Improving the sensitivity of IC-706 to VHF

The IC-706MKI has absolutely insufficient sensitivity to VHF outside the 2m band. This is caused by an inappropriate range filter 60 – 200 MHz. In the zone 144 – 148 MHz, another filter is connected, there the sensitivity is sufficient. You know it anyway, that when you crash while debugging under 144, or above 148 MHz, the noise from the transceiver will change.

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

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?

• Disconnect the TCVR from all cables and place the top cover down
• we unscrew the base of the screws holding the lower cover
• on the PA board, locate the SMD coil L49 according to the picture (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 edit because of that, that I wanted to use a 70cm transverter with the IC-706. Downlink satellite frequencies come out after conversion above 148 MHz and I can confirm, that before the adjustment the sensitivity was lousy. After editing, it is noticeably better. Another modification is described at: .: MODS.DK :.

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

Frequency	Sensitivity (uV /12dB SINAD)
60-140	0.14
144-148	0.12
150	0.18
155	0.15
160	0.2
165	0.3
170	0.4
175	0.6
180	1.5
190	>100mV – deaf!
195	5
200	29

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