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Re: Antenna analyser

Posted: Tue May 31, 2016 9:11 pm
by Drachenfrucht
By the way: How do I load/open/view a saved .s1p that I saved before with "Vector Network Analyzer" program?

Re: Antenna analyser

Posted: Tue May 31, 2016 9:25 pm
by pavel
Drachenfrucht wrote:By the way: How do I load/open/view a saved .s1p that I saved before with "Vector Network Analyzer" program?
The .s1p files can be read and analyzed with programs like HamVNA, PyTwoPort, scikit-rf, ADS, etc.

Re: Antenna analyser

Posted: Tue May 31, 2016 9:48 pm
by Drachenfrucht
Ok works. Thank you. Pavel, do you think that you will make your program work with HamVNA in future, again? Or definitely not? HamVNA is really cool and I also like the RLC fit. Just a question :p

Re: Antenna analyser

Posted: Tue May 31, 2016 11:02 pm
by pavel
Drachenfrucht wrote:Pavel, do you think that you will make your program work with HamVNA in future, again? Or definitely not? HamVNA is really cool and I also like the RLC fit. Just a question :p
It depends on what program you're talking about.

If it's the SDR transceiver, then it's most probably not. Unless somebody explains me what is missing and how to implement it.

If it's the new VNA application, then it's not impossible to modify HamVNA and to make it to communicate with this new VNA application. The main problem is the price of the Delphi compiler required to recompile HamVNA. It's 392 euros for the starter edition. I've tried to recompile HamVNA using Lazarus/FPC but without much success.

Re: Antenna analyser

Posted: Wed Jun 01, 2016 1:07 pm
by greggdaug
A balun's loss can be approximated using a reflection measurement:
balun_sim1.png
balun_sim2.png
Note that the balanced side is terminated with 50 * T^2 ohms.

The most accurate way is to use the back to back technique with a transmission measurement.

Using Pavel's program, one would have to save an s1p file and then extract rho (S11) into an exel file to perform the gain calculation.

Re: Antenna analyser

Posted: Thu Jun 02, 2016 9:55 am
by greggdaug
Forgot to mention that Qucs is a very nice free circuit simulator.

http://qucs.sourceforge.net/

Re: Antenna analyser

Posted: Sat Jun 11, 2016 10:09 am
by fisafisa
Hi
Just an idea, probably silly.

Instead of using a bridge with a transformer/common mode rejection circuit,
why not simply acquire both branches of the bridge using the 2 RPI inputs?
One will simply be 0.5 Vin
The other will be Vin /(50 + Z) * Z.
By looking at the phase and amplitude one can measure Z.
In fact, if one could rely on the Zout of RPI, one would not need to measure Vin...
In that case one could duplicate the circuit and make a 2 port measurement.

Just a silly idea, but I cannot be convinced we need a complicated bridge since we have 2 ports?

Regards

Re: Antenna analyser

Posted: Sun Jun 12, 2016 12:16 pm
by greggdaug
A simple divider will work with both Vin and Vdiv measured. This type of fixture suffers from measurement errors similar to the bridge or series fixtures. The fringing capacitance associated with the open standard and the ADC input capacitance contribute to this error. Below is a simulation showing the percentage measurement error (at 60 MHz) for three DUTs. Rdut = 1 - 2000 ohms, Cdut = 1 - 2000 pF and Ldut = 1 - 2000 nH.

Sim schematic
div_sim1.png
Sim results
div_sim2.png

Re: Antenna analyser

Posted: Sun Jun 12, 2016 3:52 pm
by fisafisa
....what about introducing a RC parallel network to create a 1:10 attenuator (like in a probe)?.

If I understand your message, it is better to have the two branches of the bridge as the effect of the measurement system is the same for both?
So we could use the two inputs of the RP instead of the common mode filter?

Re: Antenna analyser

Posted: Tue Jun 14, 2016 8:35 am
by greggdaug
Yes, it is possible to utilize the two RP inputs and eliminate the common mode choke.

A 10:1 probe will incur a 20dB loss, but could be used to reduce the input capacitance of the ADC inputs. To maintain sufficient bandwidth, the ADC inputs would have to be terminated in 50 ohms.
probe_10to1.png