- WARNING
-
Installation of this product near power lines
is dangerous. For your safety, follow the
installation directions.
General Description
The TH3jr antenna was designed for the Ham
who has space limitations but still wants top performance
on 10, 15 and 20 meters.
The TH3jr is constructed of taper-swaged
aluminum tubing which offers low wind resistance.
It can be rotated with a heavy-duty TV
rotator. The light weight is ideal for rooftop or
lightweight tower installations. The antenna features
super strength stainless steel hardware and a
boom-to-mast bracket that will fit masts up to 2
inches in diameter.
Specifications
Electrical |
Forward Gain | Up to 8 dBi |
Front-To-Back Ratio | 25 dB |
VSWR at Resonance | Less than 1.5:1 |
Nominal Impedance | 50 ohms |
Power Capability (Transmitter Output) | 600 Watt PEP, 300 Watt AM |
Lightning Protection | DC ground |
Mechanical |
Net Weight | 21 lbs. (11.7 kg) |
Boom Length | 12 ft. (3.65 m) |
Longest Element | 27�3" (8.30m) |
Turning Radius | 14�9" (4.49m) |
Wind Survival | 80 mph (128 kmph) |
Accepts Mast | 1 �" to 2" (32 mm to 51mm) |
Surface Area | 3.35 sq. ft. (0.32 sq. m) |
Effective Moment* | 310 ft. lb. (53 kg-m) |
Wind Load at 80 MPH | 87 lbs. (39.4 kg) |
Hardware | Stainless Steel (except for U-Bolts and some small parts) original hardware was NOT Stainless |
Suitable Rotators | Hy-Gain AR-40 or CD-45II |
*Effective Moment is defined as the product of the antenna weight and turning radius.
Step-By-Step Assembly
- NOTE:
- When unpacking your antenna, check
the inside of all tubing for parts (clamps, insulators,
smaller tubing, etc.). To conserve
space during packing, these smaller articles are
put inside large pieces.
Select the two boom sections (1 1/4" x 72")
and boom-to-mast brackets.
- NOTE:
- The reflector portion of the boom has
holes drilled in it for the beta match. Make sure
they are on top when you tighten the boom-to mast
bracket. See illustration in this manual.
Assemble the two halves of the boom-to-mast
bracket by placing the 1/4" x 3/4" screws in the
four outside holes as shown in Figure 1.
DO
NOT tighten at this time.
Slip the boom sections into the boom-to-mast
bracket until they meet in the middle. Make
certain the drilled holes on the reflector end are
on top and close to the boom-to-mast bracket,
then tighten the bolts securely.
Place a 11/4" caplug on each end of the boom.
Insert the two U-bolts into the boom-to-mast
bracket and start the 5/16" nuts and
lockwashers.
DO NOT tighten at this time.
Start at the reflector end (boom section that has
the hole drilled in it) and measure approximately
1" from the end of the boom and install the
element-to-boom bracket as shown in Figure 2. Only
tighten the hardware enough to keep the bracket
in place. Final positioning of this element will
depend upon placement of the driven element and
the dimensions from Figure 4.
Select the Rl sections (7/8" x 72") of tubing and
slip one end of each in each side of the bracket
and tighten the bracket securely with the
exception of the two anchor screws.
DO NOT
tighten at this time.
Measure along the boom 65 1/8" from the center
of the reflector element-to-boom bracket and install
the driven element-to-boom bracket. Select
the DE sections and slip the driven element insulators
onto one end of the DE1 sections (7/8" x
72").
Slip the insulated end of the DE1 section into the
driven element bracket and tighten securely. See
Figure 3 for proper installation.
DO NOT tighten
the anchor screws at this time.
Measure 74" from the center of the driven element
bracket to the center of the director and install the
director element-to-boom bracket. Select and install
the D1 sections (7/8" x 72") by slipping one
into each side of the bracket and tighten securely.
DO NOT tighten the anchor screws at this time.
Now recheck the measurement and make certain
all the elements are aligned evenly.
