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Active Tuning Antenna System
Installation/Operating Instructions
Thank you for choosing Yaesu's exciting new ATAS-25 Active Tuning Antenna System. We hope and trust that you will enjoy many
years of enjoyable field operation with the ATAS-25!
The ATAS-25 utilizes a manual tuning system which resonates the radiating element for lowest SWR without the need for expen-
sive, inconvenient mono-band resonating whip assemblies. The ATAS-25 allows dual-frequency operation (on HF or 50 MHz and
either 144 or 430 MHz), if two transceivers are combined via a suitable diplexer (not supplied). The ATAS-25 is designed to mount
directly onto a standard camera tripod (not supplied); see Figure 1.
I
NSTALLATION
1. Mount the ATAS-25 main body onto the tripod.
2. Referring to Figure 2 and the following chart, connect the
radiating elements according to the operating band, then
screw the radiating element securely to the top of the coil
assembly of the ATAS-25.
(
)
O
B
R
E
PERATING
AND
ADIATING
LEMENT
S
7 MHz
Three Elements
14 MHz
Three or Two Elements
21 MHz
Two Elements
Two or One Element ( s ) , or No Connection
28 MHz
50 MHz
Do Not Connect
144 MHz
Not Used
430 MHz
Not Used
NOTE: When the ATAS-25 is fitted with two radiating
elements, use the top radiating element (the one with
the rubber cap) and the bottom radiating element (the
one with the threaded adapter at the bottom). When the
ATAS-25 is fitted with only one radiating element, move
the threaded adapter to the bottom of the element with
the rubber cap, then screw that element onto the top of
the coil assembly (Figure 3).
3. Secure the V/UHF radial elements to the bottom of the ATAS-
25 main body, using the supplied Allen wrench (Figure 4).
4. Connect the supplied radial wires to the bottom of the ATAS-
25 main body, then extend them outward from the antenna
base (Figure 5).
5. Connect the coaxial cable from the transceiver's HF an-
tenna jack (see Figure 6). Typically, you can use the built-
in SWR meter in the transceiver, but alternatively you
may adjust the SWR using an "Antenna Analyzer" prior
to connecting the coaxial cable to your transceiver.
If you operate the ATAS-25 along with the FT-817ND, we recom-
mend that you set the transceiver's Menu #07 (ANTENNA) to "REAR"
for all bands (HF/50/144/430 MHz), to pass all bands' RF power to
the rear antenna jack of the FT-817ND. Refer to the FT-817ND
operating manual for details regarding the Menu selections.
For operation on the 144 and 430 MHz bands, in addition to
HF/50 MHz using the FT-847/-100/-100D/-857D/-897D, you
may wish to consider the purchase of a "Diplexer" (for the FT-
100/-100D/-857D/-897D) or "Triplexer" (for the FT-847) device
to contact to the appropriate transceiver's antenna jack; the
Diplexer or Triplexer will then automatically pass RF power
from the band in use while isolating the other one or two jacks.
If you do not have a Diplexer or Triplexer, the coaxial cable
connector from the ATAS-25 will have to be moved manually to
E
A
C
8
2
X
7
0
1
ATAS-25
the appropriate antenna jack when you wish to operate on
VHF or UHF.
While operation is not guaranteed on the 10/18/24 MHz bands,
please feel free to experiment on these bands, as low SWR and
good efficiency will be obtained in many instances.
Figure 1
Figure 2
Figure 3
Figure 5
O
PERATION
1. Tune the transceiver to the desired operating frequency.
2. Referring to Figure 7, raise and lower the coil assembly
while listening to the band noise, and seek the position of
the coil assembly producing the most noise in the re-
ceiver. If a peak in the sensitivity is not obtained when the
coil assembly is fully retracted to the lowest (shortest)
position, remove one radiating element from the coil as-
sembly and try again. You may have a total antenna length
that is too long.
3. Key the transmitter in the CW mode, and check the SWR
meter reading.
4. Referring to Figure 7 again, carefully turn the coil assem-
bly to the right or to the left while the transceiver is receiv-
ing. After making an adjustment, stand away from the an-
tenna and check the SWR again, and repeat (or reverse)
the procedure until the best SWR is obtained. Do not touch
the coil assembly during a transmitting session.
5. If low SWR on an HF band cannot be satisfactorily ob-
tained, connect (add) the supplied spare radial wire to the
bottom of the ATAS-25 main body and extend it outward
from the antenna base, then try the above procedures
again.
