This text deals with ICOM's Mobile radio IC2340H. On some of icom dual band
mobile transceivers there is an RF attenuator which attenuates the received
signal by 20dB. In my opinion this is a great feature especially when you
operate in cities or in area's with lot of RF signals, repeater, etc.
The attenuator function reduce the intermodulations that appears while
receiving in those areas, and let you listen more quietly on your favorite
channel, when you listen to a local repeater you can hardly feel the 20dB
attenuator, but the intermodulations almost disappear.
The problem is that the attenuator was featured on old icom mobile rigs
(such as IC2340H, IC3230H), but not on the IC2340H. The next lines will
guide you how to add this feature. All you need is 2 1p2t small switch,
and 2 12Kohms resistors.
VHF MODIFICATION
-
Open the upper cover of the transceiver.
-
Locate D9 on the print (left to the Power Amplifier while looking from the
front of the transceiver)
-
Solder a 12K resistor to the anode of D9 as close as possible to the diode,
(with no wire, the pin of the resistor should be soldered to the pin
of the diode)
-
The other side of the resistor should be wired to the small switch
(the switch can be mounted on the back of the transceiver, there's an hole
in the heatsink which you can use to insert the wires to the transceiver.
-
The other side of the switch should be tied to 5V
(you can find a 5V terminal at J2 pin 2, j2 & j1 located near the VCO
at the front of the print it is a 2*4pin sip connector, j2 is closer
to the VCO.
UHF MODIFICATION
-
Open the lower cover of the transceiver.
-
Locate D17 on the board (this diode is wired under the board, just beside
L22. there are 2 holes, I am talking about the one located closer to the
antenna)
-
Solder another 12K resistor in the same way it was done in the vhf to
the anode of D17 just under the print ( the anode is the left pin of
the diode ,the pin which located closer to the power amplifier.
-
The other side of the resistor should be wired to the other small switch...
-
The other side of the switch should be tied to 5V
(for example to the right pin of the regulator IC7)
Explanation
When you turn this switch on, it turns the diodes on, and attenuates the
received signal.
This modification was tested, but you will do it on your own risk.
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