| Icom IC-751 (IC 751 IC751) Allow CW Xmit & USB recieve split mode
Allow CW Xmit & USB recieve split mode to still use the CW VOX. This allows
one to operate with limited privaledges when communicating with SSB stations
above 10MHz. Below 10MHz, the CW receiver is actually LSB so split operation
in that case is effortless and does not require the split oepration to be
invoked. The original bogus operation can be confirmed by placing the rig
into CW Tx and USB Rx split operation and operate the key. A more `graphic'
example of this operation is CW Rx and USB Tx split and operate the key
(scary eh? :-).
1 4.7Kohm resistor and 2 1N914/1N4148/1N4448 diodes
SCHEMATIC: +8V (Pin 14 of IC1)
| | | | /
| |1N914 | 1N914 | /
| _|__ _|__ | +--o Split Switch
| / / | ___|___
D11 | __/__ __/__ | / / / / o-----> to `split' display
| /| | | | | | segment driver
|/ |_|_/____|______|______/__|____ |
| | / | | / |
| | > > |
< R29 < R26
>5.6K > 4.7K
On the Main PC board, there is only one cut trace because R29 & R26 are
both fed from 1 trace and isolated from the rest of the circuitry. One of
the diodes is surface mounted on the solder side of the board over the
cut. R29 is unsoldered so that a thin wire (from w/w or pulled from a
ribbon cable) is then subsequently inserted with the R29 lead back into the
hole to bring R29+R26 common point up to the top of the main board.
The 4.7Kohm resistor is soldered to pin 14 of IC1, the other end of the resistor
is soldered to the anode of the other diode's anode and another long wire
to be routed to the split switch. The cathode of the diode is attached to
the wire inserted earlier with R29.
All the components may be surface mounted if desired on the bottom of the main board, but I chose to perform this mod
on the top of the board to allow easier removal of the main board for
servicing. The long wire that was attached to the second diode and the
resistor is routed to the empty pin on the split switch that is driven to
ground when the switch is in the OFF position.
The CW VOX will be active when using split mode, even if neither the
transmit or receive mode are the CW mode.