Very nice, really helpful to see them side by side like that. Did you do a sneaky mirror on the images to make them match?
[...]yet highly surprisingly it's not located directly at the port but behind a switch and an impedance matching network / attenuator. I wonder how good the isolation/directivity characteristics of the circuitry are. If you look at the efforts the "big brands" in their boat anchors took some 25+ years ago to achieve really good directivity (see attached photo of an opened-up coupler of a HP 85046B test set, belonging to a 8753C VNA), it's hard to believe that despite all the advances in microcircuitry, manufacturers were able to shrink an assembly that much without sacrificing some quality/performance... I may be wrong, though .
What's also quite peculiar is that apparently Siglent got away with a single receiver channel. In order to get a proper phase relation between the measured signal from the DUT and the output signal provided by the VNA, the VNA would have to make a correlation of a portion of the generator signal to the measurement signal. For that purpose, "classic" VNAs have at least two input channels, one of them labeled "R" for "Reference". Since the SVA1015X clearly has only a single channel (with some switching circuitry albeit), it must manage the comparison between reference and measurement signal via that single channel in a multiplexed manner, making sure that the generator's phase is stable enough while "looking" at the measurement signal that no siginificant phase error is introduced during that time
Does the VNA option include the calibration KIT?
In Dave's video at 19:02, there's a close-up of the Port1 interface shown. Since I didn't quite believe that Siglent got along without a directional coupler for their VNA functionality, I dared to have a closer look, see the attached screenshot. There is a tiny multilayer coupler installed (similar to this one https://www.mouser.de/datasheet/2/400/tdk_02022018_HHM22152A2_ver4_1(Oct.2017)-1284660.pdf
Doesn’t require a full second receiver, all you need is to compare the phase out of the tracking generator to the phase at the input port.
Dave, thanks for the teardown, that was quite interesting.
In Dave's video at 19:02, there's a close-up of the Port1 interface shown. Since I didn't quite believe that Siglent got along without a directional coupler for their VNA functionality, I dared to have a closer look, see the attached screenshot. There is a tiny multilayer coupler installed (similar to this one https://www.mouser.de/datasheet/2/400/tdk_02022018_HHM22152A2_ver4_1(Oct.2017)-1284660.pdf), yet highly surprisingly it's not located directly at the port but behind a switch and an impedance matching network / attenuator. I wonder how good the isolation/directivity characteristics of the circuitry are. If you look at the efforts the "big brands" in their boat anchors took some 25+ years ago to achieve really good directivity (see attached photo of an opened-up coupler of a HP 85046B test set, belonging to a 8753C VNA), it's hard to believe that despite all the advances in microcircuitry, manufacturers were able to shrink an assembly that much without sacrificing some quality/performance... I may be wrong, though .
In contrary to the high bandwidth SSA3000 series, Siglent doesn't use the special Rogers (or equivalent) high frequency PCB material but rather some impedance-controlled FR4.
Yes, in principle you are right. But how does one (the instrument) "know" the phase at the tracking generator output?. After all the mixers, gain blocks and filters, even though in theory it may be possible to calculate it, you can not be sure to even getting close to the accuracy required for a VNA to provide reasonable results. You've just got to take a part of the output signal and analyze it to get the required phase information.
[...]
As to phase stability, Siglent does not specify it but you can probably measure it yourself and see how much/minute it drifts after a calibration.
It has to be said that the quality of your measurements depends on the quality of your cal kit. You can't measure a return loss of 50dB if your load has a return loss of 40dB! If you do measure 50dB after calibrating with a 40dB load, all you can say is the return loss is 40dB or better, subject to the VNA's measurement uncertainties.
It has to be said that the quality of your measurements depends on the quality of your cal kit. You can't measure a return loss of 50dB if your load has a return loss of 40dB! If you do measure 50dB after calibrating with a 40dB load, all you can say is the return loss is 40dB or better, subject to the VNA's measurement uncertainties.
Actually I think that the "quality of your measurements depends on the quality of the characterisation of your cal kit ".
As long as you have good data for your kit, then theoretically the actual standards themselves don't matter much.
Particularly true now that full S param files can be used on a computer, instead of the C0,C1 etc in approximate curve fitting in the VNA.
You can literally use anything as long as you have an S param file for it.
I'd start with a wider span next time so you can actually see the true resonant frequency. It's always nice to see that "dip" on the screen.
No, the monopole on the hockey stick.
No, the monopole on the hockey stick.
So this one?
Do you have a better picture of the actual antenna or is it just a piece of metal sticking upright? Where is the coax shield connected?
You can easily convert it to a groundplane antenna by using 3 or 4 equal length wires connected to the coax shield and pointing down like this:
I still think your SWR sucks…