For Improved f
hearing above 148Mhz for the ICOM IC-706:

Tools required:

1) #0 Philips head screwdriver
2) 10 - 15 watt pencil tip soldering iron
3) Magnifying glass
4) Tweezers

 Remove the TOP cover by removing three philips head screws on the top
and one on each side. The fourth yellow wire from the right on the header, 
should be cut open. just above the 9 MHz SSB filter FL-30. 
 This controls a low pass filter at 120MHz which remains 
in service when above 148MHz and make the IC-706 very deaf above 148MHz.
Note: Be careful, another yellow wire exists on the same header.

 Above is the new official Mod from Icom USA !!!
This increades sensitiivity avove 148MHz, but degrades 
sensititivity in the 88-108 FM Broadcast portion.
***************************************************************************
 Below is a mod that takes the yellow wire mod one step further, to
restore FM broadcast sensitivity and keep reception above 148MHz.
Connecting open yellow wire to J8 VCO transistor switch bank.
 I tried this mod and it works, If I just did the yellow wire mod, I noted 
RF images from the 144-148MHz, falling in the 82-84MHz region, by reconnecting
it to the VCO switch bank, no more images, and FM broadcat restored, with good
sensitivity above 148MHz. Only noted that FM broadcast FM band can overload
aircraft band betwwen 118-129Mhz, I switch the preamp off(green to black) and 
the problem goes away and still can hear aircraft.
 
73
Mike
WB6DJI

I suggest that a pin with a plug be done for this J8 mod for future Icom 706's
radios to implement this in a production environment.

Date: 16 Nov 95 15:12:30 EET
From: harjula@ntc01.tele.nokia.fi
Subject: Icom 706 - modified

In article <4884r9$14to@chnews.ch.intel.com>, cmoore@vegas.ch.intel.com (Cecil A. Moore~) writes:
> In article <1995Nov8.090310.1@ntc01.tele.nokia.fi>,
>  <harjula@ntc01.tele.nokia.fi> wrote:
>
>>The fourth yellow wire seems to control
>>a lowpass/highpass 120 MHz filter. In the standard configuration the highpass
>>filter is used only on 144-148 MHz, every other frequency uses the lowpass.
>>Anyway, if you want to listen to frequencies above 120 MHz this mod is
>>very useful. It does even remove most of the FM band intermodulation.
>>I just don't understand why Icom has not put the switching limit on
>>120 MHz instead of 144/148.
>
> Does this mod affect HF or 6m? After the mod, what frequencies use the LP and
> what frequencies use the HP filter?

The mod affects only frequencies above 60 MHz. If you just cut or remove the
yellow wire, the HP or actually 2m bandpass filter is used all the time.

Last night I took the loose yellow wire and connected it to a VCO control
switch transistor (?) on the lower PC board. Now I have the LP filter in
use between 60 and 129 MHz and the 2m bandpass between 129 and 200 MHz.

There are five SMD transistors on the lower PC board just behind the
"MENU" button. The one in the middle controls the VCO that is in use
from 60 to 129 MHz. The single pin has 5V when within this range.

The mod affects only frequencies above 60 MHz. If you just cut or remove the
yellow wire, the HP or actually 2m bandpass filter is used all the time.
 
Last night I took the loose yellow wire and connected it to a VCO control
switch transistor (?) on the lower PC board. Now I have the LP filter in
use between 60 and 129 MHz and the 2m bandpass between 129 and 200 MHz.
 
There are five SMD transistors on the lower PC board just behind the
"MENU" button. The one in the middle controls the VCO that is in use
from 60 to 129 MHz. The single pin has 5V when within this range.
There is a trace from this pin to a plated-through hole near J8.
This is a good place to connect the wire. (I haven't even seen the
schematic so cannot say if this is the best way to do it.
But it works for me.) 
*****************************************************************************
(Notes: de WB6DJI) found this point with a DVM to identify right plated
thru hole(Just to to left of J8 marking on board on bottom side of radio)
I put a 3/8" wire, reheated it and got it to say in 
in the plated thru hole next to J8, the attached the open ended yellow wire to 
it. Careful not to damage the gray cable with your soldering iron, its pretty 
tight, small area in there!!
**************************************************************************** 
129 MHz seems to be quite close to the cross-over point of the LP and
2m BP filters. Here is a listing of the (NBFM) signal strength needed
to "light" the first segment on the S-meter on each frequency:
 
MHz     uV/LP     uV/BP
125     .8        2
135     12        .5
145               .15
155     30        .5
165               3
175               11
185               140
 
After the mod I can listen to the Helsinki airport on 134 MHz but the
Meteo on 128.4 is still drowned in intermod from the FM BC band.
 
> thanks and 73, Cecil, KG7BK, OOTC  (not speaking for my employer)
Neither am I. Proceed at your own risk etc. And have more fun with the 706 !
 
73 de Arto, OH2BGN

--
Arto Harjula                      tel +358-0-5112 8308   fax +358-0-5112 8299
Nokia Telecommunications / PMR    arto.harjula@ntc.nokia.com
 
 




