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IC-718 Mods
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Extended TX and RX for IC-718
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The IC-718 #06 (Italy and other
Countries) can receive and
transmit ONLY on the Ham bands.
It is simple to get a complete
coverage (0.1 - 30 MHz) both in
reception and transmission, by
removing the three diodes D53,
D54 and D55.
Enjoy. |
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Some times ya just gotta wonder why they don't
do this at the factory. Works for all 706's, 718
and many other ICOM rigs. Here ya go, the manual
Tune controller that:
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Automaticly switches your rig to CW mode
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Automaticly turns power down to 10 watts
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Automaticly transmits CW CXR while tuning
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Automaticly returns to previous mode and
power setting when turned off.
A simple SPST can be mounted almost anywhere. I
mounted mine on a small "L" beacket held down by
top cover screw. a single 10 to 20 K ohm 1/4
watt resistor can be used. Just mount the switch
connect the wire per diagram. Enable rig for
AH-4 tuner. (?) (you may need to experment with
this setting.)
10k-20k ohm between pin 2 and 3, switch wired to
pin 1 and 4.
switch on = 10W CW CXR switch off= previous
mode/power
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D48 to D55 Role informations
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Hi,
I've tested some combination of D48 to
D55. I have found some interesting things
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D52 : If present, you change your IC-718 into a IC-78.
D50 : If not present, the 160 meters band is reduced.
D54 : Full band TX (1.6 to 30 or 33 MHz (depend on D55).
D55 : if not present, extend range from 30 up to 33 MHz.
Some combinations :
equivalent to #06 if:
D48 ON
D49 OFF
D50 ON
D51 OFF
D52 OFF
D53 ON
D54 ON
D55 ON
equivalent to #04 if:
D48 ON
D49 OFF
D50 ON
D51 ON
D52 OFF
D53 ON
D54 ON
D55 ON
equivalent to #03 if:
D48 ON
D49 OFF
D50 OFF
D51 OFF
D52 OFF
D53 ON
D54 ON
D55 ON
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Balancing the first RX-mixer of the receiver
(MAIN UNIT board
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ICOM
transceiver IC-718 has an excellent receiver in
spite of its low price. I can say that this
device works better on low bands (40/80/160 m)
after modification!. The receiving part (before
the second RF-mixer) is completely same as in
Kenwood TS-570D, but it has lower noise level in
comparison with Kenwood.
I checked transceiver in PACKET, AMTOR, PACKTOR-I,
CW, PSK-modes with KAMplus. Switching speed
(TX/RX) for AMTOR is more than sufficient. For
detailed characteristics look on site ICOM. I
want to thank Vladimir - RK6FX for his ideas. So
let's begin.
Remote top and bottom covers and turn
transceiver over.
Swith on transceiver and turn the frequency to
100 kHz.
Connect RF-voltmeter to pin 12 of ACC-connector
for TNC and adjust resistor R1104 until the
minimum level of voltmeter scale. This resistor
is located inside a soldered box on the board. |
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Decreasing of superfluous amp in second
IF-stage, (MAIN UNIT board
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Remote top and bottom covers and turn
transceiver over.
Tune for any weak SSB station in 3.6 MHz.
Adjust resistor R1614 for the best signal/noise
ratio. |
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Better original mike audio MH-36, IC-718 and
other
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If
you look inside the stock hand mic there is a
thick felt plug, about the size of a small
aspirin tablet, in the front of the electret
element. It is a very dense material, unlike
plastic foam, and the one in my mic is almost
1/4" thick!
I thought that this must surely restrict middle
to high audio frequencies so I removed it and
replaced it with a small piece of open cell
foam. |
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Open the bottom and at back, there is the main
board. At the right bottom is the option for the
filters. Close to it - is R1707. This adjust the
TX Power. Next to it is R1730. This adjusts the
AM carrier.
Adjust R1707 for what you want up to about 200
watts. It will give more but that is at
saturation point of the device. Adjust R1730 for
the AM carrier for about 40 or 50 watts only.
This mod is only in testing and I cannot stress
more to be carefull and keep it COOL. |
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you want to disable the agc completely where it
would be "Off" and the receiver at full gain,
you can try cutting the trace from R1815 (22k)
from Q1805. This resistor is in the base lead to
transistor Q18, which is the AGC amplifier. With
this resistor opened, no voltage from the AGC
rectifier diodes can reach Q18 so it never
attempts to lower the gain of the receiver.
My R7000 has nearly identical agc circuit and I
did this modification and it works very well. I
have not tried it on my IC-718.
If you want a "slower" agc for ssb, it will not
be solved by simply adding more capacitance for
C 1803. The high value of R1808 will keep it
from charging or discharging rapidly. That's why
you see so little difference between agc action
on CW and SSB. The simplest solution that would
require very few parts changes would be to turn
the AGC into a "hang" type with a FET.
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The
AGC of this rig on SSB seems to be too fast, but
on AM it is considerably slower. SSB uses medium
speed, while AM uses medium and slow speed
together. This problem is easily cured by
connecting slow and medium time delays in
parallel, when AM time delay is used on SSB. CW
and RTTY remain still original fast delay.
Open bottom cover and find R1807 and R1808 on
top side of main board near J2602 (DSP AF
connector). Connect their ends (connected toward
to sw transistors), together with small jumper
(arrow) and that's it.
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Modify IC-718#04 to IC-718#03
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How
to change freqency coverage from version
IC-718#04 to IC-718#03?
It is easy to restrict the freqency range (to
modify from #04 to #03)
Remove D50 diode in the Logic board is enough.
D50 is located close to D54. |
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Remove D-54 on the logic board, located behind
the front panel.
D-54 is located in the upper left corner in the
lower vertical group of diodes.
X
X
X
X
X
X
0-D54
X
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ATTENTION
The KB2LJJ takes no responsibility for any damage during the modification or for
any wrong information made on this modification.
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