triggered zero span (I/Q) acquisitions, I highly recommend the BB60C. Triggering on the SA44B is very limited and it is easy to lock up the device if you are not very careful.

We intentionally do not trigger sweeps, to avoid the situation where people try to sync a swept signal generator with our spectrum analyzer, because a stepped FFT-based spectrum analyzer, even perfectly synced, is only actively looking at the spectrum a fraction of the time.

The solution is to use our tracking generator, which has firmware to switch frequency at appropriate times for the architecture.

Bruce,
If you have not rebooted your computer since installing the driver, try that first. If you have, we can try the CDM uninstaller, to remove any history of the SA44B and get a fresh start.

http://www.ftdichip.com/Support/Utilities/CDMUninstaller_v1.4.zip

Unplug the SA44B, and then run the CDMUninstallerGUI
Use VID = 0403, PID = 6010, then click “Add” then “Remove Devices”
Plug in your SA44B and wait 3 minutes. Watch the LED. It should turn green once the driver finishes installing.
Let me know if this helps.

I don’t know if this will help, but making sure the driver is up to date may help. FTDI puts out a nice guide with some helpful troubleshooting tips: http://www.ftdichip.com/Support/Documents/InstallGuides/AN_396%20FTDI%20Drivers%20Installation%20Guide%20for%20Windows%2010.pdf

Raash,
Using just the open (or short) is suboptimal, and the directionality of your coupler limits the accuracy of your VSWR measurement. But it’s my understanding that correcting with open / short / load would require phase information, which we cannot acquire with a scalar system.

Raash,
For the Smith chart utility, the time bases must be locked, but the sync signal is not used. Only one BNC is required.
Connect the TG 10 MHz out to the SA external reference in, then enable external reference in the software. Note that on the SA series, with external reference enabled, do not remove the reference signal until after you close the software.

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