Antenna analyser

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greggdaug
Posts: 26
Joined: Wed Jun 10, 2015 1:40 pm
Location: United States

Re: Antenna analyser

Post by greggdaug » Fri Apr 01, 2016 9:53 am

Here is an idea for a 2-port VNA. I have this mostly working using Scilab / NFS.

I have used this as a 1-port for making antenna impedance measurements.

I will post some results and scilab scripts when I have time to clean up the code.

-Gregg - WB6YAZ
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Drachenfrucht
Posts: 34
Joined: Fri Mar 18, 2016 12:18 am

Re: Antenna analyser

Post by Drachenfrucht » Sat Apr 02, 2016 8:19 am

Hi Pavel and thanks for your feedback and thanks for your effort and the the great software you develop ;)
Thanks also to Gregg for the attached PDF.

Gregg, can you post some more information, please? Unfortunately I am not so experienced as you. If I understood correctlyIs I should need a "reflexion bridge" like shown on the HamVNA webpage, right? Can I purchase such a "reflexion bridge" somewhere? I have no skills to build one on my own :(

My goals with the RP are:

(1.) I want to connect an antenna to the IN port and show on which frequencies the antenna is resonant.

(2.) I want to use the LCR meter and measure the impedance across a frequency range. The VSWR is also interesting for me. So do I need LCR meter from RedPitaya or do I need HamVNA or both? :)

I want to add that I installed HamVNA and successfully connected to Pavels' HPSDRtransceiver application. But I think I need (1) a reflexion bridge and (2) a shunt resistor. Where can I purchase these parts needed to achieve the goals?

Thank you so much in advance. Wish you a nice weekend.

pavel
Posts: 542
Joined: Sat May 23, 2015 5:22 pm

Re: Antenna analyser

Post by pavel » Sat Apr 02, 2016 10:49 am

I don't have much experience with VNA, but I have a couple of ideas :D

A series fixture could be made of two scope probes, two T-connectors and two 50 Ohm terminators. Something like on the following image:
series_1.png
A simple bridge could be made of three 50 Ohm resistors and one common mode choke:
bridge_1.png
The common mode choke could be just 5-10 turns of bi-wire or coaxial cable wound on some plastic cylinder (5-10 cm diameter). A plastic bottle or a plastic pipe.
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pavel
Posts: 542
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Re: Antenna analyser

Post by pavel » Sat Apr 02, 2016 3:38 pm

pavel wrote:The common mode choke could be just 5-10 turns of bi-wire or coaxial cable wound on some plastic cylinder (5-10 cm diameter). A plastic bottle or a plastic pipe.
Just found a web page with many pictures of air core chokes:
http://www.hamuniverse.com/balun.html

Hopefully, they'll help to build a simple bridge.

Drachenfrucht
Posts: 34
Joined: Fri Mar 18, 2016 12:18 am

Re: Antenna analyzer

Post by Drachenfrucht » Sat Apr 02, 2016 10:23 pm

Hi Pavel,

thanks a lot for your effort and the detailled description. I also did research on Google and I did find this reflection bridge for 36 EUR. A german documentation is available as PDF.

Could I use the mentioned reflexion bridge for my goal?

Thanks a lot and a nice weekend
Saki

pavel
Posts: 542
Joined: Sat May 23, 2015 5:22 pm

Re: Antenna analyzer

Post by pavel » Sat Apr 02, 2016 10:56 pm

Drachenfrucht wrote: A german documentation is available as PDF.
Could I use the mentioned reflexion bridge for my goal?
I could not find any schematics of the bridge in the PDF document. So, I don't know how to compare it with the bridge suggested by the author of the HamVNA program.

Is there any particular reason that you need the reflection bridge?

The series fixture is easier to build (just a few resistors) and even the author of the HamVNA program writes that he uses the series fixture more often because it works both in the transmission and reflection modes.

I've just tried two scope probes as a series fixture. Using my RX antenna as a DUT I could see some resonances. Unfortunately, I don't have any reference antenna analyzer or VNA to compare with.

greggdaug
Posts: 26
Joined: Wed Jun 10, 2015 1:40 pm
Location: United States

Re: Antenna analyser

Post by greggdaug » Sun Apr 03, 2016 5:31 pm

Here is some info on the dual directional coupler method. Binocular cores can be obained from Fair-Rite or Amadon. These are fairly easy to construct and work well below 200 MHz or so.
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greggdaug
Posts: 26
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Location: United States

Re: Antenna analyser

Post by greggdaug » Tue Apr 05, 2016 1:00 pm

Pavel,

Have you been able to use the HamVNA software to connect to your RP/HPSDR implementation? I get a 'no response from VNA' error when attempting to connect.

The powerSDR mRX PS program works fine.

Thanks,

-Gregg

pavel
Posts: 542
Joined: Sat May 23, 2015 5:22 pm

Re: Antenna analyser

Post by pavel » Tue Apr 05, 2016 1:46 pm

greggdaug wrote:Have you been able to use the HamVNA software to connect to your RP/HPSDR implementation? I get a 'no response from VNA' error when attempting to connect.
Most of the time HamVNA finds my Red Pitaya board without any problem. I can even make some plots as, for example, shown at the following link:
https://github.com/pavel-demin/red-pita ... -174176177

Rarely, when I have some connection problems with the HPSDR programs, they are solved by restarting the SDR application running on the Red pitaya board.

My network configuration is very simple: laptop and computer are both connected via wired Ethernet to a small router. I'm running HamVNA under Windows 7 without any virtual machines.

greggdaug
Posts: 26
Joined: Wed Jun 10, 2015 1:40 pm
Location: United States

Re: Antenna analyser

Post by greggdaug » Wed Apr 06, 2016 1:09 pm

The problem appears to be associated with Windows 10. I tried a Win7 machine and this works fine.

Also, there appears to be some confusion as to how HamVNA can be used with the RedPitaya. The HERMES hardware appears to have an internal coupler which is used as a reference. It is not clear to me how the reference is created using the RP. I looked at your plots and they do not make sense in relation to the loads you present. Enclosed is an s-parameter sim for the three cases.
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