Topographical Considerations - DX Engineering DXE-RCA8C-4S-INS Manual

To determine the Delay line length for an array which will be used over more than two bands, use
the highest frequency to be covered by the array in this calculation:
(983.6 / Frequency in MHz) x (.375) = Eight Circle Array Radius in Feet.
Then, Eight Circle Array Radius in Feet x (sin 22.5 degrees) x 2 = Adjacent Element
(Endfire Cell) Physical Spacing in feet.
The delay line physical length is then calculated as, Adjacent Element Physical Spacing in
feet x VF of the coaxial cable. The result is the correct physical length for the Delay Line to
be used on a three-band array, as shown in the example for a three-band Eight Circle Array
in Table 4.
Band Coverage
Desired
160, 80 and 40 meters
[ 983.6 / 7.3 x 0.375 = 50.53
Table 4 – Example delay line length calculation results for a 3:1 or greater frequency coverage
The DX Engineering DXE-RCA8C-1 uses a time delay system, not a traditional phasing system.
The delay line length is dictated by array dimensions rather than operating frequency, which allows
for the use of a single delay line for optimum directivity over a very wide frequency range. This
results in phase being correct for a rearward null at any frequency.
The delay line cable can be neatly coiled in a 1-1/2 ft diameter coil. Support the weight of the coiled
cable by taping or securing it to the support pole or mast rather than allowing it to hang from the
connectors.

Topographical Considerations

Flat land is best. Erecting the receiving array on sloped land or steep hills may degrade
performance. To avoid pattern degradation, antenna elements must have reasonably similar
elevations. It's recommended the ground height difference between any element in the array be less
than 10% of the array diameter. For example, a 100 foot diameter array should be within ten feet of
level. Every effort should be taken to make the elements symmetrical. Elements should all be
identical in construction and grounding, and should be mounted above any potential standing water
line but as close to the ground as possible. In general, the system will not be affected by trees or
foliage as long as the foliage does not contact the element. Ideally, in important receiving
directions, there should be a clear electrical path for at least 1-wavelength. The site should allow a
ground system to be evenly distributed around each antenna, if one is required, as for passive
elements.
Eight Circle Array
Radius in Feet
(.375-wavelength for
7.300 MHz)
50.53
50.3 x 0.383 x 2 = 38.53
[ Using the formulas for the above example ]
- 24 -
Adjacent Element
(Endfire Cell)
Quarter-Wavelength
Physical Spacing in
Feet (x 2)
38.53
38.53 x 0.83 = 31.98 ]
Delay Line
Physical
Length in
Feet
(0.83 VF)
31.98