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Timed plots


Make sure that the 'Triggered' checkbox is not selected.  When Triggered is selected PolarPlot will only take readings when a trigger pulse is received or the Manual Trigger button is clicked - not what you want for timed plots.  Triggered mode is not the same as Auto Start or Auto Stop.

The program has an optional automatic feature that can sense the start and end of a plot according to presence or absence of a received signal.  Refer to Automatic start/stop for a description of how this operates and how to customise the triggering characteristics.

a) Enable or disable auto start and auto stop by clicking in the appropriate checkboxes.  If you are measuring a remote antenna it is convenient to use the automatic start/stop facility because the remote operator knows when he is starting and stopping his rotator, and he can co-ordinate the rotation with the timing of his transmission.  If you are measuring your own antenna then the choice is yours - manual or automatic.

b) Without altering any of the gain settings, the beam to be measured should then be turned to one end of the rotator travel.
 
You will get a better indication of beamwidth if the main lobe of the antenna being measured is not initially pointing towards the signal source, but is oriented with the side or back of the beam facing the transmitter.  The reason is that most rotators actually swing more than 360 degrees, and it is easier to see how many readings to trim when the signal level is changing level.

Also, if you trim readings from the main lobe within the 0 to -3dB points you will be affecting the observed beamwidth and hence affect the calculation for estimated gain.

C1) Manual Control

If not already transmitting, start transmission.

Start antenna rotation and at the same time clicking on 'Collect data' to start the program collecting readings. 

At the end of the antenna's rotation, click on the 'Halt collection' button. Collection will automatically cease after 360 readings, so if you have got the antenna rotation time the same as the program collection time then collection stops at the correct moment automatically.

Stop transmission.

C2) Automatic Control

Stop transmission

Click on 'Collect data'

Start transmission at the same time as commencing antenna rotation.

At the end of the antenna's rotation stop transmission.

At the conclusion of the plotting run the readings taken will be shown as a series of dots on the plot. At this stage it may not look much like a polar diagram - that appears when you perform a 'Rescale' operation.

If you have used automatic start/stop there is likely to be a blank area at the end of the plot where the computer has ceased to take measurements after the rotator has reached the end of its travel and transmission has ceased.

If you have used manual start stop you may have a series of readings at the start and end of the plot when the rotator was not moving.