15
directly measure the electrical length of the coaxial cable you have or obtain cable with a known
VF. The included DX Engineering
DXE-F6-1000
75 Ω coaxial cable has a nominal VF of 0.85. For
best performance, the coaxial cable 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 3
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)
135 (160m)
190.9
181.4
154.2
98 (160m & 80m)
138.6
131.7
111.9
70 (80m)
99.0
94.0
79.9
Table 3 - Examples of DLY3 Required Length
After calculating the required electrical length, you must include the VF of the coaxial cable 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 coaxial
cable. The result is the correct physical length for
DLY3.
Figure 4 - Array Diagonal Dimension
