STEP1: Rearrange data. Antenna measurements Nordic VHF Meeting, Íland 970606

(Feb 16 1998)

Why all these details ??

Since the method of measuring antenna performance by comparision of far field amplitudes and phases is not commonly used and since it leads to a considerable amount of data processing it is described in great detail here.

All data and software needed is presented in full detail in such a way that the evaluation process can be repeated by anyone interested. It is possible to investigate how sensitive different parameters in the computer model are to changes. For example it is possible to move the center of rotation along the boom or perpendicular to see if the change that occurs can be compensated by changing other parameters.

This site serves as a back up for software and general information about this method for later use at better sites than the one used at the Nordic VHF Meeting on Íland 1997.

Detailed description for rearrangment of data

Start by creating a new directory, for example C:\ANT. Then create a subdirectory for each antenna and give these subdirectorys names that agree with the different antenna names. Then copy the compressed raw data files, one to each subdirectory.

K1FO.ZIP
VARG13.ZIP
BSZ26.ZIP
VARG9.ZIP
17M2.ZIP
BSZ9.ZIP

Unpack the .ZIP files in their respective subdirectories. Unpacking will give several plain text files. Do not worry about these files now, just unpack them.

Copy STEP1.ZIP the source code and .EXE file for STEP1 into the main directory and unpack.

If you do not already have DOS4GW in your path, get it from here: DOS4GW.ZIP It is needed to run the .EXE file.

If you have a FORTRAN compiler, you may recompile the source code that is supplied with the .EXE file.

Once you have STEP1.EXE in the main directory, start it by typing DOS4GW STEP1.

The program will ask for a directory name. Type the name of one of the subdirectories. A lot of numbers will be written to the screen. The last 51 lines of the output contain the phase in the forward direction as a function of frequency.

If the parameter PATHLEN in the ANTPAR.TXT file is changed, (see below) the phase angle will change, and in particular, the phase will change more or less rapidly with frequency. The output waits for you to press "enter" so you can see the 51 last lines.

Pathlen is the total distance travelled by the signal from the AUT assuming speed of light in vacuum, so it is really a time. Different cables were used for different antennas, and the exact value for this parameter is insignificant. Any value that makes the phase reasonably constant will do.

When STEP1.EXE is run, the file CMPLXAMP.TXT is produced in the corresponding subdirectory. These files contain the rearranged experimental data in a form suitable for comparision with the theoretical model.

Zipped files to unpack before running STEP1

1234.DAT Measured data, output from the network analyser.
Here is a few typical lines from one of those files:

138.000 000 -43.367 dB -47.045 deg
138.200 000 -43.183 dB -110.27 deg
138.400 000 -42.956 dB -173.9 deg
138.600 000 -42.773 dB 122.2 deg
138.800 000 -42.624 dB 58.468 deg
139.000 000 -42.462 dB -5.4533 deg

The first column is frequency, the second is signal level and the third column is the phase angle. The 1234.DAT file contains the data measured at an elevation angle of 123.4 degrees.

0000H050M Measured data. Same format as 1234.DAT, but the data is not from a fixed height. The first 4 digits is the elevation angle and the last 3 digits is the height above ground for the AUT.

README.TXT Comments written soon after the meeting. Contains mounting position if we remembered to take down notes.

ANTPAR.TXT Parameters that are specific for this particular antenna.
An ANTPAR file may look like this:

PATHLEN      0  250.
HEIGHT      10  10.
ELCORR       0 -5.0
RZNOM        0  200.
BOOMPOS      0  4.252603  0.00001
BOOMOFFSET   0 -0.130162  0.00001
FIXPHASE     1  0.202115  0.00001
PHSINCOS  1010  0.00001
ANGCORR      0  0.00001
END

pos. 1 to 11 is a keyword
pos. 12 to 15 is a control number (without decimal point).
pos. 16 to 25 is the value for the parameter (with decimal point).
pos. 26 to 35 is the step size (with decimal point). The step size is used in the optimization process when the computer tries to find a set of parameters that will improve the agreement between the model and the measured data.

In STEP1 only the PATHLEN parameter is used. The other parameters are used in STEP2 and STEP3 and will be described later.

INPUT.NEC Antenna geometry in NEC2 format.

PARNR.NEC Tells if original or modified NEC2 should be used. Look at OMNEC for further info.

Z_1.DAT Impedances measured directly with the network analuser (for BSZ26 only).

PHSINCOS.TXT This file contains the phase as a function of frequency as a fourier expansion. It is generated by the optimisation procedure and will be discussed later.

MTANGFIX.TXT This file contains corrections to the measured angles. It is generated by the optimisation procedure and will be discussed later.