- NOTE:
- At this time select your mode of transmission
- either Phone or Continuous Wave (CW).
Refer to the dimensions for your mode of transmission.
Use the same mode for all dimensions.
Since this was written in the 1970s, changes in band allocations
have moved the phone segment lower in frequency. The best DX and contest settings
would now be the ones for CW. The phone settings are higher in the band. Some experimentation may be necessary.
Select the 10-meter reflector trap (marked REF)
and a #6 tubing clamp and slip it on the end of Rl.
Slip the longest end of the 10-meter trap into the
Rl section to the dimensions given for your mode
of transmission. Tighten the tubing clamp slightly.
See Figure 5.
Select R2 (3/4" x 10 1/2") and slip it onto the 10-
meter trap assembly. Slip one #6 tubing clamp on
each end of R2. Tighten slightly.
Select the R3 sections (7/16" x 32") and slip it
into the 15-meter trap assembly to the
dimensions shown for your mode of
transmission. Slip on #6 tubing clamp, and
tighten slightly.
Place a 7/16" caplug on each end of the
element.
- NOTE:
- The remaining elements will be
installed in the same manner as above with the
exception of using the trap designated for that
particular element.
The traps are marked as
follows:
- 10-Meter Traps -
- Director - 10 DIR
- Driven Element - 10 DE
- Reflector - 10 REF
- 15-Meter Traps -
- Director - 15 DIR/REF
- Driven Element - 15 DE
- Reflector - 15 DIR/REF
Select the remaining DE tube sections and
install as before.
Select the remaining director tube sections and
install as before.
Select the beta match tombstone support insulators as
shown in Figure 7.
Select the beta shorting strap and install as
shown in Figure 7. Tighten all hardware used
with the beta match, shorting strap and driven
element. Remeasure the dimensions between
elements as shown in Figure 4. Tighten all
hardware including the anchor screws at this
time.
A balun is not required for normal operation of
this antenna. However, there are three recommended
feedpoint configurations, one of which
utilizes the Hy-Gain Model BN-86 balun for
increased performance and convenience.
The first feedline configuration involves connection
of the coaxial feedline directly to the driven
element. The recommended feedline is RG-213/U
(such as Belden 8267). Other types of coaxial
cable may be used if proper selection and careful
assembly are utilized. The feedline should be
stripped as shown in Figure 7. Attach solder lugs
(not supplied) to the center conductor and shield
for easy connection to the driven element.
Weatherproof all connections.
The second feedpoint configuration involves construction
and installation of a homemade RF
choke. The RF choke will prevent RF from flowing
on the outside of the coaxial shield. This will
block radiation from the coaxial feedline; thereby
reducing the risk of TV1 and preventing radiation
pattern degradation.
The third feedpoint configuration involves using
a 50 ohm 1:1 balun to connect the feedline to the
driven element. (Hy-Gain Model BN-86 is
recommended.) A balun will act as an RF choke
and will balance the flow of current on the driven
element, resulting in a symmetrical radiation pattern.
A balun will also have a coaxial connector,
providing more convenience than a coax splice.
Follow the instructions supplied with the balun
for connection to the antenna.
- NOTE:
- Use caution when selecting a balun to use
with this antenna. Some baluns are designed for
50-75 ohm impedance and may result in a higher
SWR when used with this antenna. For best
results, use the Hy-Gain BN-86, 50 ohm balun.
The Model BN-86 is available at your local Hy-Gain dealer.
- The original balun used with this model of the TH3jr
was Hy-Gain BN-12. If you use the BN-12 and want maximum front-to-back ratio
change the "A" dimension on the Driven Element to 10" for Phone and 13 1/2" for CW.
Carefully recheck all measurements, make certain
the drain holes in the traps are facing down and
then tighten all compression clamps securely.
Make certain all electrical connections are tight.
Weatherproof your coaxial connection using
Coax-Seal (R) or some similar substance.
Slip the boom-to-mast clamp over your mast and
tighten securely.
This completes your installation.