Simple all HF Band matching device The Universal ATU that is described hereinabove is
simple but has lots parts and sometimes is not so obviously in tuning.
However it is possible make a simple all band ATU that is clear
in tuning and has small quantity of parts. The schematic of simple
ATU is shown in Figure 12. However the simple ATU is not so effective
on the high HF bands (compare to the previous ones). As can be seen
from the diagram, this ATU is a conventional LC-tuned tank. With
switch S3 and capacitor C1, it can be tuned on frequency of any
selected amateur band. Switch S1 allows adjustable coupling with
the transmitter's final stage. S2 provides the variable coupling
to the antenna. By using S1, S2, S3, one may match just about any
transmitter's final amplifier to any antenna. The matching network
works well in the HF range from 1.8 to 30 MHz with nearly all antennas.
But, I should repeat, in the higher ranges above 14 MHz to 32 MHz,
the efficiency is low.
For the coil form for L1, I used a glass jar (it was
empty jar from mustard) with an OD of 55 mm and a metal screw-on
lid.
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L1 consists of 30 turns of copper wire with a diameter
of 1.5 mm, (#14AWG). The coil was wound over a 50-mm length on the
jar. The first and last turns were held in place by using automobile
epoxy. The first, second, and third taps were placed at 2, 3 and
4 turns. Then the next turns 3, 4, and 5 were placed at 6, 8 and
10 turns. Taps 6 and 7 are at 13 and 15 turns. Then the turns are
uniform for four turns. Then, tap 8 is at 19 turns, tap 9 at 23
turns, tap 10 is at turn 27 and tap 11 is at end of the coil- 30s
turn. Capacitor C1 is a two section air variable capacitor from
an old tube broadcast receiver. Such kind of capacitor may be used
at power up to 100 watts going to this ATU. The ATU also improves
reception because selectivity of the LC- circuit.
To tune
the ATU, an LED D1 is used. The ATU is tuned for maximum brilliance
from the LED. The LED is located in the winding of the current
transformer T1. The current transformer is wound on a ceramic
ring with the OD of 22 mm. I used a ceramic ring from an old tube
socket. All the leads and center metal clamp was removed. Another
type of ring (ceramic, plastic or ferrite) for the current transformer
may be used everything is depend on the scratch box and experience
of amateur.
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