Practical_Antenna_Handbook_0071639586

C h a p t e r 2 2 : R a d i o A s t r o n o m y A n t e n n a s 499
Unlike the sun, Jupiter does not often rise high in our sky. Its transit, as viewed at
midlatitudes in the northern hemisphere, is typically close to the horizon—rising in the
southeast and setting in the southwest. In that respect, Jupiter is an excellent target for
a typical HF Yagi or cubical quad whose height has been optimized for low elevation
angles. Also, Jupiter is visible (and audible) at times totally unrelated to our day and
night periods. As a result, there may be periods when Jupiter’s emissions may be difficult
to hear because the sun is also “in your face”. Search the Internet for detailed calendars
of Jupiter’s transits.
For monitoring Jupiter, a good beginning antenna can be a simple dipole cut for the
middle of the 18- to 24-MHz band, which happens to coincide with the 15-m amateur
radio band. The antenna should be installed in the normal manner for any dipole, except
that if it is fixed in one position the wire should run east-west in order to maximize
pickup from this southerly rising planet.
Figure 22.1 shows a broadband dipole that covers the entire frequency span of interest
(18 to 24 MHz) by paralleling three different dipoles: one cut for 18 MHz, one cut for
21 MHz, and one cut for 24 MHz. The dimensions are
A 19.5 ft 24 MHz
B 22.3 ft 21 MHz
C 26 ft 18 MHz
As discussed in the chapter on multiband wires (Chap. 8), there are several approaches
to making this type of antenna. One is to use three-conductor wire and cut the
wires to the lengths indicated here. Another is to use a homemade spacer to spread the
wires apart.
Figure 22.1 Wideband HF dipole for Jupiter reception.