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For latest information
on Australian Beacons visit www.vklogger.com
BUILDING ANTENNA'S? Download VK5DJ's YAGI
CALCULATOR
Many successful antennas have been built using this beaut little program
designed by John VK5DJ. You can download the program here - Yagi
Calculator
John comments, "With a move away from DOS to the Windows environment it
became clear it needed an update. I also took the opportunity to update a couple
of the algorithms".
The new version is again based on the work of DL6WU. It is meant to calculate
the dimensions of long yagi antennas (2 or more wavelengths) for VHF and UHF.
Dimensions, Gain, Stacking Distance, and Matching are covered. A simple SWR
calculator is included. The help file covers some of the issues involved in yagi
construction. The program works in all screen definitions
but is best at 1024*768.
Measuring the Vertical Pattern of an Antenna by
David Smith
I'm taking advantage of the noisy Sun to measure my antenna pattern (well, I
can't hear anyone up north in the morning, so something to keep me amused). This
is of interest to me because I have a go at JT65 EME contacts from time to time,
and it's nice to know what the antenna is doing as the moon goes down (or comes
up) - I don't have the luxury of elevation control (yet).
For those who might be interested in how their antenna performs, this is what I
did:
- You'll need a recent version of WSJT (why not the latest - 4.7.0)
- Select EME Echo mode and click on the Measure button. The program will
now show the received noise level at 2 second intervals.
- Turn your antenna to a quiet part of the sky and adjust the Rx Level to give a
reading around 0dB (not critical, but that can be the reference background noise
level).
- Now turn the antenna towards the Sun. WSJT will tell you what Az that
should be, and it's a good opportunity to check the accuracy of your beam
heading indicator
- The best time to start measuring is either 10 mins before sunrise, or a bit
over one hour before sunset. That way, you'll get from about 10 degrees
elevation down to below the horizon.
- Click on Erase to clear everything out, then click on Measure to start reading
the noise level. Note down the time and Sun elevation at the start.
- You might need to tweak your beam a couple of times during the next hour or
so, to keep it pointed directly at the Sun. Depends on how sharp your beam
is.
- When the Sun has set, or got up above 10 degrees (or you're sick of it), it's
about time to stop. Note the Time and Sun elevation again.
- Now Copy the results from WSJT. Click to the right at the very end of
the list. Then scroll back to the top and Click at the very start while
holding down the Shift key. This'll highlight all the results. Press
Control C to copy into the clipboard.
- Now to get them into Excel. I find it easier to go via Word. Paste
the clipboard into a blank Word doc. Then remove spaces by Replacing
double space with space until no more replacements happen. Then convert
Text to Table using space as the delimiter. Finally, copy the table and
paste it into a blank Excel spreadsheet (Phew!)
- Insert a column to the left of the noise level results, ready for the
elevation data. I used the assumption (which is pretty close) that the
elevation changes at a constant rate. So, work out the rate of change of
elevation (degrees per second) using the start and end elevations and times.
Enter the start elevation at the top of the elevation column. Then in the
next box down, enter a formula = elevation from box above +/- rate of change
(depending on whether sun was rising or setting). Don't forget to multiply
rate of change by 2 because measurements are at 2 second intervals. Then
highlight from the formula down to the bottom of the column and use Control-D to
fill the column with that formula. It should now show elevations that make
sense.
- You can now graph the results by highlighting the two columns (elevation and
noise level) and using the Insert -> Chart -> XY Scatter. Voila, the
vertical pattern of your antenna! (hopefully)
My results show a nice set of peaks and troughs for the first few degrees.
So, now I know roughly when I'll get the best signal from the moon.
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