Removing The Bcb Attenuator; What "External" Mods Are There For The Ic-746; Remote, Direct Frequency Entry Keypad; Cordless Headset Microphone - Icom IC-746 Faq

Removing the BCB Attenuator

A few folks have noticed that the IC-746 is less sensitive below 1.6Mhz. This appears to be
due to an additional attenuator being switched in to protect the first RF amplifier from
overload by comercial broadcast transmitters.
Some theorize that removing the extra attenuator (by simply bypassing it with a jumper)
would improve the sensitivity. This involves R11 - R14 on the RF board (see p 11-5 of the
Service Manual for the schematics).
Others point out that the atmospheric noise level on that band is too high to put any
additional sensitivity to use.
Again, we don't know of anyone willing to admit to performing any of these modifications.
If you perform one of these (or some other esoteric "mod"), then we'd love for you to share
your results with the rest of us.
7.5

What "external" mods are there for the IC-746?

These modifications are not made on the IC-746 internal circuitry, but are external interfaces
of one sort or another.

Remote, Direct Frequency Entry Keypad

W2FS wrote an article for the Dec 99 QST entitled "A Direct Frequency Entry Keypad for
ICOM Transceivers". The "Millennium QSYer" is based upon that design and available
from:
http://www.john.hansen.net/keypad.htm

Cordless Headset Microphone

Some hams have come up with a clever way to add a cordless headset to their rig. Basically,
you find a cordless phone with a soundcard interface on it; something designed to work with
your PC as an Internet phone. (The IBM3330 900Mhz phone is a popular choice) You hook
up the phone to the transceiver like you would a PC, and then use VOX to control TX/RX.
Some have had great success. W8WWV provides all the details at:
http://www.seed-solutions.com/gregordy/Amateur
Radio/Experimentation/CLessPhone.htm
Instead of a cordless phone, you could try using one of the cordless microphone headsets
they sell for use with computers.

Automatic Antenna/Amplifier Selection by Band

These are also refered to as "automatic band decoders". Its the art of contolling external
equipment (amplifiers, antenna switches, etc...) based upon what RF band the transceiver is
currently switched to. There are two basic approaches for this. One approach attempts to
interpret the data transmitted by the CI-V interface, Icom's amplifiers are a good example.
Others attempt to decode the band voltage available from the ACC port. Most "projects" use
that approach.
IC-746 FAQ
Page 87 of 113
2003-02-08