Studying the schematics I noticed a front-end filter, that should be operating in the range of 60MHz - 200MHz. I studied the filter with a program and noticed, that the passband was 60MHz - 140MHz !! The upper end was blocked out.
I changed the circuit in a way that enables the radio to work as advertised by removing Capacitors C53 and C153. Now the filters upper edge is around 230MHz.
This modification doesn't affect 2m RX in anyway, because 2m has its' own, thight front-end, that is used instead of the modified filter, when in 2m band. HF and 6m aren't affected either.
The Capacitors are found in the PA UNIT board, behind the external speaker connector in a relatively easy place.
The job requires cautiousness because the components dislike static and excessive heat.
This modification works fine if you haven't done the Yellow Wire RX Modification.
At Least My unit worked well with this modification.
| Measured from my IC-706: | |
|---|---|
| Frequency | Sensitivity (microvolts /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 |
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