Rohde & Schwarz FPC1500 (FPC-COM2 kit) or Siglent?

[tautech]

You are doing great RBBNVNL9, so good that you even got a thank you from a RS Product Management Engineer.

Now for those that don't have this equipment this is is what the "log mode" is like:





And this is what a real log in frequency mode means to me:





I have both a SVA1032x and a FPC1500, and the former is like 10x more capable.

FYI, go to the Display menu and change the default Inverse screenshot setting to Normal. 
Love my SVA1032X too despite having the substantially more expensive SNA5004A as well.

150mm WiFi antenna getting a 10001 point Mag Loss full 3.2 GHz frequency sweep and marker set to Continuous Valley. Display menu open FYI.
Log axis set for shits and giggles.

[PartialDischarge]

FYI, go to the Display menu and change the default Inverse screenshot setting to Normal. 
Love my SVA1032X too despite having the substantially more expensive SNA5004A as well.

Thanks but I have it on purpose since I sometimes print the responses in paper.

[nctnico]

Let me just add that I'm not interested in continuing this topic anymore. Log frequency sweeps have been available for more than 30 years in SAs and it is a feature

None of the Advantest spectrum analysers I have (owned) have log sweep, so the feature isn't as common as you might think.

Also look at the difference in RBW from the pictures you posted. The R&S is set to 200Hz while the Siglent is set to 300kHz.

[tautech]

The R&S is set to 200Hz while the Siglent is set to 300kHz.

That's only a User setting and here's another an order of magnitude better.

[nctnico]

@tautech: your RBW is still at 30kHz. Not 200 Hz. Also the start frequency is at 9kHz, not 100Hz. In the end the images PartialDischarge has posted are not comparable in any way. Also look at the sweep times; with comparable RBW the R&S method still is quick while the Siglent is taking ages. Likely the Siglent does a linear sweep and plots the data on a log scale.

It would be interesting to see a log sweep from the FPC1500 with a higher RBW setting.

[jmw]

I own a FPC-1500 and the lack of log-frequency scale is seriously frustrating for characterizing filters or using it as a VNA. I'm hoping I can write a script to pull the raw data and do my own plot on a log scale next time I have to. While we're ragging on this instrument,

1. I had to send mine back three times because it would whine about an IF stage overload in VNA mode, when everything was in its default settings and nothing was attached to the ports. On the third time, I guess they finally said eff it and sent me back a completely new unit.
2. 1 Hz RBW is horribly bugged - as in signals can vanish from the screen going from 3 Hz to 1 Hz. The solution from R&S was to downgrade the firmware, and a year after this was documented they have not posted an update.
3. The vertical scale adjustment is annoyingly limited. If I have an example -20 dB filter, I can't look at the narrow range of -20 dB to -30 dB using the full screen, unless I dial in 20 dB offset (which makes it appear like it is 0 dB filter, quite confusing for documenting work for later review).
4. Narrowing the frequency range blows away any S11 calibration or S21 normalization without warning. At least it could attempt to interpolate instead of making me disconnect all cables, bring out the O/S/L standards, and reconnect everything.

It's truly frustrating because this instrument is quite expensive in its class (just under $10k fully loaded sticker price - I got mine under a promo, but still a lot of cash) and is capable of excellent raw RF performance, but is hobbled by crappy firmware that as @PartialDischarge noted, they would be blasted for if this came a Chinese vendor.

[nctnico]

In the end the images PartialDischarge has posted are not comparable in any way.

Of course they are not comparable in any way because the FPC1500 does not have a continuous log frequency sweep and the TG does not operate in this weird discrete receiver log frequency mode, and there is no way to obtain even similar graphs. The image I posted is what is sold as "log frequency" in this FPC1500. I wish you could have the FPC to test it and you would understand.

And the RBW does not matter: what the FPC1500 is doing is drawing vertical bars (yes solid bars from bottom to top) for each frequency, the RBW only affects the measure at that point not at the sides, its always drawn as a vertical solid bar. And this is a VNA not just a SA: In SA mode there is no log-freq scale option, and in VNA mode there is no log-freq scale option.

The 'bar' chart is a bit weird indeed. I would not expect that either. Maybe the idea behind it is that is doesn't pretend to have information about what happens to the amplitude between the steps. This looks like it is a bit of an in-between product where it comes to network analysis.

I own a FPC-1500 and the lack of log-frequency scale is seriously frustrating for characterizing filters or using it as a VNA. I'm hoping I can write a script to pull the raw data and do my own plot on a log scale next time I have to. While we're ragging on this instrument,

That should be quite easy to do with a bit of Python scripting. Recently I bought a similar device from a different brand and that doesn't offer log scale in VNA mode as well.

4. Narrowing the frequency range blows away any S11 calibration or S21 normalization without warning. At least it could attempt to interpolate instead of making me disconnect all cables, bring out the O/S/L standards, and reconnect everything.

In my experience that behaviour is quite normal for a VNA. Change any setting and your 'calibration' (IMHO a better term would be reference measurement) information is voided.

It's truly frustrating because this instrument is quite expensive in its class (just under $10k fully loaded sticker price - I got mine under a promo, but still a lot of cash) and is capable of excellent raw RF performance, but is hobbled by crappy firmware that as @PartialDischarge noted, they would be blasted for if this came a Chinese vendor.

As usual: always make sure test equipment does what you need it to do before buying (either through testing a loan unit and / or through in-depth reviews that address your use cases). AFAIK the FPC1500 has been on the market for quite some time already so I can understand your dissapointment that they have not addressed the issues you listed yet.