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DDR,
We digitally tune, so the frequency resolution is limited to a double precision floating point number (sub-Hz resolution). If you are asking about the tuning of the LO itself, we tune in 125/16 MHz steps (7.8125 MHz), and digitally tune from there. September 1, 2020 at 9:35 am in reply to: Using 10 dB coupler for return loss measurement & 20 dB pad placement Yes, but the scalar system for return loss only has the dynamic range of your coupler’s directivity, which is less than 40 dB. So it is not recommended to “store 20 dB pad” for return loss, only insertion loss.
August 31, 2020 at 12:06 pm in reply to: Using 10 dB coupler for return loss measurement & 20 dB pad placement Jeremy,
Your coupler will work fine. For return loss measurements, there is no reason to “store 20 dB pad” because 50 dB of dynamic range is more than enough for a return loss measurement.
For return loss measurements, if you have 3-6 dB SMA attenuators around, putting one on the TG and one on the BB can improve SWR which will make the measurements more accurate.Michael, this looks like the 140 MHz SAW band pass filter in the BB60C. Most of the ripple should generally be removed in our corrections, but there can sometimes be a little residual ripple which is somewhat worse as the device is warming up. Once the BB60C is fully warmed up, this ripple may be smaller.
Hopefully this helps. If you are looking for amplitude deviations smaller than 0.5 dB, you may need to wait for the device to warm up for 30 minutes, and then use trace math or some other mechanism to subtract out this baseline trace.
For what it’s worth, you should not see this ripple in the SM200B/C. We do not use any SAW filters, so the IF is smooth.It’s a Cypress FX3 chip, CYUSB3014
Kaiser,
I see two possibilities here.
1) The sheer data rate of the SM200B is causing problems, or
2) When you installed the software, you also installed the FTDI driver for our SA44B, which is somehow incompatible with the VN-310.If you re-install the VN-310 driver does it help? If you use FTDI’s “CDM uninstaller” with the VID/PID of the VN-310, and then plug it in, does it help?
Matthew,
I have never seen that before, but if you can write a little code, parse the wav file, probably window the data, do an FFT, threshold detect (1 for above threshold, 0 for below threshold), invert the threshold array, inverse FFT, then scale. I am not aware of an application for this, but if you have one, something like this would be a good way forward.Geev,
The I/Q pattern memory is pretty short (2k samples), but yes, a short Gaussian waveform is possible. You can also look at 1001 tones with random phase relationship, which will have many of the same properties as bandwidth-limited Gaussian noise.For a better Gaussian white noise generator, consider the VSG60A.
Kefei,
There are a few ways to do this. You could record the sweeps in Spike (you may need an SM200 in real-time mode, span >160 MHz, for 1 ms sweeps).
For more control, you could simply record 1 second of I/Q and do your own windowed FFTs. With the SM200B, this would give you up to 2 seconds at 160 MHz span.
A third option is the waterfall spectrum plot in zero span mode. In this mode, the biggest limitation is probably the 1 second requirement. This would set a pretty low I/Q sample rate, since you are limited to a few million I/Q data points.Volker,
Yes, this is something we have discussed. It is not something we have scheduled at this point, but it is definitely something we hope to add in the future. It would probably not be one of our existing tracking generators, but something geared towards the frequency range and performance of the SM series.Gary,
There are a few things going on here. It sounds like you are aware there is no baseband reconstruction filter on the VSG25A. But we also apply an inverse sinc correction to the in-band data to flatten it.
PN9 is a PRBS9 sequence (linear feedback shift register) that basically repeats every 511 symbols. We upsample each symbol by a factor of 4 to produce 2044 I/Q samples, which get transmitted in a loop.
Even with no raised cosine filter, the upsample process will result in gaps in the sin(x)/x curve.
Hopefully this helps.If it helps there are schematics online. Typically a 1 Mohm input impedance to a non-inverting unity gain op amp, with a 50 ohm series resistor (or resistor to bring it to 50 ohms) on the output. You may want to add a ceramic [0.1 – 10] uF DC blocking cap, depending on your low frequency coverage needs.
We have a probe that works from about 100 kHz to 4 GHz, with about a 500 ohm AC load to your circuit (DC blocked). We are not set up for a FET probe, which would be what you would need for a high impedance load to your circuit but a 50 ohm output impedance. This is more of an oscilloscope function.
Kefei,
To convert I/Q data to spectrum, you will need to perform overlapping windowed FFTs. Typically what this looks like, if you are doing a 1024-point complex FFT, is every N samples (for your application this would be every 1 ms), you will take the last 1024 I/Q samples, window them (multiply by a window function, like a flat top or hamming window), and then FFT them to generate a spectrum.
We have not interfaced SDR sharp. One approach would be for your friend to develop a plugin, to connect the BB60C to SDR# directly. Another would be to use our API to save I/Q data as a WAV file and try to play that in SDR#.
Basically, queued fast sweeps just go. Unfortunately there is a little bit of uncertainty each time the LO changes. We check to see if it has settled, and add a few microseconds delay if it has not, so even if they started in sync it would not last.
We could add this to our list of feature requests. Most likely this would be a feature we would add to a future product (multi-channel receiver) due to the complexities of synchronizing two standalone devices.
If you could scan your spectrum more slowly, 40 MHz at a time, you could use I/Q streaming and a shared external trigger to get them sync’d within a handful of nanoseconds.
Keysight has a good IP3 guide: https://www.keysight.com/upload/cmc_upload/All/ENA_IMD_Measurement_Summary.pdf
That model should work just fine. A 10 MHz square wave will provide slightly better performance, but it looks like the output is +10 dBm or higher, which is good.
For what it’s worth, I get 375 ms on my PC for the same sweep. Unfortunately, sweep time, especially on narrow spans, is not deterministic. There are settings applied, and then acknowledged, several times per sweep. So the timing will vary based on your USB read/write latency, which can vary for a lot of reasons. Spans of several MHz will generally be more consistent since the sweep is controlled more in firmware than software.