10
If you do not know the VF of the coax you are using, you must directly measure the electrical
length of the coax you have or obtain cable with a known VF. The DX Engineering
DXE-F6-1000
75 Ω coax has a nominal VF of 0.85. For best performance, the coax for the delay
lines should be from the same batch or spool.
The first step is to determine the required
electrical
length of DLY3. This is based on the corner-to-
corner or diagonal distance between two diagonal corner elements of the square forming the array.
You can directly measure this distance, or it can be calculated by multiplying the side length of the
array by 1.4142. The
electrical
length of delay line DLY3 should be slightly shorter than the actual
physical distance between the two diagonal corners of the array. An electrical length 95% of the
physical distance works well (diagonal distance times 0.95).
Table 2
shows these calculations for
three common side lengths.
Side Length in Feet
Diagonal
Physical Length
in Feet
Factored 0.95
Electrical Length
in Feet
DLY3 Physical Length
in Feet (0.85 VF)
270 (900 kHz)
382
363
308.4
135 (160m -1.8 MHz)
190.9
181.4
154.2
98 (160m & 80m)
138.6
131.7
111.9
70 (80m - 3.6 MHz)
99.0
94.0
79.9
35 (40m - 7.2 MHz)
49.5
47
40
Table 2 - Examples of DLY3 Required Length
After calculating the required electrical length, you must include the VF of the coax being used
when determining the correct physical length of DLY3. Multiply the factored electrical length by
the VF. The result is the correct physical length for DLY3. See
Figure 4
and the sidebar for an
example.
Note:
These calculations are in feet, not feet and inches.
To find the physical length of DLY3, calculate the diagonal
length of the array by either directly measuring the
diagonal or by multiplying the array side length by 1.4142.
DLY3 will be significantly shorter than the actual physical
length. The diagonal length is first multiplied by 0.95.
This gives the factored electrical length for DLY3. Next,
multiply the DLY3 electrical length by the VF of the delay
line coax. The result is the correct physical length for
DLY3.
Figure 4 - Diagonal Dimension
For Example
: An array with 90 foot side spacing, the diagonal length is 127.3 feet. The 0.95
factored physical length for DLY3 electrical length is 120.9 ft. Multiply 120.9 ft.
by 0.85 (the VF of DX Engineering 75 Ω coax).
The correct physical length for DLY3 is 102.77 feet, or 102 feet 9 inches.
