ACOM LS108 HF Log-periodic Antenna
Continue in the same manner until you install all the nine strap pairs crossing between the antenna elements
(straps actually zigzag). At the last element (number 10), place a plain washer on the bolts closest to the
boom. Smear some conductive paste on the two surfaces of the cable ring terminals (lugs) of the balun-
transformer.
Connect the terminals to the bolts using M5 lock washers and nuts but do not tighten for now -
see
Fig. 6 Balun Connection.
At this stage of the installation check, whether all the nuts holding the phase line are screwed in but still
loose.
CAUTION!
The nuts holding the phase line should be tightened when you have reinforced the boom against the sag
(refer to section
2.7 Boom Support Assembly).
Now insert a strap-insulating spacer at each crossing point of the straps as shown in
Fig
. 5 Phase-line
Straps Mounting
. Orient the strap spacer between the two straps as shown in the figure. Slide it along the
arrow shown in the figure until the straps engage the top and middle spacer slots.
2.5. Attachment of Coaxial Feed Line
Use coaxial cable with 50-Ohm characteristic impedance. Check whether your cable will withstand the power
you intend to use at the highest frequency (30 MHz). To make use of the maximum permissible power of
LS108, cable type RG213 or better is required.
Stripe one end of the cable and install a type PL259 plug connector (male UHF) according to the connector-
producer instructions for the appropriate cable type. Couple it to the balun-transformer SO239A jack
connector - see
Fig. 6 Balun Connection.
Protect the coaxial connection against moisture leak in the connectors as well as in the cable.
Leave some cable drip-loop (see
Fig. 1
LS108 - Appearance)
to eliminate any undue mechanical strain on
balun transformer. Fasten the cable along underside of boom using ties delivered with antenna. First lay two
ties at the nearest strap-insulating spacer (located between ELEMENT 10 and ELEMENT 9). Together with
the cable, fasten also the legs (skirts) on the two strap-spacer sides (see
Fig. 5 Phase-line straps
mounting).
Continue fastening the cable with two ties at each spacer until you reach the mast.
Now fasten also the strap-insulating spacers in the other part of the boom (although there is no cable there).
2.6. Boom to Mast Assembly
The mast bracket (boom to mast holding assembly) consists of a pair of metal brackets and four U-shaped
bolts. It is factory mounted on the boom. Project the way you will mount the mast on the tower structure so
that the antenna is installed at a distance of no more than 30cm (1 ft) above the support. The mast must
protrude at least 80 cm (2.6 ft) above the antenna. Mark the draft position for the bracket on the mast.
Install firmly the mast in a vertical position so that it can bear the weight of the whole antenna.
Please look at
Fig. 7 Boom to Mast Assembly.
Unscrew the nuts from the two unengaged U-shaped bolts
and remove the bolts. Bring the boom near the mast at the height marked for the bracket. Re-install the two
U-shaped bolts so that they embrace the mast as shown in the figure
.
Place the removed four lock washers
and nuts and fully tighten all 16 nuts of the holding bracket.
Fasten the coaxial feed line to the mast using two ties.
If you will use a rotator, leave a large enough loop of cable around the mast in order to allow at least 360
degrees free rotation of the antenna.
2.7. Boom Support Assembly
To reinforce the boom against sag, it is tied up to the mast top via guys. They consist of two legs of
stainless-steel cable with a turnbuckle each as shown in
Fig. 8 Boom Support Assembly.
On the mast top
is installed a drawing bracket which serves for guys support.
After the boom has been assembled to the mast, uncoil the two guys (factory mounted to the boom). Adjust
the two turnbuckles so they extend to their maximum length. Loosen the two U-shaped bolts and slide the
1mm=39.37mil 1cm=10mm=0.3937” 1m=100cm=3.281ft 1kg=2.205lbs 1m =10.764sq.ft
1km/h=0.62137mph
4
2
