VSWR Station Usage Guide

Background

SWR (Standing Wave Ratio) is the ratio of the amplitude of a partial standing wave at an antinode (maximum) to the amplitude at an adjacent node (minimum). SWR is usually defined as a voltage ratio called the VSWR, but it is also possible to define the SWR in terms of current, resulting in the ISWR, which has the same numerical value. The power standing wave ratio (PSWR) is defined as the square of the VSWR.

Why do we need VSWR?

A problem with transmission lines is that impedance mismatches in the cable tend to reflect the radio waves back to the source, preventing the power from reaching the destination. SWR measures the relative size of these reflections. An ideal transmission line would have an SWR of 1:1, with all the power reaching the destination and none of the power reflected back. An infinite SWR represents complete reflection, with all the power reflected back down the cable.

This test measures VSWR value using an Agilent E5071C Network Analyzer (ENA).

Station Setup Guide

Set Up the VSWR ENA

1. Set the ENA's IP
   • Under Windows XP, Control Panel > Network Connection
   • Set it to 192.168.1.55/255.255.255.0
2. Enable the Telnet server on the ENA
   • System > Misc Setup > Network Setup > Telnet Server = ON

Set Up the Chrome Host

1. Install the Chrome OS test image into the host machine. If unclear on how to do this, refer to How to reimage the host? below.
2. Switch to VT2 by pressing Ctrl+Alt+F2. Log in to the Chrome OS with root / test0000.
3. Download factory toolkit, copy it to the host, and install. Example commands:

   # on your computer, using scp to transfer the file
   # (you can also use a USB stick to transfer the file)
   scp install_factory_toolkit.run root@${TESTING_HOST_IP}:/tmp
   
   # on the testing host VT2
   cd /tmp && ./install_factory_toolkit.run
   

4. Reboot the host, and select VSWR test list.

How to Reimage the Host?

1. Download the compressed test image file from CPFE
2. Decompress the file. Suppose you're working on a board named foo, and you were using version RXX-xyzw.p.q.

   tar xJvf ChromeOS-test-RXX-xyzw.p.q-foo.tar.xz
   

3. Write the image file into a USB stick by the following command:

   dd if=ChromeOS-test-RXX-xyzw.p.q-foo.bin of=/dev/sdx bs=16M
   

   Change /dev/sdx to your USB stick path.
4. Plug the USB stick into the testing host.
5. On the host, make sure it's in developer mode, and press Ctrl+u at the boot screen
6. Wait for it to boot, when finished, press Ctrl+Alt+F2 to enter VT2. Type:

   chromeos-install --yes && sync && reboot