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Length
240
Frequency(MHz)
Above Ground Installation
If the HF2V is to be mounted some distance above the earth a
resonant
radial ground system will most likely
be necessary for low SWR and efficient operation. The length in feet of radial wires for any band can be
found from the formula:
At least two radials per band should be used if at all possible for the sake of efficiency, although operation
with a reasonably low SWR may be possible with only a single radial per band. If only two radials are used
per band these should run at 180 degrees to each other. Resonant radials should be connected to the braid
side of the coax at the feedline terminals and insulated at the far end. Resonant radials need not remain
parallel to the earth, and a fair amount of slope will not significantly affect SWR or performance. If,
however, resonant radials are not sufficiently elevated, the earth below them can cause them to resonate at a
much lower frequency than expected, and their length may have to be trimmed considerably to restore the
overall system (vertical radiator and radials) to resonance for low SWR operation without having to resort to
a trans match at the input end of the feedline.
If the antenna is to be mounted
above ground
it is recommended that one set of
short
guys be attached to
the antenna at a point that is approximately 1/3 of the way up from the feedpoint. These guys will help to
steady the lower sections and to prevent the wind loading on the upper sections of the tubing. Four guys will
offer more support than three, and unusually long guys should be avoided. Under no circumstances should
guys be placed on the upper section of an antenna. The light tubing used in the upper half of the antenna is
capable of supporting itself in very high winds, but it cannot support itself and guy lines that will themselves
will be subject to wind and perhaps ice loading.
Guys should be made of non-stretch non-conductive material such as monofilament fishing line in the larger
sizes. Light nylon twine should be avoided regardless of its strength rating because it can stretch as much as
15%. Polypropylene rope or even nylon rope may also be used, although the former should be checked
periodically for signs of weather deterioration.
The wire suggested for elevated radials is a 14 gage stranded copper with a black relaxed PVC insulation.
The relaxed insulation makes handling the wire easy since it will not kink or act like a spring. The PVC-
insulated stranded copper radial wires are UV-resistant and roll out easily, unlike the wire that is commonly
available at "big-box" stores.
Optional Accessories for the HF2V and Notes on Top Loading
In its basic configuration the HF2V stands 32 feet tall and thus operates as a quarter-wave vertical on 40
meters with reasonably good efficiency over fair to good ground system.
On 80 meters, however, this height represents something of a compromise compared to a full quarter-wave
vertical antenna for this band. One simple way to approach the performance of a full size vertical on 80
meters is to attach top-loading wires near or at the top of the antenna in order to simulate a much taller
physical structure. Maximum loading will occur when the wires are extended parallel to the earth, but that
arrangement would call for additional supports that are nearly as tall as the antenna itself. The "umbrella"
system shown will conserve space and resources in that the support lines to the top loading wires may be
placed at ground level.
The angle of slope for each wire is not especially critical, but 45 degrees represents a good compromise
between loading and space conservation. Fewer than four wires may be used, although in such a case it may
be expected that three wires of given length will provide less loading than four wires of the same length.
It is obvious that the addition of top-loading wires to the HF2V will call for less inductance in the 80 and 40
meter tuning circuits, in which case the shorting strap for the 80 meter circuit will be needed. Unfortunately,
there is a limit to the amount of top loading that may be used with the HF2V before 40 meter operation is
adversely affected. Four "umbrella" wires each attached to the antenna at the junction of tubes (K) and (L)
