IC-746 FAQ
Most hams feel that raising the RF output power above 100w is a bad idea for a variety of
reasons:
•
You can exceed the power ratings on the output transistors. Even if they don't blow out
right away, they can eventually due to the long-term electrical and thermal strain.
There's nothing to prevent you from frying the rig except luck. There have been reports
of output levels as high as 180w; nearly 30% above the published ratings.
•
Pushing the PA transistors closer to saturation moves them toward non-linear operation;
thus increasing IMD and splatter. Much of the "extra" power can end up as interference
instead of in your signal.
Some IC-756 owners have found this out first hand, that their rig uses the same
transistors in its RF PA. Distortion started at less than 110 watts.
•
Increased heat dissipation may be a problem. Nobody has any design/spec data to tell
how severe a thermal gradient the heatsink and fan was designed for. Even if the PA
transistors could handle the heat, other components might not.
•
Increased power supply current could cause unexpected problems. What happens to your
external power supply when you demand 30+ A on transmit? What about the 746's
internal voltage regulators?
•
Increasing the power by 50% more than doubles the RF voltages within the internal
ATU. Thus, making it more prone to arcing and burnout.
•
Differing part tolerances can surprise you. It's much easier to compensate for component
variations when you stay well within their tolerances. Thus some rigs may be more prone
to the above problems than others. Just because one ham's rig worked is no guarantee
that your's will.
On the plus side, you might be able to increase your RF output by as much as 1-2 dB.
That's a lot of potential problems for a meager gain. Most hams don't feel that it is worth it.
If you really need more than 100w out, then you should probably consider an amplifier.
7.4
I'm brave; what untested "mods" are there?
While several other "mods" have been discussed, to date, we don't know of anyone brave
enough to try them.
Replacing PIN Diodes in the Demodulator
Likewise, it is speculated that the IC-746 has cheapo PIN diodes in the detector circuit.
Again, in theory, replacing these with higher quality components (closely matched) would
improve performance, in particular, the 3rd order intercept point. This mod even helps the
famous IC-781, which is where the idea came from.
The IC-746-PRO is not eligible for this experiment. It uses it's DSP for modulation and
demodulation.
Page 86 of 113
2003-02-08
