Antenna Test Data 4 Bay

[gary350]

I used the field strength meter on my HDTV to get these readings. The frequency on the left are the 3 channels that I tested it shows a frequency range between 186 to 692 MHz. The antenna screen is 20" wide 36" tall. The elements are 5" from the screen and spaced 9.5" apart vertical and 1.5" apart horizonal. I am using a 300/75 ohm balun and 6 ft of 75 ohm coax to the converter box. The element length and space between the whisker tips were changed to find the maximum signal strength. This test was repeated 3 times. The signals became more stable in the evening after the sun went down. After the first test I saw a noticable pattern the best signal was from element lengths 9" long and 10" long. I also noticed the best signal was whisker spacing of 3" and 4" apart. This test took place upstairs in the house about 18 ft above the ground. The antenna was rotated to pick up maximum signal strength for each element length and each whisker spacing.

Elements length = 8"
Inches between whiskers........2".............3".............4".. ...........5"
692 MHz signal strength........37.............35............38... ..........36
482 MHz signal strength........63.............62............64... ..........65
186 MHz signal strength........42.............40............43... ..........41

Elements length = 9"
Inches between whiskers........2".............3".............4".. ...........5"
692 MHz signal strength........38.............38............43... ..........41
482 MHz signal strength........64.............65............67... ..........67
186 MHz signal strength........49.............51............52... ..........52

Elements length = 10"
Inches between whiskers........2".............3".............4".. ...........5"
692 MHz signal strength........34.............35............39... ..........38
482 MHz signal strength........67.............66............68... ..........65
186 MHz signal strength........56.............55............57... ..........57

Elements length = 11"
Inches between whiskers........2".............3".............4".. ...........5"
692 MHz signal strength........38.............36............36... ..........39
482 MHz signal strength........66.............68............69... ..........64
186 MHz signal strength........44.............53............53... ..........52

A final test was done using only elements 9" and 10" long spaced 3" and 4" apart.

Elements length = 9"
Inches between whiskers........3".............4"
692 MHz signal strength........35............34
482 MHz signal strength........62............61
186 MHz signal strength........51............50

Elements length = 10"
Inches between whiskers........3".............4"
692 MHz signal strength........34............34
482 MHz signal strength........68............64
186 MHz signal strength........49............50

Next I did one more test I made the screen larger from 20"x36" to 36"x36". The signal became much more stable. Fluxuation in signal changed for example, 67 to 69 are now holding steady at 71. There was almost no noticable increase in signal strength at 692 MHz.

Elements length = 9"
Inches between whiskers........3".............4"
692 MHz signal strength........32............33
482 MHz signal strength........65............66
186 MHz signal strength........69............69

Elements length = 10"
Inches between whiskers........3".............4"
692 MHz signal strength........39............34
482 MHz signal strength........69............69
186 MHz signal strength........71............72

Next I experemented with the element diameter #14 wire, #10 wire and #8 wire. No signal difference was noticed.

http://i43.photobucket.com/albums/e358/gary350/Ant-Test.jpg

 

[Don_M]

Nice-looking build quality there! :thumb:

It's not surprising that the wider screen aided signal stability. Your tests demonstrate that a 20-inch screen behind 10-inch whiskers (or longer) isn't really wide enough to act as a proper reflector for the active elements, particularly on lower frequencies. The wider screen sure gave a nice bump to channel 9, didn't it?

Thanks for sharing that. You put in a lot of work on this project, and it shows. :first:

 

[M4ny]

Nice job on the testing it really falls in line with a lot of the stuff I've discovered through computer modeling and testing that style antenna as well.
Changing the whisker opening is somewhat like changing the effective length of the whisker. The effective length is pretty much measured from the center line of the antenna to vertical line drawn between the tips of the whiskers. There is also a bit of a change in element (whisker) impedance as well especially in very wide 5"+ or narrow spacings 2" or less for that size whisker.
Changing the wire size as you saw doesn't do much of anything within that range, the V shaped whisker is more of a factor in bandwidth than wire size and the currents and voltages riding on the elements are so small about any size wire could handle it.