After an open calibration, did you run a test with a 50 ohm load? Did you notice about a linearity on whole frequency range?
I did't but I checked it now
open first without calibration two -10db ( rx and tx) attenuators plus -16db of the coupled port -26db rx -10db tx total.
after calibration with two different 50ohms dummy load terminations, the yellow is the load from my calibration kit, the red one is from ebay, cheap both , both rated 6ghz
Yes, what you are doing is right.
This is open, for example:
73, Alberto
ok, after test as you advice in your picture, the problem is the same not consistent results at 5.8ghz , and do not look like the brands official antenna plots. I think could be the pluto sMA cable, it is rated 3ghz and if I pass the hand close this react quite energetic, is not possible my antennas do no get affected by it. Maybe could be bad satsagen settings by my part, just to be sure I tested my attenuators, directional coupler and all for me looks decent at 6ghz. Under 3ghz all looks good
thanks
Display MoreHi,
Thank you for your comment
We have added the -40 calibration feature to mitigate the imperfect region of -40dB due to the internal crosstalk of Pluto. The -40 calibration needs adding a good 40dB attenuator in the loopback after calibration of 0dB. SATSAGEN fire an error when read amplitude above the region of -40. Let aside for the moment the -40 calibration for your purpose of measuring return loss with coupler.
In my opinion, the problems you noticed should be due to the directional coupler. I suggest you find the best coupler for the characteristic of the DUT, in your case, the antenna. You should choose the coupler with the range frequency nearest your antenna, also this corresponds to the highest directivity value of the coupler.
If the directivity of the coupler is not sufficiently related to the typical return loss of the antenna, the results are errored.
The coupler directivity should be almost 10dB higher than the typical return loss of the antenna.
In my opinion, you should consider a directional coupler with about 23dB or higher of directivity.
In the picture of your post, the setup of Pluto and coupler is correct. With this setup (open), you can do a 0dB calibration, that it is sufficient to measure the return loss next.
The RX gain and TX power levels should be defined in the range where you use more of the dynamic of Pluto and less internal crosstalk.
I suggest you start with 30 of RX gain and -30 of TX pwr.
I suppose the antenna should be connected directly to the coupler because cables and connectors could affect the readings, but the antenna should be possibly free from interaction with other near objects. I know, it's not easy to do! Moreover, the Pluto without a metal case can be affected by antenna emissions!
In your picture, I see dipole antennas. The impedance matching of these antennas is it well done? If we ever manage to implement the VNA on SATSAGEN maybe we will measure this too!
73, Alberto
Thanks you so much by your answer, made me clear many things.
I took wrong the -40db calibration I thought it was the load calibration of a vna. ¿where you document this features? yeah would be cool can check the impedance I guess no idea how much important is that, I guess I will discover it soon XD..
When you say short or open, do you mean done with the calibration kit SMA dummies in the direc.coupler output and its coupled port always with the cable connected to RX (is what I'm doing)? or instead you mean close a loopback (short?) and after leave it open (open avg) with the SMA cable disconnected? if this last is the right way, the backloop is done from the coupled port I guess and if so should I put a short or load SMA dummy in the output (where I will connect the antennas)while the calibration is performed?
My couplers are OK, they are Narda or MAG with <1.5db insert loss and 25db of directivity. I have covered from 10Mhz to 8.6Ghz, I have cheap but good attenuators up to 6Ghz.
Thanks to your comment I think I found the nature of the weird readings, I was close to the antennas and the antennas and Pluto were over an aluminium table and close to a LCD TV. It just happened at 5.8ghz ISM, at 900mhz a was fine.
I made a provisional stand to test antennas, I will share how it works compared with the SWR antenna brand's charts.
What is sure I will learn a lot faster having your software an this awesome device.
Really I got crazy looking info to don't need ask by help but I could not get it. I'm sorry make all this questions with my poor english.
Infinite thanks.
Hi all,
some of the undesired components and images are derived from combined of nearby local oscillators RX and TX; unfortunately, this is a lack of the transceiver of Pluto as confirmed by ADI. These undesired components are not present at some span settings because the LO RX turns in sweep tuned mode, and they are out of scope of the chunks. Keep in mind that this behavior is mainly due to using RX and TX in loopback configuration with nearby LO.
73 Alberto
HI, thanks by your amazing software and dedication, could be this error I'm getting related with hardware limitations you said here? it gives error while -40db calibration, it did work in 1ghz speeds but not in the image test up 2-6ghz. Maybe it is a just a bad setting but I don't understand what mean the settings, and probably for what it is this calibration.My dummy termination loads are rated 6ghz and are two different models, maybe they are too cheap. Thanks again, always wanted learn to use lab tools, and know I can, really thanks
If I don't get it wrong then yes;After connecting the bridge, perform 1: short circuit 2: open circuit calibration at the reflection port.Then I was asked to measure the same 915MHz antenna for comparison.The results are as follows:
I'm trying to follow your instructions as I cannot find any others anywhere. but as I'm beginner I'm far from understand your instructions and apart now Satsagen has more calibration options. I have no basic knowledge so for me is even difficult understand the terms. I have a calibration kit and several good Narda HP dico.
1 Do I need put the coupler reversed? output is input? do I need connect the coupled port to the RX? is it "short circuit" done with the short from SOL kit?, where , in output or coupled port?
2 "open circuit calibration at the reflection port" : Do I need remove the cable from coupled to rx and put the OPEN dumy from SOL kit, or instead the Open dummy is fitted on output port?
3 What the AVG and -40db calibration enter in all this,
4 How affect gain and TXpow settings and why you have different settings in your pictures
Please could someone help me to understand how test antennas SWR on Satsagen? is it right how I have it connected? the tX is connected to out and I was connecting antennas and short,open from SOL kit in the INPUT port , the one is empty in the picture
