Improving the sensitivity of the IC-706 to VHF

IC-706MKI has absolutely insufficient sensitivity to VHF outside the 2m band. This is caused by an inappropriate filter for the 60-200 MHz range. Another filter is connected in the 144-148 MHz band, the sensitivity is sufficient there. You can also tell that when tuning below 144 or above 148 MHz, the noise from the transceiver changes.

If you are also interested in non-radio amateur frequencies on VHF (FM radio, aerial band, reception of weather satellites and others), a relatively simple adjustment is possible.

Analysis of IC-706

Pictured is part of the IC-706 schematic. The low-pass filter is designed with a very low cutoff frequency. This significantly reduces the sensitivity at higher frequencies. It can also be seen on the graph:

How to improve the sensitivity of the IC-706MKI

I found several solutions to the mentioned problem on the Internet, but I consider the OH6LGM solution to be the most suitable. It consists in the tripping of capacitors C53 and C153.

How to do it?

• TCVR disconnect from all cables and place the top cover down
• we unscrew the base of the screws holding the lower cover
• locate on the PA board according to the picture SMD coil L49 (blue) and capacitors C153 and C53 (brown)
• carefully fly out capacitors C153 and C53
• we place the cover and screw it
• we will connect the cabling
• turn on the transceiver

I tried the modification because I wanted to use it with the IC-706 transverter to 70 cm. The downlink frequencies of the satellites come out above 148 MHz after the conversion and I can confirm that the sensitivity was poor before the adjustment. After editing, it is noticeably better. Another modification is described at: .: MODS.DK :.

The author measured these values ​​on his device after modification

Warning: the author is not responsible for the consequences. You make all adjustments at your own risk.