I have not seen this problem before, but your VSG should still be covered under warranty. Contact support@signalhound.com and we can set up an RMA for repair. I apologize for the inconvenience. If you bought it from a distributor, contact them for a repair or replacement unit.

Amy,

It is unusual to require more than 2 digits after the decimal for dBm readings, especially for small signals, where noise is going to dominate the reading. What type of analysis are you doing that requires that much precision? I would worry that our analyzers would drift more than this each reading.

This is definitely not normal. Is this the Spike application? Have you tried restarting it? If the problem persists, you may need an RMA for repair.

It looks like maybe the phase of your I/Q data doesn’t match up. Is this what you are seeing?

You should not expect the phase of two demodulated signals to line up. Even if the BB60s use the same external trigger and external time base, there is still a fractional-N PLL that can lock to several different phases each time you change the LO frequency.

Multi-channel phase coherent receivers exist, but they are generally more expensive.

If you need to make phase coherent measurements with two BB60Cs, generally you would:
1) Use a common external 10 MHz reference to align frequency
2) Use a common trigger to align time within 50 ns.
Now, all that is missing is phase alignment, and this is where it gets tricky.
3) Select your frequency on both devices, and begin streaming I/Q data. Do not change frequencies or interrupt the I/Q data stream for the next steps.
4) Send a known signal to both devices to calculate a phase offset (and possibly amplitude offset if needed) between devices
5) Connect your unknown signal. You can now measure relative phase between the two streaming devices, until you change frequency or the I/Q stream is interrupted.

Ramin,
At this point we do not have a software interface to automate Spike’s EVM measurements, but it is something we have talked about, and may eventually add.
Right now, you’d have to choose between reading the Spike software EVM manually, or using the API to capture I/Q data and something like Matlab or LabView (or other library) to compute EVM.

James,
If you rig it up such that the CPU fan blows across it, this may help keep it cool. It needs to dissipate about 6 watts, so if you insulate it too much the internal temperature will rise further. Some customers have mounted it to a metal plate, which can conduct heat away from the BB60C and provide more square inches for cooling…

If it were a TG124, one might further observe above 4 GHz, ‘M’, 0x02, 0xC0, and then dropping below 4 GHz, M, 0x01, 0xC0.

[Justin Crooks]

I don’t know how long it will take us to get to TG-linux compatibility, but if one were to snoop the USB bus, one would see setting internal reference out sends: ‘R’, 0x02, 0xC0. One might recognize 0xC0 as serial line internet protocol from way back.
Then one might set amplitude to maximum and observe ‘A’, 0x00, 0xC0.
One might finish by snooping to see that outputting 10 Hz sends ‘F’, 0x01, 0x00, 0x00, 0x00, 0xC0. One might then try 2560 Hz and see ‘F’, 0x00, 0x01, 0x00, 0x00, 0xC0.
One could then decide whether to wait for Signal Hound to implement Linux TG compatibility, or to forge on ahead.

• This reply was modified 9 years ago by Justin Crooks.

It sounds like the code for the TG is not working in Linux. I doubt the TG was tested in our Linux release, and there is probably some debugging that needs to be done. I will let the programmers know. The TG’s USB interface is FTDI 0403:6001.
Do you mostly need scalar sweeps, or CW signals, from the TG?

For a CW signal, image/spur reject ON should provide slightly better accuracy. The readings should definitely be within 1 dB of each other (e.g. image/spur reject off may be 0.4 dB high, on may be 0.2 dB low).

Your other settings are perfect for this measurement.

Ewald,
Unfortunately, there are some hardware limitations. The lowest clock to the I/Q DAC is 53.333 kHz, so for 1 kbps you could use 64 samples per symbol at 64 kHz. The down side of this is that with only 2048 samples, you could only have a pattern up to 32 symbols. The software we provide requires at least 127 symbols for a PN7 sequence, so we cut off at 4 kHz symbol rate. But using an arb file, you could generate a 1 kbps, up to 32 bit pattern sequence.

To do this, you would have to ensure a phase continuous waveform when it crosses back from sample 2047 to sample 0. This places some limitations on modulation index.

James,
We have certainly talked about this. Right now, it seems that USB-C is not very widespread yet, but as it becomes more popular there may be an off-the-shelf solution, or we may decide a custom adapter cable makes sense.

Sadak,
Yes, the resolution bandwidth, or RBW, is essentially the resolution of your frequency readout. For exact frequencies we have two tools: the frequency difference meter, and the modulation analyzer in zero span.

If you are looking for precise numeric calculations on an exact frequency, I would encourage you to use our API to acquire I/Q data, which can be processed to provide whatever measurements you desire.

For spans (not RBW) of 200 kHz or less, the LO frequencies are RF + 10.694 MHz and RF + 2.921 MHz. For spans greater than 200 kHz (up to several GHz), the LO frequencies are RF + 10.7 and RF – 10.7. In both cases the signal is sampled twice.

The 2.9 MHz IF is used when span is 200 kHz or less, to provide superior image rejection for narrow-band sweeps. It sweeps once with a 10.7 MHz IF, and once with a 2.9 MHz IF, and compares results to provide the cleanest spectrum possible.

Ivan,
That formula is quite accurate for flat top windows, but may be a fraction of a dB off for nutall and gaussian, due to the RBW shape.

Wizardek,
The IF frequency for the SA44B in fast sweep is 10.7 MHz. Image rejection works by injecting the LO low side (RF – 10.7 MHz), and then high side (RF + 10.7 MHz), and taking the lower reading for each bin.

Oh, sorry, I missed the bit about Windows XP. No, Spike (all versions) is only compatible with Windows 7 / 8 / 10. Our legacy software will work on XP.

Ramos,
Yes. Spike is compatible with all of our spectrum analyzer and tracking generator products. Some models may require a firmware upgrade, but this only affects a few percent of units.

JoeQSmith,
This is a very unusual problem. We will do what we can to help you via email. Trying a second computer is an excellent troubleshooting step. If the problem is limited to the Asus, we may be able to dig a little deeper. If not, we may just want to set up an RMA for warranty repair or replacement. Keep us posted.

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