MODS FOR THE ICOM 706 - PART 5
The reciever sensitivity above 120 MHZ ( except the band between 144
to 148 MHZ ) is very poor and also the trqnsmitted FM deviation for NARROW
FM is too small; therefore I did some tests and came to the followinf two
To carry out these modifications it is necessary to use the IC706 service
manual, which can be bought at any ICOM dealer.
1. When choosing NARROW at FM, then during transmitting the max deviation
is reduced from 4.8khz to 2.4khz. It is still desirable to choose
NARROW at FM because the receive performance is better then.
After changing resister R272 from 1K to 8K2 (at the bottom side of the
main unit),then the max. deviation during transmit goes from 4.8khz
to 4.3khz when choosing NARROW at FM.
The modulation at AM is also changed now, but this can be corrected
with potmeter R271.
2. To improve the receiver sensitivity between 120 - 144 MHZ and between
148 - 200MHZ the following modifications can be carried out.
At the PA UNIT change the 60 - 200MHZ bandpass:
a)Remove C53(20p),C152(20p),C153(12p) and C154(20p).
b)Short-circuit L49(83nH) by soldering an interconnection at the place
of the removed C153
c)The inductance of L16,L17,L18 and L19 must be reduced somewhat.
This can be done by separating the windings somewhat with a small
Now the sensitivity is good up to about 175MHZ. Also the sensitivity in the
air band is much better now.
For receiving above 175MHZ the low-pass filters at the ANT2 input have to
be changed (components around L16,L17,L18,L19) I would not recommend that,
because the spurious suppression during 2M transmitting becomes worse then!
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