MODS FOR THE ICOM 706 - PART 3
The receiver sensitivity above 120MHz (except the band between 144-
148MHz) is very poor and also the transmitted FM deviation for NARROW
FM is too small; therefore I did some tests and came to the following 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 resistor R272 from 1K to 8K2. (at the bottom side of the
MAIN UNIT), then the max. deviation during transmitting 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 - 144MHz 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(82nH) 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
Now the sensitivity is good up to about 175MHz. Also the sensitivity in the
airband 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!
If you have other modification info, please let me know.
As I do not have packed, you can send info via Bart, PA0BJK:
My Fax nr. (at QRL) is:
+31 24 3533509, Frank Bremer, building M1034.
My home address: Zwanenveld 3041, 6538ZW Nijmegen, the Netherlands.
best 73, Frank PA0FBK
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