Coarse Tuning
U
C
SE OF
APACITOR
If it is not possible to achieve a low SWR on
the 144 MHz band, pass the supplied "Capaci-
tor Tube" onto the VHF radial element, then slide
the Capacitor Tube outward, starting at the in-
nermost position, so as to obtain the best
SWR. When the optimum position is identified,
secure the Capacitor Tube to the radial element
using the supplied Allen wrench.
Slide the Capacitor Tube outward from
inner end to Position yielding best SWR.
VHF Radial Element
Figure 4
S
PECIFICATIONS
Frequency Range: 7/14/21/28/50/144/430 MHz
Input Impedance: 50 Ohms
Max. Input Power: HF/50 MHz:100 W (SSB/CW, 50% Duty)
Matched SWR:
Height (Approx.):
Weight (Approx.): 2.05 lb. (930 g)
Figure 6
C
AUTIONS
The ATAS-25 is designed for temporary field operation.
We do not recommend that the ATAS-25 be used for per-
manent operation, as it does not include the weather-
proofing needed for long-term outdoor installation.
The ATAS-25 is designed for a maximum power of 100
Watts (SSB/CW) or 50 Watts (AM/FM, 144 MHz, 430
MHz). Do not exceed this combined power input (if two
transmitters are connected via a diplexer) when operating
the ATAS-25.
Do not connect (mount) the ATAS-25 to the antenna jack
of the transceiver or antenna mount directly using a double-
male coaxial adapter plug. The ATAS-25 must be mounted
onto a tripod or other similar item using the Camera Screw
hole (Type "U¼") on the bottom of the ATAS-25 main body.
Do not allow anyone to touch the radiating element during
a transmitting session, due to the danger of burning of the
skin caused by the high RF voltage present. It helps the
accuracy of the SWR measurements if all people are stand-
ing at least 10 feet (3 m) away from the radiating element,
anyway, to minimize inaccuracies due to mutual coupling
to the human figure(s) in the vicinity.
If erratic transceiver operation is observed, there may be
common-mode current flowing on the shield of the coaxial
cable. Make an RF choke by coiling about eight turns of
Fine Tuning
cable into a coil of diameter approximately 6" (roughly 150
mm) near the ATAS-25, taping the coils to hold them in
place. If this does not eliminate the problem, reverse the
coax ends, placing the coil near the transceiver. If addi-
tional cable is available, place a coil at both ends of the
coaxial cable in difficult cases.
Set up the tripod as low and level as possible, for maxi-
Figure 7
mum stability of the tripod/antenna assembly. SWR tends
to be best with the base of the ATAS-25 near the ground,
T
UBE
as well (Figure 1).
Should the ATAS-25 get wet due to rain, wipe off the antenna's
components using a dry cloth, then completely dry the ATAS-
25 overnight with the coil assembly fully extended.
For SSB/CW DX operation on the 144/430 MHz bands,
remember that the convention for polarization in most ar-
eas is horizontal, not vertical, so we recommend the ATAS-
25 mostly for local FM work on those bands.
Make every effort to install the ATAS-25 away from areas
where people might trip over the tripod legs, coaxial cable,
or counterpoise wires. We strongly recommend that the
tripod legs be staked firmly to the ground, or the tripod and
antenna be otherwise secured with guy ropes and stakes,
to prevent the antenna from accidentally tipping over, so
as to avoid injury to bystanders and/or damage to an-
Secure the Capacitor Tube using
tenna components.
the supplied Allen Wrench.
S
UPPLIED
ATAS-25 Main Body ............................................................. 1
Radiating Elements .............................................................. 3
Amateur Bands
Radial Element (for VHF band) ........................................... 1
Radial Element (for UHF band) ........................................... 1
Radial Wires (20 ft (6 m) , 9.8 ft (3 m) & 6.6 ft (2 m) Length) ........... 1
50 W (AM/FM)
Spare Radial Wire (32.8 ft (10 m) Length) .......................... 1
144/430 MHz:50 W (ALL MODE)
Capacitor Tube ..................................................................... 1
Less than 2.0:1
Allen Wrench ........................................................................ 1
Max. 7.2 ft (2.2 m) during Operation
Operating Manual ................................................................. 1
Min. 1.96 ft (0.6 m) for Transporting
I
TEMS
YAESU MUSEN CO., LTD.
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Summary of Contents for Yaesu ATAS-25
- Page 1 ATAS-25. either 144 or 430 MHz), if two transceivers are combined via a suitable diplexer (not supplied). The ATAS-25 is designed to mount Do not connect (mount) the ATAS-25 to the antenna jack 3. Key the transmitter in the CW mode, and check the SWR directly onto a standard camera tripod (not supplied);...